DEC, OF Y 1909 WASHINGTON, PUBLISHED BY THE CARNEGIE INSTITUTION OF WASHINGTON B VOLNEY M. SPALDING DISTRIBUTION AND MOVEMENTS DESERT PLANTS CARNEGIE INSTITUTION OF WASHINGTON PUBLICATION No. 113 PRESS OF GIBSON BROS. WASHINGTON, D. C. CONTENTS. Page OTE COIES, «Gt 0 SN cc rr A eae ee eee I~4 DEEP eASOOCIATIONS AND HABITATS, .-...'..-.03 0-4 o0sees0ss0 03s we 5-2 (1) The river and irrigating ditches; association of hygrophytes........ : (2) The river banks; association of cottonwoods and willows........... 8 (3) The flood-plain; mesquite forest association...................0.. 9 (4) Salt spots; association of salt-bushes...................... ae 13 (5) The wash; palo verde-catclaw association. ...............000.005. 14 (lee eMNeSisIKG SlOPeS 25.5...) 2 ans +s euers Ee Oe Ee ee. 16 (Ce reocote- bush associa tion, £5.08 ot a. oe ee ee 16 (Gye raticeria association sagcctek « tlre edge pees eee, eee gee 17 Mie LGN A sah cas. ial, tease, ot icant its eit pee. EET. tick Pam? eae SE ae 18 (a) Association of Fouguieria and Parkinsonia microphylla....... 18 (b) Association of Cereus giganteus and Encelia farinosa......... 18 KC wi Opi ASSOCIA i@tbin chute r Sale a ee ant ene ti ee 19 (GeV PUN IONANG ASSOCIATION wate ch tee atte his lease 19 (5) ‘Superficial soil dayerss association of annuals 5 «21040 0 a ass 20 (a)\eonade-loving cpectessiy. oo. nik. Aiea. Sieg ees A Bas, Beet ad 20 COL Isnt lovin ne sertes ey a A det ka iy ne ce eee es 21 (Oe aia ctlic ati svt DINE PEAILS snes 9. ora dubctite «pd cot eite Aes ae 22 Pichens or the Desert :Labottory domatt, 046 wwe hie ass dabeyan 24 Oe Miscella nents initoduced SNCCIES., 7 cos couse eke ee as uNdee 27 LIMA COCAL MI MSTRIBUTIONIONROPRCINST, Anmiew a¥ ea ds 5 SHEE. fh od. es 29-66 Hops piic na isoll relations, fe 2 ee eos dee. Pel 29 ORCL UPENOSU LED, Set PREP tyr ee ates ee A OE RE, 29 aE TALE HLG Ma ee Be ae dinss AM Che thin 38 tei Aaa Bea dyin @ 3PM t 30 FEU POCA TILTED IMac xi hon Re Mes OMe yh te Rew teen 8 2 eo ed Gate 31 PCL OTIC PAIN rhe es... AE a Oe meee sc ee EP Ba EA OLD TO DOU Aine x OM Bat Sie eee Nant aera aie Suny’ Sylpeive ep ayers hs 36 COMPARA Ca SUUCIOS Terai s PIT oe wise jetn ou, eine Dee wales baa Te a NEedS a idles PENCIES Ol GISDEL S31. We aes 2) ee Peg el. Ge OI es 47 Tea 10 ie COM Perition aN SUCCESSION: fy occ pee. oe bao sin osha 2 51 Habussnd stticturesirelatedto, distribution. f.-0: 6.03 Bi a Ly a he. root-systemol Cereus c1vanteus, 6443 6 ese fda ed ae vss 59 TAD ENVIRONMENTAL AND? HISTORICAL, FACTORS)... 0. foe ee eee cee ene 67-102 The geology of the vicinity of the Tumamoe Hills............5......... 67 eta (abl yam en et eh te a dda ped y atek.k 73 Cy er eR tt ee ree tN aN No Sines wip. ee v2 Sy she 74 tee i ern re ee oie a oan ss Sie Sip TE Ge aye 79 Piletemlstomtesescrt | abOratory COmainy vec 8 bak feel ns ne es be ess 83 ETE OS COW ATA EN TRTTES fo) oe Boe PM lt a Oe As iad a a a 94 (ISSR ES ONSEN lho © Dec Renata ia aie! ok! a nr 94 Pemipers etre tecorde ea ianen ee cu avs et 5 Fhe steko avoss 96 DiCastitemenia OmevanGla MOU RE Raa Pee re eo kk Saw elk 99 PITIAES Ol 1 ett Ota OLY COLA ie ees in Se ee a 101 IV. VEGETATION GROUPS OF THE DESERT LABORATORY DOMAIN.......... 103-112 Ve. LH ORIGINGORS DESERT CHLORAS ace aia al tts Aes kee hep aes 2 113-119 Rote uy Wd NIE LITSCUSSION tac 4 ee ene, In nae 9.2 8d wiring lee I 21-137 ‘Lhe plantassociat ions, 24r Greree eam fulton 1. telat es Wa SS. 121 Heaphiorelationsy. 2005.21, 22S Pee CAO IG Are aC sy. B22 Concurrent action! different factors oq. 0 es cee as, Phen | 127 OCA UMD Y CINETILS oo ha eine ae Single individual of Cercidium torreyanum. Branching opuntias in background. a i a pete SO BR Or 0, * ee We , Tame eS ytd AO eekis Ephedra trifurca in wash west of Desert Laboratory. CAMPBELL ART CO., ELIZABETH, N. J. PLANT ASSOCIATIONS AND HABITATS. 15 of Tumamoc Hill. The catclaw deports itself in the same way. Ephedra trifurca (plate 6), another characteristic species, ranges still more widely, approaching the habits of the creosote-bush in attaining its best develop- ment where there is an abundant water-supply, but, like the latter, capable of maintaining itself successfully where the water content of the soil is lower, especially on light, more or less sandy soils. A few other woody species find in this habitat a congenial home. Con- dalia spathulata attains here its best development. Condalia lyciordes, a companion of the mesquite, advances with it up the washes, and Celtis pallida, here a plant of the cliffs, also occurs in the wash, absolutely avoiding the intervening slopes, thus presenting further evidence, if such were needed, that soil-water is a factor of prime importance in deter- mining the distribution of this association of plants. Five of the species that have been named as members of this association _ have been observed by Blumer (1908) to change their topographic loca- tion with altitude. These are Cercidiwm torreyanum, Acacia greggit, Prosopis velutina, Condalia lycioides, and Celtis pallida. At Tucson, at an altitude of 2,200 to 3,000 feet, all of these inhabit the washes, and with a single exception (Celtzs pallida) are hardly met with at all else- where; but at higher elevations, 3,500 to 4,500 feet, in the neighboring mountains of the Tucson Range, the Santa Catalinas, and the Rincons, they are found spreading out on gravelly and other upland soils, no longer confined to washes, and deporting themselves as ordinary members of the shrubby upland growth there prevalent. Taking these higher eleva- tions as the point of departure, it is found that even 1,000 feet lower all these species exhibit a marked tendency to confine themselves to water- courses or, at all events, to places where there are good conditions as regards soil-moisture and some degree of protection from the more extreme desert conditions prevailing at the lower levels. The single individual of Yucca elata, a plant of higher levels, that has been found on the Lab- oratory domain, is at the edge of the wash, protected by the higher vegetation around it. It should again be noted, as already suggested, that many of the char- acteristic species of the habitats thus far discussed, though exhibiting more or less plainly certain structural features distinctive of xerophytes, are semi-mesophytic or mesophytic, in some cases even hydrophytic, as regards soil relations. The willows and cottonwoods of the river-banks are, in their habits, what they are the world over. The mesquite of the flood-plain sends its roots down to the water-table, and elsewhere is restricted in its range to habitats in which a satisfactory water-supply is at hand, and the palo verde and catclaw of the washes evidently have much the same dependence on a sufficient amount of soil-water. The same thing appears to be true of various species of salt-bushes, which follow watercourses, or—in the salt-spots—occupy places of seep- 16 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. age. In view of their habits, it may fairly be questioned whether such xerophytic structures as some of the salt-bushes exhibit stand primarily in relation to “physiologically xerophytic”’ soil conditions or not; in fact, it seems not at all improbable that they may be found to fall into the same category with the mesquite and catclaw, exhibiting certain xerophytic structures which are useful in the dry air of the desert, and which also in cases of extraordinary drought successfully regulate tran- spiration and make less draft on the resources of the plant. (6) THE MESA-LIKE SLOPES. (a) CREOSOTE-BUSH ASSOCIATION. The long, gentle slop2 of the “mesa,” as it is commonly but incorrectly called, rises from the flood-plain, at first with an almost imperceptible grade, becoming steeper as the ascent continues to the hill above. Its soil, as already stated, is mainly gravelly or sandy, with but little loam and with a considerable amount of caliche. ‘The slope and the nature of the soil insure perfect drainage and aeration. But with the poor soil, with relatively little capacity for the retention of water, it is plain that we have passed, almost at a step, from soil conditions that may be classed as mesophytic, or semi-mesophytic, to those that are suited only to dis- tinctively xerophytic plants, such as grow where peculiarly trying con- ditions prevail. Under these conditions, as might have been anticipated, nearly all of the perennial species of the flood-plain abruptly cease; in fact, the creosote-bush is the single one that. is capable of successfully holding the ground on the worst places, and even this is dwarfed in the struggle to maintain existence where the water-supply is never abundant for any length of time, and through a large part of the year is necessarily meager in the extreme. Yet, in spite of these untoward conditions, the Larrea claims this zone as its own, and has produced upon it an almost pure growth of a single species (plate 8). It is impossible, as yet, to enumerate completely the peculiarities of this plant, structural and physiological, which have enabled it, more successfully than any other, to cope with the worst of desert conditions as they exist in the Southwest. Some of these, however, are obvious. It is provided with a root-system (plate 7) which both penetrates deeply and also branches widely near the surface, thus being in a position to avail itself of water that accumulates at either level; it is capable, as few other species are, of absorbing appreciable quantities of water through its leaves, and these are admirably protected by varnish and in other ways against excessive transpiration. With the coming on of drought a large percentage of its leaves are thrown off and a still further reduction of surface is accomplished by the leaves becoming checked in their devel- opment long before they have attained their full size, as seen in individ- SPALDING PLATE, 7 : Creosote-bush a year old, showing comparative extent of top and root-system. Vegetation of the wash. In foreground Yucca elata. “© CAMPBELL ART CO,, ELIZABETH, N. J. SPALDING PLATE 8 ty Zone of creosote-bush at the foot of Tumamoc Hill on the north. In the background Santa Catalina Mountains beyond the flood-plain of the Santa Cruz River. tf Tucson slope beyond the wash west of Desert Laboratory. Franseria deltoidea and Opuntia fy fulgida constitute the characteristic vegetation at this point. CAMPBELL ART CO., ELIZABETH, N. J. i THE Lippapy OF ine ea ARIVERSHTY gp Ebuors ae PLANT ASSOCIATIONS AND HABITATS. YW uals of the slopes compared with those of the flood-plain and washes. Its mode of branching and of reproduction from the root is also advan- tageous. Whole systems of branches die, and thus permit their share of water from the soil to go to others, and if, under extraordinary stress, the whole top perishes, fresh shoots from the root come up upon the return of rain, and vigorous growth again takes place. Fitted in so many ways, and probably in others less obvious, to cope with the vicis- situdes of its habitat, the Larrea holds complete sway in this zone, and from Texas to California the broad belt of creosote-bush, covering’ the long slopes that form the approach to the mountains at different altitudes, presents a most striking and characteristic feature of the landscape. A few other species are of occasional occurrence in this special habitat of Larrea. ‘Thus on the slope at the foot of Tumamoc Hill a very few individuals of Fouquierra splendens are established, and in places Opuntia julgida is frequent; none of these, however, approach the creosote-bush as the universal and distinctively characteristic species of this zone. As the slope advances upward with the long continuance of disinte- gration and erosion, the creosote-bush advances with it, and the presence of this plant, both as the successful pioneer and the final possessor of the soil, may be seen almost everywhere throughout its range. Thus we have the interesting case of a well-marked habitat, with a single spe- cies forming in it, at least in places, a perpetually renewed close asso- ciation of its own. The description just given applies to the slope as seen near the foot of Tumamoc Hill and in situations such as the “alluvial fans,’’ where - the conditions of slope and soil characters are essentially similar. There are wide areas commonly included under the term “mesa”? upon which a greater variety of conditions, with corresponding differences of vegetation, prevails. An example of this is the ground included in the Laboratory domain lying to the west of the wash, presently to be described. (b) FRANSERIA ASSOCIATION. Beyond the wash, on the Tucson slope to the west of the laboratory, and elsewhere on the domain, areas of considerable extent occur where there is a soil of coarse texture, approaching gravel, on which /’ranseria deltoidea and Opuntia fulgida constitute the greater part of the vegeta- tion. ‘he former is often very numerously represented (plate 8), and in many places is not accompanied by the cholla, but where the two attain their best development they are likely to occur together. I*requently Krameria canescens and a few other species are associated with them. As far as appears from present evidence, this association is one that is determined first of all by soil relations. ‘These are described in a later paragraph. 18 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. _ (7) THE HILL. Above the Larrea zone the hill is the habitat of a large number of con- spicuous and characteristic perennials, which, although they may be classed together as a single association, differ among themselves to such an extent in ecological traits and choice of habitat as to call for consid- eration under separate groups. (a) PLANTS OF GENERAL OCCURRENCE ON ALI, EXPOSURES; ASSOCIATION OF FOUQUIERIA AND PARKINSONIA MICROPHYLLA. The species of this group, more than any others, give its character to the vegetation of the hill as a whole. Growing as they do equally well on all exposures, to differences of which members of other groups show remarkable sensitiveness, they form at once the most widely spread and most typical representatives of the vegetation of Tumamoc Hill (plate 9). Their adjustment to a wide range of physical conditions seems well-nigh perfect, yet it is exhibited in widely different ways. The habits of Fouguierva and Parkinsonia, to go no further, are very different, as regards the production and fall of foliage leaves, arrangements for pro- tection, and other ecological characters, but they grow side by side on all exposures and on various soils, so that, however limited some of them are as to geographical range, it is plain that within its limits they have attained a high degree of adaptation to widely varying soil and atmos- pheric conditions, and are to be reckoned as highly successful desert species. (b) PLANTS OCCURRING ON SOUTHERN EXPOSURES AND LARGELY WANT- ING ON NORTHERN ONES; ASSOCIATION OF CEREUS GIGANTEUS AND ENCELIA FARINOSA. The species just named are closely and widely associated and are both far more numerous on southern exposures, as well as eastern and western, than on northern ones. ‘This is strikingly shown on the two sides of the gulch adjacent to the Desert Laboratory on the southwest. On the right side of this gulch, with a southern and partly western aspect, there are upwards of 70 sahuaros and the ground is almost covered with a flour- ishing growth of Encelia, numbering thousands of individuals (plate 9). The left bank, on the other hand, with its generally northern aspect, has less than a dozen sahuaros and only a few scattering groups of Encelia (plate 10). ; Observations of temperature and humidity and experiments with seedlings have been in progress for some time, with a view to determining as far as possible the factors to which this striking limitation as regards local habitat is due. (See p. 44 et seq.) SPALDING PLATE 9 * ‘ Y Slope of Tumamoc Hill, showing a strong growth of characteristic vegetation in which Fouquieria splendens and Parkinsonia microphylla are conspicuous. e s Right side of gulch near Laboratory, with generally south exposure. CAMPBELL ART CO., ELIZABETH, NW. J. PLANT ASSOCIATIONS AND HABITATS. 19 (c) PLANTS OCCURRING ON NORTHERN EXPOSURES, BUT WANTING ON SOUTHERN ONES; LIPPIA ASSOCIATION. On the left side of the gulch just referred to, and near its head, Lippia wrighttt forms an extensive patch (plate 10), and in the vicinity of Tuc- son it frequently occurs on similar northern exposures, never, as far as observed by the writer, on a southern exposure; but in the Chiricahua Mountains and elsewhere, as shown by Blumer (1908), it exhibits a marked variability in choice of aspect as governed by altitude; thus, at elevations of 3,000 feet and under it grows only in protected places of north aspect, but loses its aspect preference at altitudes approaching 5,000 feet, while at those near 6,000 feet it is definitely limited to southern exposures. It appears, then, that this plant completely changes its aspect preference within a range of not more than 3,000 feet. At the lower levels it requires protection from too severe desert conditions, and finds this on sheltered rocks of northern aspect. At the higher altitudes, appar- ently requiring protection from cold, it finds a congenial home on warm southern exposures, while at intermediate elevations, in the neighborhood of 5,000 feet, the extreme conditions of both higher and lower altitudes are so far modified that it grows on all exposures. Various other species show at this place a distinct preference for the northern exposures of the hill. Among. these are Abutilon imcanum, Brodiea capitata, and many others, annuals even more conspicuously than perennials. It is evident, however, from the facts cited in the case of Lippra, that this choice of aspect is not necessarily constant, and that direction of slope determines distribution merely as it presents a combi- nation of conditions which may change so greatly, even within a few miles, as to completely reverse the aspect preference of a given species. (d) PLANTS OF THE CLIFFS; HYPTIS-NICOTIANA ASSOCIATION. One species of each of the genera just named is found growing almost exclusively on the abrupt cliffs of Tumamoc Hill and on similar cliffs elsewhere. Celtis pallida, though by no means confined to the cliffs, is of common occurrence on them, where it evidently finds a congenial home. ‘The factors concerned in determining the choice of habitat exhib- ited by members of this association are not known. It may well be that where there is so little soil the result may in part be the outcome of com- petition, but regarding this point we are without positive knowledge. Hyptis and Nicotrvana are rarely seen growing elsewhere, though the latter is sometimes found growing in the sandy soil of washes, and in this latter habitat Celtis is of rather frequent occurrence. I am disposed to think of water-supply as again the main factor. There are probably pockets or fissures in the rocks where Hyptis and other plants obtain what they need, and the occurrence of Celtzs and Nicotiana in washes looks to this also. 20 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. (8) SUPERFICIAL SOIL LAYERS; ASSOCIATION OF ANNUALS. » Thus far, attention has been directed wholly to perennial species which, rooted in their places and remaining there for a period of years, constitute the more permanent and conspicuous elements of the vegetation. There are, however, a very considerable number of annuals which, at certain seasons of the year, become a highly characteristic and conspicuous constituent, and whose habits and distribution involve interesting and important problems. As in the case of the general association of per- ennial plants of the hill, we are here dealing with a more or less composite biological group, which, however, covers a wider area, and is perhaps even more influenced by distinctively local conditions. This, in its turn, will be studied to best advantage under several groups, which, though not sharply delimited, are sufficiently well defined. Taking the winter annuals first, two divisions based on physiological requirements are recognized. (@) SHADE-LOVING SPECIES. A good representative of this group is Parietaria debilis, which grows luxuriantly in the continuous shade of rocks on northern exposures. The water-content of this plant is very high, the stems having the shining pellucid appearance of the eastern clearweed, and there are no indications of specially developed means for the prevention of excessive transpira- tion. Though designated as shade-loving, because of its almost exclusive occurrence in the deep shade of rocks, there is, nevertheless, evidence ‘that its growth here is conditioned by moisture, rather than lessened light intensity. It ventures here and there a little beyond the shade, and though strikingly modified in form and structure by exposure to full insolation for a part of the day, it is nevertheless capable in this situation of maturing its seeds. It is apparently a plant of essentially the same physiological requirements as the so-called shade-loving species of mesophytic forests, and in the one case as in the other jt may well be questioned whether, in the complex of physical factors necessarily in- volved, light intensity plays as important a réle as has been attributed to it. In any case, it is to be understood that the classification here adopted is retained chiefly for convenience in discussing the observed facts. A number of species of winter annuals grow luxuriantly on northern slopes and in the shade of rocks and bushes that are hardly met with on full southern exposures. Such are Bowlesia lobata and, to a less marked degree, species of Phacelia, Amsinckia (plate 11), and others. study of the habits of these plants, however, indicates, quite as plainly as in the preceding case, that the water relation is of primary importance. Bow- lesta, for example, which has grown thickly in the shade of a creosote- bush or palo verde, continues, when they are destroyed, to produce new crops year after year on the same ground, where the accumulation of humus insures a better water-supply. This and the other plants just SPALDING PLATE 10 Left side of gulch near Laboratory, with generally north exposure. Lippia wrightii forming a nearly pure growth on the left side of the gulch, near its head. CAMPBELL ART CO., ELIZABETH, N. J. THe gipeary OF i#é CNSISAaITY gf ILLnars PLANT ASSOCIATIONS AND HABITATS. a named are entirely capable of successful growth in the full light of the sun, provided the root-system is still in soil that supplies a sufficient amount of water. The light relation, notwithstanding the apparent choice of shade on the part of these species, appears, therefore, to be subordinate to water-supply as a factor determining local distribution. (b) LIGHT-LOVING SPECIES. Many of the winter annuals of Tumamoc Hill grow everywhere in the open, where they are fully exposed to the sun, and to a greater or less extent, also, where there is some shade; such are species of Harpagonella, Pectocarya, Plantago, Daucus, Erodvum, and other genera. ‘These also are far more numerously represented on northern than on southern expo- sures, but from the fact that the range of light intensity under which they habitually accomplish their normal development is so great, there can hardly be any doubt that the local distribution of these species, like that of the preceding sections, is correlated first of all with water-supply; and far less, if indeed to any appreciable degree, with light intensity. In its ultimate analysis, therefore, the local distribution of the winter annuals here represented is fundamentally based on the water relation. So broad a conclusion should receive confirmation from the determination of physiological constants involving a prolonged series of experiments, but the appearance or non-appearance of both these and the summer annuals is so obviously related to rainfall that any other conclusion as to their relation to water-supply is, with present evidence, impossible. The summer annuals appear after the summer rains, during the period of the highest temperature of the year. Once the ground has become wet they germinate and develop with great rapidity, some of them grow- ing to a large size and in such numbers as to form, in many places, a conspicuous feature of the vegetation. They bear the same relation to summer rains that the winter annuals do to winter rains, and their behavior necessitates the same conclusion as to the fundamental impor- tance, in their case as in that of the winter annuals, of the water relation. Not less certain, however, is the fact that the habits of both are directly correlated with differences of temperature. It is impossible, for example, to induce the germination of the seeds of winter annuals in summer tem- peratures, unless they have previously been subjected to a low temper- ature. Thus while water-supply, with annuals as with perennials, is a chief factor in determining distribution in space, differences of temperature determine with remarkable precision and certainty the distribution in time of the winter and summer annuals, and the face of the landscape is twice a year changed to correspond with their biological habits. It results that areas which are densely covered with winter annuals in February and March afford ample room and all the necessary conditions of development to the luxuriantly growing summer annuals of August and September. 22 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. (9) PARASITIC AND SYMBIOTIC PLANTS. Though not forming associations properly comparable with the fore- going ones, the parasitic plants of the Laboratory domain call for notice. Two species of mistletoe are widely distributed in this region, one of which (Phoradendron californicum) is of fairly frequent occurrence on Tumamoc Hill and the adjacent valleys, where it grows on Prosopis velutina, Parkinsonia microphylla, Cercidium torreyanum, Acacia con- stricta and A. greggu (plate 11). Of these P. microphylla and the mesquite are its most frequent hosts on the domain, where it has been observed but once on A. constricta, and once on Cercidium torreyanum. The other species, Phoradendron flavescens, has not been found within our limits, but it is of common occurrence in the valley of the Santa Cruz River in the vicinity of Tucson, growing on cottonwood and ash trees. In contrast with the limited number of hosts which are here affected by these species of mistletoe, Mr. J. C. Blumer states that in the Chiri- cahua Mountains, at altitudes of 5,000 to 6,000 feet, he has observed Phoradendron flavescens growing on two species of ash, on sycamore, on two species of cottonwood, and on two of willow, and in its form pubescens on many oaks. This is as might be expected from the far greater variety of hosts and the greater range of environmental con- ditions in the mountain region. Important observations and experiments have been made on both species by Cannon (1904), to which bare reference can here be made. These relate to germination and mode of penetration of the host and to the rate of transpiration of the parasite as compared with that of the host. In regard to the latter it was found that in the various experi- ments undertaken the parasite transpired more rapidly than the host, from which there results an unnatural draft on the resources of the host, which is often followed by the death of the infested branches, the con- sequent great disfigurement of the tree, and, in some cases, its ultimate destruction. It does not seem, however, that any of the hosts affected have been appreciably limited in their distribution by the action of these parasites. As for the distribution of the parasites themselves, it appears from the observation of the author referred to that it takes place from tree to tree by the agency of birds, but its distribution in a tree is such as to indicate that when once the higher branches have been infected, in due time seeds from this source reach the branches below without the agency of birds. An exceedingly interesting case of parasitism, in which a large number of hosts is involved, is that of Orthocarpus purpurascens palmeri, which in springtime grows so thickly on the sides of Tumamoc Hill as to give them a reddish tint noticeable at considerable distances. Dr. Cannon has identified some 20 species of plants on the roots of which this parasite fastens. SPALDING PLATE 11 Fe - ‘ed Rank growth of winter annuals, at this place chiefly Amsinckia spectabilis. CAMPBELL ART CO., ELIZABETH, N. J Me 4; + > ° mn 4 : a s j Ae coe c i] = a i 7 ae 7 * .% ie. es 7 arte tits vce > —— ‘ ® ee | | THE LIBRARY | >) SEA, | uiyenstty GF UNOS thats PLANT ASSOCIATIONS AND HABITATS. 26 As far as present observations extend, the fungus flora of the Labora- tory domain may be characterized as insignificant. A few parasitic forms of the Perisporiacee and other groups occur from year to year on certain annuals, and a few saprophytes have been found on bark, and, in two or three instances, growing in the low ground of the wash. Undoubtedly careful search would result in the collection of a considerable number of species, but the fact remains that the fungus flora here is extremely limited, as it would seem it must be from the severe conditions imposed. This meager showing is again in strong contrast with the rather rich display of fungi reported by Blumer (1908) in the Chiricahuas, and prob- ably matched in other neighboring mountain regions where favorable conditions prevail. | Better developed, and of more ecological interest, are the symbiotic plants constituting the lichen flora, an account of which is given on pages 2AOs2 7. 24 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. _ LICHENS OF THE DESERT LABORATORY DOMAIN.! The lichens of the Laboratory domain form a remarkable assemblage of plants. Irom collections made by J. C. Blumer and V. M. Spalding, 32 species have thus far been identified, but many more species are certain to be found when the ground is more exhaustively worked. ‘The collectors were asked to find any loosely foliose or fruticose lichens, and only a single loosely foliose species was sent and not a single fruticose one; the former, moreover, was possessed of very special adaptations. But very few were collected from the soil, although they were frequently looked for, and repeated requests for material from woody plants brought nothing but a few sterile and poorly developed specimens of a Physcia and a Placodium. These were collected on Parkinsonia microphylla very close to the ground, among rocks on a north slope. Of the 32 species 24 were found on rocks and, as shown by Fink (1899, 1904), bear a striking general resemblance to those occurring in regions of greater rainfall on exposed granite and southward facing riprap, which represent xerophytic habitats. One may look through the whole list of 24 lichens growing on the rocks of Tumamoc Hill without finding more than 4 species with conspicuously lobed thalli. These are Placodium elegans, P. murorum, Lecanora murals, and Parmelia conspersa; and these when compared with lichens of the same species from more moist climates show, as a whole, a perceptible shortening of the lobes of the thalli. This condition of affairs may stand in relation to the dry air of the desert, or possibly to the high winds which prevail there. It is well known that the more a thallus is branched or lobed, the more young, tender, growing points are exposed, and the greater the amount of transpiration of moisture. It is also true that many fruticose lichens, certain Evernias, for example, notably lacking on Tumamoc Hill, can scarcely maintain themselves in open places, where they are subjected to strong gales, but seek protected habitats, where they will not be torn from their substrata. These forms, moreover, are usually conspicuously branched and present much surface and many tender, growing areas to the drying effects of wind and a dry atmosphere. The general form, therefore, of the rock-inhabiting lichens of the Labora- tory domain is advantageous from either of these points of view. In general, the 24 lichens collected on the rocks of Tumamoc Hill are protected by some sort of mechanical device, usually a definite pseudo- parenchymatous cortex, and inclosed, dead algal cells, which protect the living algal cells and the fungal hyphe of the medullary layer against the drying effects of high winds and the direct rays of sunlight. Zukal (1895) has observed that the cortex is thicker in certain lichens growing in places where they are exposed more than usual to intense light and dry atmosphere than in the same species in less-exposed positions. One of the most helpful studies in connection with the present problem would be the comparison of some of the lichens of Tumamoc Hill with repre- sentatives of the same species from regions having average conditions of light, moisture, temperature, and wind, with reference to develop- ment of cortex. _ There should also be a more thorough study of the presence and func- tions of coloring-matter in the cortex than has vet been made. Of the * Abstract from paper prepared by request and contributed by Bruce Fink, Ph. D., Professor of Botany in Miami University. PLANT ASSOCIATIONS AND HABITATS. 25 rock-inhabiting lichens of Tumamoc Hill every species having a light- colored thallus shows a more or less evident development of black lines or spots on the upper surface. These lines or spots are so numerous on older portions of some of the thalli as to darken, more or less, the otherwise light-colored surface. Zukal, in his discussion of the protec- tive significance of colors in lichens, speaks of such lines of black as occur- ring on younger or injured portions of thalli to protect the algal cells from the intense rays of the sun in hot regions; but the writer has found the lines and spots better developed over older parts and could not detect their unusual development in connection with cracks of the thalli. In the unsettled state of our knowledge regarding protective coloration, it is very desirable that careful observation should be made of the relation of development of the black areas to the position of the particular plant on the rocks with reference to the sun’s rays. The study of the relation of development of coloration at the tips of the branchlets of Parmelia conspersa to the orientation of these branchlets to the sun’s rays would be specially instructive. The 15 genera thus far collected have been subjected to careful exam- ination with reference to the structure of the thallus and its relation to xerophytic conditions. The Acarosporas, which form a large proportion of the rock-inhabiting species, are cellular throughout, so that the algal cells are unusually well protected against too intense light or too much transpiration of moisture, or both. The same is true of the Endocarpis- cums. The Lecanoras have either an upper cellular cortex or a pseudo- cortex of entangled hyphz, and the Placodiums show similar structure. The one Parmelia is a very closely adnate species, which is found to possess a stronger cortex than the closely related Parmelia caperata, which usually grows in less xerophytic conditions. The Dermatocarpons are all well protected by strong cortices, and Dermatocarpon miniatum, the only species not closely adnate, is attached to the rocks by a very strong umbilicus, while the lower cortex is so strongly developed that no ordi- nary wind can tear the plants from the rocks. Not to enumerate the remaining genera, most of which can not be ranked as important floral elements, the general statement. may be made that structurally the lichens of the Laboratory domain are well protected both against the danger of excessive transpiration and that of being torn away by high winds. The lichens sent for study were collected from 7 stations. They are most numerous on the north side of the dark-colored basaltic rocks which compose so large a part of Tumamoc Hill, and are very poorly represented on southern exposures and on the tuff which has been quarried in a few places for building purposes. At station III, which is a very steep slope on the south side of Tumamoc Hill, facing directly south, at an altitude of 2,700 feet, the lichen habitat consists of loose blocks of tuff and basalt, where nothing in the way of seed plants exists but a few creosote-bushes. Only 7 species of lichens were collected here, 5 of which belong to the genus Acarospora. The frequent occurrence of members of this genus on southward-facing riprap and their very rare occurrence on the northward- facing riprap a few feet away has been noted elsewhere by Fink (1904, p. 278) and, with the data obtained at station III, establish beyond doubt that the Acarosporas, with their strong, protective cortices and their cellular structure throughout, are the most characteristic xerophytes of all our American lichens hitherto studied from the ecological point of view. Tuff is a drier rock than basalt, not holding water so well, and, 26 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. - corresponding to this drier substratum, not only at station III but at other points, the Acarosporas are well represented upon it. Of atmospheric conditions likely to influence the distribution of lichens, relative humidity and air movements are undoubtedly the most important factors. The relative humidity is known to be as low as 8 per cent of saturation at the Desert Laboratory at times of special dryness in summer, and it varies from this to a high percentage during the rainy seasons. The drying winds from the east, south, and west, day after day, doubtless interfere to some extent with the development of lichens on these three sides of rock exposures, accentuating the effect of direct sunlight, thus leaving the northward-facing ledges by far the best habitats. It has been shown by Spalding (1906) that certain desert seed-plants absorb more or less water through their leaves and young shoots, some of them as much as 1g per cent of their weight, and he has also found that some species absorb a very small amount of water-vapor from a nearly saturated atmosphere, through their leaves and twigs. It is thought that this absorption of water and water-vapor through subaerial parts may be of some slight advantage. Jumelle (1892) has experimented with lichens in somewhat similar fashion. His experiments show that lichens, compared with seed-plants, contain very little water at any time, but that the former are much more able to absorb water or water-vapor in the proportions needed than are the latter, according to the results obtained by Spalding. Aside from the gelatinous species, lichens need but little water and are able to obtain all that is required through the general surface, instead | of through specialized organs, as roots. It may be assumed from these investigations, until otherwise proven, that lichens are able to absorb at least a large proportion of the moisture needed directly from water- vapor of the atmosphere and from water falling upon them in the form of rain. As far as appears, however, the statements of Jumelle do not rest upon experiments made on any desert lichens, and similar investiga- tions of some of the lichens about the Desert Laboratory would be cer- tain to yield instructive results. Experiments such as those made by the authors referred to, performed upon the crustose lichens of the desert in the driest condition in nature and giving the relation between fresh and dry weight, would give data regarding the amount of moisture retained in lichen thalli during the driest times. Accompanying this should go observations regarding the length of time that these lichens may be kept dry and then resume active respiration and assimilation on the return of favorable conditions. Since lichens have no special storage organs, nor organs of absorption extending any considerable distance into the substratum, the retreat of the evap- orating surface into the soil leaves any lichens growing upon exposed soil entirely in an air-dry environment, and under such conditions the ability to absorb water-vapor from the atmosphere and to quickly take up water when there are light rains would be a distinct advantage. It is still a question to what extent the rock-inhabiting lichens of the desert may be able to obtain moisture from the rocks on which they grow. The basalt is, in general, more dense and less porous than the tuff, and it seems likely that the latter may give off moisture so rapidly as to be- come too dry to support lichens very successfully through periods of prolonged drought. The less porous basalt doubtless gives off water- vapor very slowly, and this would be more favorable to the growth of SPALDING PLATE 12 Lichens on north face of rocks above Desert Laboratory. eee | THe wBRARY, oie hte WNIVERSSTY OF HLLINGIS os > eo 4 Csuph ir . Tab PLANT ASSOCIATIONS AND HABITATS. aT lichens, especially on northward-facing exposures, where the effect of prolonged drought is least felt, and where, as a matter of fact, a very large percentage of the lichens occurring on Tumamoc Hill are found. The great number of lichens that almost cover the surface of small detached rocks on north slopes near the Laboratory seem to point to the atmos- phere rather than to the substratum as the source of water-supply, but the problem is worthy of much more thorough study than it has yet received. (10) CULTIVATED GROUNDS, WASTE PLACES, AND ROADSIDES; MISCELLANEOUS INTRODUCED SPECIES. Within the limits of Tumamoc Hill and the adjacent flood-plain the introduction of weeds and of various cultivated species has gone on until these have become, in many places, a conspicuous and more or less impor- tant element of the vegetation. The high mallow (Malva parviflora) and cocklebur (Xanthium canadense), for example, have greatly modified the aspect of roadsides and edges of fields. Along the arroyos Arundinaria, and near the old mill quince-bushes and Sapindus, are permanent re- minders of the planting of earlier days. Among later arrivals are the alfilaria (Erodium cicutarvum) and foxtail (Hordeum murinum), both of which have made themselves at home, and their presence is materially felt over wide areas. The physiological requirements of these and numerous other species introduced here, as well as their distribution in relation to local condi- tions, are, to all appearances, much the same as in the different regions from which they came, but it is noteworthy that they exhibit comparative indifference to intense insolation, much like indigenous species already referred to that commonly grow in shady places. With the one group as with the other, a sufficient supply of soil-water is evidently the first essential, and, with this assured, they flourish in the fierce glare of the sun in an atmosphere often of very low relative humidity. é { i, Pn arr Sania s im” yas Oma Reps GE ae mt - e ’ 1(, we ang Wag Pil Preeti.» pahe& t , F y ue Ae: : S « > 7 ro : Na % « ' , ’ f - ‘ nde Thy - © : Ne pas a 2 E 7 Lae ts id > i ry ye =. es ‘ hd ’ ' ' dine Pills i I ' ‘ e = 7 a = , te | dab ites : _o we 4 i ai : » y : : ' t ' U fi ’ in 5 : 7 we ~ a re) é f - * - Og OE ak 7 » 7 7 ’ : - | | : : wd hue: bn poh ann ee BE - . 4 7 > . ut ie aa 7 o a : ; : H ow iu Oh 7 - ? ty ‘ ‘ , i _ ~ wy : Lore i > +h CHAPTER Il. LOCAL DISTRIBUTION OF SPECIES. TOPOGRAPHIC AND SOIL RELATIONS. In the first division of this paper the aim was to present a clear account of the natural associations of plants on and near the Laboratory domain, and to point out, wherever possible, certain obvious relations between local distribution and environmental factors. In this division, dealing more in detail with constituent species of the associations, the attempt to trace cause and effect is carried a step farther. Certain species have been carefully mapped and their habits have been more thoroughly studied with reference to differences of soil and aspect. The species selected for special study are characteristic in their respective places, and the maps show at a glance their remarkable definiteness of habitat preference. The mapping has been done by Mr. J. C. Blumer, and the account which follows is based on his field-notes, which have been placed at my disposal. Observations of soil and air temperatures on opposite sides of the gulch near the Laboratory, made by myself for a number of months, aid in analyzing the complex factors determined by aspect, or direction of slope. The discussion of soil conditions by Dr. Livingston brings to light impor- tant relations and is presented in a later section as a special contribution. Beginning with the species that have been mapped, a certain amount of detail which is indispensable will be presented. ENCELIA FARINOSA. On the Laboratory domain, and in its vicinity, the lower limit of this plant coincides closely with the 2,500-foot contour, but its local distri- bution is evidently determined by other factors than altitude. It is usually limited to steep slopes, and its lower limit is often sharply marked by a few degrees difference in gradient. But steep slopes are here char- acterized by a thin layer of residual adobe soil of high retentive power -for water, and such slopes, with thin layers of soil, point to rock-masses near the surface, either in the form of fissured or laminated bed-rock, or of detached bowlders, conditions which indicate the presence of a relatively high degree of moisture. On this point see Livingston (1906). Thus, the rain of January 2-3, 1908 (0.62 in.), penetrated down about 5 inches at the Laboratory, but only 3 inches at the farm near by. This indicates greater penetrability of rocky soil of this character. This species also shows in its distribution a marked and definite rela- tion to aspect. Other things being equal, its density increases directly 29 30 DISTRIBUTION AND MOVEMEN’S OF DESERT PLANTS. as the aspect becomes more southerly. But south aspect involves greater heat, and here, too, a steep slope also results in greater heat, at least during parts of the year, because of the more nearly perpendicular inci- dence of the sun’s rays. The accompanying map (plate 13) shows the almost entire absence of Encelia from north slopes and from the gentle slopes below the 2,500-foot contour. It appears, then, that FEncelia farinosa is limited to areas having a relatively high degree of heat and moisture. It grows more densely than any other large plant of the Laboratory domain, and is well limited to its own particular habitat. Within this habitat it is limited (a) by sheer cliffs; (6) by such an increase of rocks as to amount to bare talus; (c) by certain areas of creosote-bush, which may possibly prove signifi- cant as denoting an unusually great distance between surface and water. LARREA TRIDENTATA. The creosote-bush is the most abundant, and with the exception of Parkinsoma microphylla, and possibly Acacia constricta, the most widely and continuously distributed ligneous plant of the Laboratory domain. At the same time it is no less limited than Encelia, as regards its best habitat, by certain physiographic features. It occupies, either exclu- sively or as the major element, the gentle lower slope between the moun- tains and the flood-plain. Its upper limit, as a major element, is often very definitely marked by the same few degrees of difference in gradient as the lower one of Encelia, hence the two come together on the contour in such places (com- pare plates 13 and 14). Its lower limit, along the valley, is marked with absolute definiteness by the edge of the flood-plain, and accordingly its principal habitat is seen to coincide with the areas of coarse, gravelly, whitish, transported soil, devoid of large fragments of rock, which char- acterize the lower slope as already defined. Outside of its main belt the Larrea comes in strong in certain places of gentle slope and deep soil, places that have evidently been filled up in the past, but at present are wearing down. Some of these places are situated in the heart of the Encelia belt, but Encelia is absent. This confirms what the main belts show, namely, that Encelia and Larrea are of dis- tinctly opposite tendencies in their relation to certain determining factors of distribution. Encelia, as we have seen, follows areas having a relatively high degree of heat and moisture. Larrea, on the other hand, is preemi- nently a plant of well-drained erosion areas. ‘The main Larrea belt between the hills and the flood-plain is constantly wearing down, as is seen, among other things, from the numerous small gullies over this area, and the exposed sahuaro roots on the plains beyond the wash, where there is a strong growth of Larrea, tell the same story; even the bottom of the wash, where Larrea is present in large numbers, is at present wearing alee pes en nite ad vo ome ah etamaaianae Fe neat ne we lege : fhe A Ah tte tet aod AO a — «4° Ls ry h ’ ; i i ; peal ay wvE % . x pe ate mer Se ce se ee el . : m ‘ s ri ? 8 ) . . . , . 7 ; fis? a f oa ’ lp i c 7 . a ay ’ & M { : ; ‘ ath ee, 2 ; ae e Bei He vs bs 3 yy | ae Pe {) bi ; § ‘ie :s } F 5 Tes ia : Bs 4 My PO at } Hee ¥ ~ { 4 “y, i > ‘ ; ; ; Wi a > | 4 7. i : y =r Pt ' ek i he i, | ie b ' ie e = ae tiaadilie +: an ee sects ten «pom, amet tina ; J f P’ g' ’ . 4 v : 7 Ls t } / Pe ate Chat 2 SS Lae i ; vey. ; Ce eitenir 6 ete y! : Bt nv ¥ 23 pe ied a Yuet daly | mr ne — ; we ease ore ~ — ion = at ssibeeninc AOS, ON WORA TAR YARRALICN Raw INTA TRZOIF, WIAA ck: 7 7 ‘ . * P ( 2) eh 8 4 i (>t. Opawieae a 7° * ri ". as . A ‘ . as od Be ' ” . av 7 . : i _ ™~ Ls Lal oie: * ; aor 116th = # f a Average of over to plants ee ag) as Tr 4 mM T : 1 1 Tt \ r y | | TUMAMOC HILLS AND VICINITY | { | | —— \ ‘ TUCSON, ARIZONA | — | 1 | | = \ SCALE: 6000 he \ | | |- | | \ | | \ | | | | | ; set } | : : ‘ \ : ane ia ae) aes = by oe Pee NT 2x Pd \ SS | y= Basgeiarogy’ i) f ay wes e Me = ina y ONG = = y = af | w EB & is (g | . a BA \ Bas i LEGEND ae 7. S me : Ay | Cereus giganteus / \ # t One dot for each plant *% ft => 4° \ 8 gy , nes ae \2 \ / | Upper talus > ‘ as im Po. z. / = NA | | | + ei yA ’ > ~ — | / = E { f ws i fi ‘ 1 Terrac nk J" . | 2 Upper limit ape [. | | | | i \ cae 1 Lower talus : i les i a | | ar al ” [2 S=V7 | 3 Rock outcrop | aN . / ! fit | ac ] | a | _ | Ml. } ee é “ hy | \ 4 | nM | | by | | ¥ | F ™~ / \> : Séntinel Hit / a) ¥ Yee N\ 2 %) } \ Aged! 1 | : J Sis ? a ‘ & f - c | ae Sy abiibermnieen 5 a Sy | | vere | KS | 4 x ha | | m . | | ae f | ~ | hi ih | s | | : sh a a a oS € = 7+ = ste {-—~ es rene - a = - | j | 4 y , Ss — = a F ’ C. Blumer del,, April, 1go8 yo 2 + 2 5 : 6 : 8 9 il i3 14 LOCAL DISTRIBUTION OF SPECIES. 33 (b) Detached lower talus groups, where coarse angular fragments are accumulated by the washing out of the fine material, are found near the foot of the slopes, dotting areas thickly strewn with basalt fragments imbedded in dark, fine, retentive soil. They usually lie in the bottom of depressions or along the lower course of arroyos. ‘This material has been brought down from above in times past. Some of these areas are good reservoirs for the storage of flood-waters. (6) Gully groups border the arroyos or gullies, and a collection of such groups forms a belt of unusual density following a dry watercourse, or a system of washes. Even where such a course is merely a band of sand it often has the power to attract to its sides the only plants of the neigh- borhood. Such arroyos often have the steep rocky banks which this plant affects, and it is quite probable that the roots also profit by the periodic flow. (7) Deltoid groups are probably the most significant of all. The smaller gullies on the slopes are not always continuous, but sometimes lose them- selves on a pile of rock débris deposited by floods. On the south slope, where they occur, their sides give a warm, southerly declivity, and the bowlder-filled soil is thoroughly saturated by every generous flood that comes along, while it receives the full value of even a tiny rill. All these habitats point to a high degree of warmth as essential, coupled with the best moisture conditions obtainable. The sahuaro is absent from the middle portions of talus slopes, and, speaking generally of mature plants, from cliffs, evidently because of lack of soil. It is comparatively scarce on northerly slopes, and present in intermediate numbers on east and west slopes. It is absent, either absolutely or comparatively speaking, from level land and from slopes cemented by caliche. The outline of the sahuaro groups is often determined by the physi- ography. ‘The belts of unusual density following arroyos and gullies are very evident, almost general, and follow the direction of these. Certain well-marked cases occur in depressions, where no water-channel is in evidence, but where the grouping takes the form of a belt running down hill, clearly marking seepage channels, either present or past, according to the general age and grouping of the plants. On the other hand, the long axis of certain other groups lies along the contour. ‘These will be found to grow along the sides of more or less horizontal terraces. A succession of such terrace groups, but, more generally, irregular rock- outcrop groups, may be seen to make a horizontal belt of unusual density, running about certain hillsides, notably Sentinel Hill on the south, clearly traceable to geologic strata of great comparative resistance to erosion. Protruding tuff-beds were found to be as prolific as outcrops of the different kinds of basalt. 34 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. Another class of instances that may perhaps be put with the phenomena of dynamic physiography are presented by the slopes covered with loose, sliding tuff fragments about the three quarries, and notably on the south side of the west end of Sentinel Ridge. Only Larrea is able to maintain a more or less successful foothold, and even this occurs in distinct rows or beds running up and down hill, unable to resist the products of erosion sliding down the paths between. There is present on such slopes plenty of good-sized rock-fragments, as well as soil. ‘The aspect and gradient are the most favorable ones to be found, but the sahuaro in the case of the west end of Sentinel Ridge is almost altogether absent. Apparently the only thing lacking is a sufficiently stable surface, though moisture and other physical conditions may also be changed profoundly by this instability of surface. Associated with the optimum physical habitat for the sahuaro are often found certain recurring organic associations. ‘These are a rather unusual presence of species of Abutilon, Janusia, Lycium, and several others, on warm southerly aspects, in company with sahuaro groups. One of the best indicators of such an optimum habitat is Andropogon contortus. It almost certainly requires a high degree both of warmth and moistute. Hilarva cenchroides has been located on an area on the south side of Tu- mamoc Hill in company with a large group of sahuaros. A rare colony of Prosopis has been found on the same spot with a typical terrace group. Unusually large specimens of Parkinsonia mucrophylla, growing close together, are very commonly found associated with good sahuaro groups, occupying the same soil. Phoradendron californicum, on the whole rather infrequent, may with great certainty be found suspended, often in large thrifty pendents, from well-nourished specimens of Parkinsonia, standing among thrifty columns of the giant cactus. Not infrequently, where these occur at all, young giants may be looked for with success under the protection of both mistletoe and palo verde. The fact is to be emphasized that rocks, of whatever kind, as found on the Laboratory domain, are almost inseparably linked with the pres- ence of the giant cactus. These may carry with them the ultimate factors governing local distribution in the form of certain soil properties more or less constantly associated with the rocks, or the rocks themselves may act as water-conductors and water-reservoirs by means of the air-space enveloping them in dry times. The moisture of spaces between adjoining rocks, especially basaltic, may be heated by their presence, thus giving a temperature favorable for germination, as is suggested by the occurrence of the smallest sahuaros found growing in such places. The absence of the species appears to be caused by rapid erosion and instability of surface in some places, in others a prominent réle may be played by the impervious caliche, while in still others the most favorable conditions of rock and soil can not make up for the absence of a sufficient degree of insolation, or, what is self-evident, for the lack of seed. A) MW iy ae N ae G =e < Seay : “ees — 3 / is ack | sou ries 9 wa Haig i in Naa NS ae ait amy mg HO < ; : AY “ vi] \\\ A’ NY i a ee @ 5 CO CT atte ‘eur . 8 a uit « MAS NNN Nd ee E : 0 00° nia J HANAN hr aie a J ° we es * F be e s e e | \ \. 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WW ibbge ’ - PHAAY\\NN, ai CZ ey << . ti HNN cae Se UL LIT * LEGEND MAP ad Wash | Bro = 2 oa 22) = a = 8 Q o = = [e) ac Y) OF 7 es ! | | | | | | | | | | la) | fas 2 os 2 = Hh wo j 2 io! i « ee | @ eta Oss = o 9 12) = = fi | ran ah oC € = ce | oa ° 75) (= a es «8 2 o Pe | ae am 0 SB ee = | | ee ey a | a el | Hgts | | @} | eee! | a de Hee! iqeeaet Y Pee a | ah | eee Li | | | | | | | | | | | = = | { = | B= < < ® => Ze = uw @l UES E faa OE eg ° HE = Qa j- N 2 s 3 j (e & = [oh aged 2 | Sd oe 3 “| i ee ee re | wie) ae Mae Coy a a | 5 oe Gee eee | 25 e. eens | Q O = % | O s a a (ve =I | O J. C. Blumer del. Phe Pe A otal awe « - = » a f . ‘ Py a, | Poy Afiuivnaht” Swe Bare ntg Mirko Mayra. ¥ Fags tabi os ae ee } \ ete? © heya y — Se ae ee + & ae + 7s ae wr “ Mea beet - me VS" a a 9aN0 wares: Bvareanmeny mGuEUEU PEK TE Pte ae y ee, ie Am ASHEWN. AE 3 oe . ‘es ; an - f ‘ sr = nes a ca PLATES clumps, very widely Mesquite Woods scattered or rare | No Mesquite small =<- _, Small plants growing singly or in a LEGEND ) ) ST.MARYS HOSPITAL C rae | A. HOEN 4 CO. BALTIMORE CONGRESS ST. JUC.Blumer del e ny BS eet: &, a ee weg? : oF veut - at eof a5 Pas *é 4. 2.5455 aa: : 6 ae wav at g %3 a* Z 3 thee > . ¥ ee a Neca Peres s sa ee sg bis X a3 x my “ oe oe ot, we 8 oF Se 2 bb 6 aR SE oy DESERT LABORATORY DOMAIN AND VICINITY, SHOWING APPROXIMATE DISTRIBUTION OF PROSOPIS VELUTINA OVER AN AREA 3s INCHES PER MILE SCALE OF ABOUT 1,800 ACRES. LOCAL DISTRIBUTION OF SPECIES. 37 of small ridges and troughs, a topography usually typical of Larrea. But such instances serve to direct attention to the fact that underlying the differences of topographical features there must be one or more con- trolling physical factors to which the widely different distribution of these plants is primarily due, and the first of these is apparently the amount and location of soil-water. A large number of observations, too numerous to be given in detail, go to indicate that the presence or absence of caliche has, locally at least, an influence on the distribution of these two species. All about the Laboratory domain the most exclusively Larrea areas are those where caliche comes most nearly to the surface in its characteristic layer, while the mesquite is, as a rule, absent from such areas. Nevertheless a com- parison of the map of Prosopis with that of Larrea (plates 14 and 18) shows that over considerable areas where neither is abundant the two may grow together or in close proximity. All this is consistent, however, with the principle stated above, since differences in amount of available soil-water are certain to result from the presence of the caliche, as it occurs at the base of Tumamoc Hill, and from the disposition of rocks and soil elsewhere. COMPARATIVE STUDIES. It is obvious from the foregoing that soil conditions, even within the narrow limits of the Laboratory domain, exercise a marked influence on the local distribution of plants, and this becomes still more evident when the plants of a wider area, with more pronounced differences of soils, are considered. For the sake of wider comparison in this direction, a study of the vege- tation of a number of areas in Arizona and New Mexico has been under- taken. That part of the Gila Valley lying between Solomonsville and Fort Thomas was visited by the writer in November, 1906. The work there was carried on with particular reference to ascertaining how far the plant habitats of the valley and their most characteristic plant species show a definite correspondence in their distribution with that of the various soils as they have been mapped by Lapham and Neill (1904), of the Bureau of Soils, U. S. Department of Agriculture. As shown by the map referred to (plate 19), a section of the Gila Valley at some place, Pima for example, where the different soils are well represented, crosses successively between the river bed and the lower mountain slopes on either side: (1) The Pecos sand, uniformly present on either side of the river in the valley trough; (2) the Gila fine sandy loam; (3) the Maricopa silt loam, a soil of very fine texture, with some of the peculiarities of adobe; these three constituting the alluvial soils of the district in dis- tinction from the three following, sometimes distinguished as colluvial soils, which are derived from the products of erosion of the mountain sides, PEAT Eso: SOIL MAP OF A PART OF SOLOMONSVILLE SHEET ARIZONA Scale ; 1 2miles Maricopa sandy loam Maricopa sand Maricopa éravelly loam Soils surveyed by ; Macy H Lapham and N.P. Neill Maricopa Riverwash 1903. silt loam LOCAL DISTRIBUTION OF SPECIES. 39 (3) Passing to the Gila fine sandy loam, which comes next to the river sands, it is seen at once that its dense growth of well-developed plants has not suffered, for a long time at any rate, from the effects of periodical floods. The willows and cottonwoods are good-sized trees, 20 to 30 feet in height, the arrow-weed forms dense thickets, and Sueda moquini occurs, in places growing to such a size as to form woody stems some 2 inches in diameter. As here observed, the vegetation of the Gila fine sandy loam may be characterized, first, by the presence of most of the species of the Pecos sand in a much more advanced stage of development; second, by the presence of other plants adapted to its peculiarities of texture and drainage, but incapable of successful resistance to floods; and third, by the absence of various species that affect the heavier soils beyond. (4) The Maricopa silt loam and Maricopa sandy loam, which grade into each other, constitute the distinctive habitat of a dense mesquite forest, which upwards of 30 years ago covered a large part of the valley and was grubbed out by the Mormon settlers. All the best of this land is now divided into productive farms, but enough of the native vegeta- tion remains to make it plain that in earlier years there were, as now, two well-marked associations of plants on this area, which practically corresponds with the flood-plain of the river. These are essentially identical with the two associations of the flood-plain of the Santa Cruz River, already described, namely, the mesquite forest association, con- sisting of a thick growth of mesquite, catclaw, and a few shrubs, with a lower growth of Atriplex canescens and a fairly numerous complement of herbaceous perennials and annuals; and the association of the salt- bushes, here exceedingly well represented and covering large areas, miles in extent, on which at the time of observation Atriplex nuttallu and Sueda moquint were the almost exclusive occupants of the soil. Even these species fail on some of the worst spots marked on the alkali map of Lapham and Neill (J. c., p. 24). On one adjacent to the Fort Thomas Canal there was a good deal of bare ground and much of the Sweda was dying. No more perfect correspondence of soil and association could well be found than exists here, the mesquite forest occupying the flood-plain, with its fine silt or sandy loam and a sufficient supply of water, and the Atriplex and Sueda forming the association of the salt-spots where the percentage of alkali is too high for most other plants. (5) The Maricopa sand, which succeeds the preceding soils as we ap- proach the lower slopes of the mountains, is characteristic in texture and topographical position, and also presents a characteristic vegeta- tion. Here the creosote-bush begins, Yucca elata and certain cacti make their appearance, and Afriplex polycarpa attains its best development. 40 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. Guterrezia euthamie is also frequent. ‘The replacement of Prosopis by Larrea and of Atriplex nuttallit by Atriplex polycarpa, the coming in of cacti and the appearance of Yucca and Gutverrezia, are some of the most distinctive marks of the vegetation of the Maricopa sand as here observed. (6) The Maricopa gravelly loam, forming the slopes and terraces above the Maricopa sand, is distinctively the home of the creosote-bush and a larger number of cacti. With these were found at Pima and near Solo- monsville Kerberlinia spinosa, Yucca elata, Acacia constricta, and some others, and on the flat terraces Fouquierta splendens. The habits of Guherrezia euthanuie, which also occurs here, are the reverse of those of Fouquieria as to local choice of habitat. It is hardly seen except on the slopes, which at Solomonsville were yellow with it for miles, while on reaching the top of the terrace hardly a specimen could be found. Some of the species that have been named are far more restricted as regards limitation to a special habitat than others are. As examples of those more closely restricted in their choice may be named Atriplex polycarpa, which belongs definitely to the Maricopa sand and is scarcely found beyond it, and Atriplex nuttall, which grows altogether upon the Maricopa silt loam, or at most extends into the Maricopa sandy loam. The creosote-bush is limited, almost strictly, to the Maricopa gravelly loam and the Maricopa sand, ocotillo to the Maricopa gravelly loam, and the various species of cacti to this and to the Maricopa sand. The mesquite, on the other hand, although attaining its best develop- ment on the Maricopa loam, ranges from the Gila fine sandy loam to the gravelly loam of the mountain slopes, and Aérzplex canescens has an even wider range, since it occurs also on the Pecos sand. A number of species grow on any soil whatever, from the shifting river-sand to the heaviest silt loam, apparently with almost no limitations, even as regards the amount of alkali in the soil. Arrow-weed (Pluchea sericea) is one of these, and cocklebur and some other introduced species exhibit the same indifference to physical and chemical peculiarities of the soil. The details that have been given point to certain important conclusions: (1) It is evident, in the first place, that there is a remarkable cortre- spondence between topographic features as the result of physiographic processes and the local distribution of plants in the Gila Valley. The tiver-banks, the flood-plain, the long slopes approaching the mountains, and the steeper slopes and terraces above are severally the habitats of different and well-marked associations of plants. Here, as well as in the eastern United States, it may be said that physiography furnishes an efficient basis for an ecological classification of the vegetation. (Com- pare Jennings, 1908.) ? (2) But such studies as have been conducted here make it plain that soil conditions, differing greatly in the different physiographic areas, are the real determining factors governing the local distribution of plants. LOCAL DISTRIBUTION OF SPECIES. 41 The evidence is such that we may unhesitatingly name soil-water content, percentage of alkali, and texture of the soil as three of the more efficient edaphic factors controlling the choice of habitat exhibited by the plants of the Gila Valley. The occurrence of the cottonwoods on the river- banks, of the mesquite on the flood-plain, and the creosote-bush on the lower mountain slopes is certainly conditioned by the first, and the case of the arrow-weed, which grows in any soil whatever where there is water enough, is still more striking. The constant association of Sueda moquini and Atriplex nuttalli1, almost alone over miles of salt-spots, both drained and undrained, is sufficient evidence of the efficient action of the second factor, and the behavior of certain other species points as clearly to a choice based on physical peculiarities of the soil. Thus Aériplex poly- carpa in its close adherence to the Maricopa sand suggests neither water- supply nor percentage of alkali as controlling factors, but more probably a demand on its part for more perfect aeration than is afforded by the heavier soils beyond. (3) The absence from the mountain slopes of the upper Gila Valley of plants so conspicuously present in similar situations on the Laboratory domain as the sahuaro, Encelia farinosa, and Parkinsonia microphylla points to the fact that general climatic conditions are also potent in determining what plants shall and what shall not hold their places here in associations of which they are elsewhere important constituents. From evidence obtained on Tumamoc Hill (p. 47), it appears probable that temperature is the determining factor in the cases referred to. The consideration of this phase of the subject is reserved for another place. (4) But whatever differences of characteristic constituents may appear in the same associations, as they are represented in the valleys of the Santa Cruz and the Gila, the capital fact remains that in the local dis- tribution of their plants these areas are essentially alike. We may add, as subsequent studies of the writer have shown, the Salt River Valley, so that what has been said applies generally to all the great valley systems of southern and southwestern Arizona. Beyond these valleys are the mountains with their mesophytic vegetation. It is in the valleys and on the adjacent slopes that the characteristic desert vegetation attains its best development and exhibits the peculiarities of local distribution that have been described, and since one great valley is fundamentally the counterpart of every other, a thorough study of one becomes the means of interpretation of all the rest. (5) In the Gila Valley, as in that of the Santa Cruz, and in general as far as these observations have extended, everything indicates that causes now in operation have determined the actual distribution of plants in the associations and habitats where they are now found. The general physiographic features remain constant, but boundaries are continually shifting, and coincidently with these changes the plant associations retreat 42 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. slowly from old positions and advance into new ones, as apparently they have done from an indefinite past. If this view is correct, the study of present local distribution and movements is the surest guide to an under- standing of those of earlier times. Observations carried on in more widely separated regions, particularly in the desert near Alamogordo, New Mexico, and along the western limits of the Salton Basin, have confirmed the results that have been indicated as regards the importance of physiographic features and soil characters in determining local distribution of plants. As to the latter factor, how- ever, perhaps no more striking case can be found than that reported by Mr. J. C. Blumer in his recent studies of the ecology of the Fort Bayard (New Mexico) watershed,' in which, within a comparatively limited area, no less than seven distinct societies of plants, each referable to its special rock-formation, are clearly recognized and described. ‘Thus, giving them the name of the rock on which they occur, there are: (1) limestone, (2) quartzite, (3) granite, (4) andesite, (5) rhyolite, (6) conglomerate, and (7) basalt societies. Very remarkable differences of composition are noted in societies close together, or even adjoining. Of two adjacent areas, each including 0.05 acre, meeting on the contour line that marked the contact between basalt and conglomerate, that on the basaltic slope showed 41 individuals of Agave applanata and one of Quercus arizonica, while that on the conglomerate had 36 of Quercus artzonica and none at all of the Agave. Aspect in the same region is recognized as a powerful, and in fact the most powerful factor; and the analysis of the flora, based on this, presents very striking evidence as to its importance as a factor in local distribution. As an example, ‘the east side of Cameron Canyon changes repeatedly from west to northwest aspect, and on the latter not more than 30° in aspect is sufficient to give the entire slope, from top to bottom, over to bull pine.’’ Similar cases have been observed everywhere, but they are particularly well marked in the semi-arid regions of the southwestern United States. An extremely interesting locality in New Mexico was visited by the writer in July, 1906, where at an altitude of 6,000 feet the flora of the pifion association occupies the left bank of a narrow can- yon, while on the right bank, hardly a stone’s throw distant, are the plants of the desert below—mesquite, creosote-bush, ocotillo, Yucca, Agave, and various cacti. On the Laboratory domain, the floristic differences presented by neigh- boring areas, due to differences of aspect, though generally less striking than those just referred to, are sufficiently marked to afford a favorable opportunity for an investigation of the differences of environment to 1Unpublished notes communicated to the writer. LOCAL DISTRIBUTION OF SPECIES. 43 which they owe their origin. For this study the gulch located a few rods southwest of the Laboratory has been selected, because of its convenience of access and because other differences than those resulting from aspect are negligible. This gulch has been formed by erosion and is still slowly extending its area. By reference to the geological map it is seen that the underlying rocks are of the same character on both sides. Whatever differences of soil, therefore, are observable at the present time are not to be referred to original differences of the rocks, but are due to changes incident to its gradual formation, such, for example, as the accumulation of vegetable mold on the shady side. A comparison of the photographs of the two sides of the gulch Ai points directly opposite (plates 9 and 10) shows at a glance some of the more striking differences in their plant covering. The sahuaros, which are a most conspicuous feature on the right side, facing west of south, are hardly seen on the opposite side, and the same is true of Encelza farinosa. On the other hand, there are various plants on the shady (left) side which are either very meagerly represented on the right or are not found there at all. For the purpose of more exact floristic comparison of the two slopes, six areas of 100 square meters each were located, three on each side of the gulch and as nearly opposite as practicable, and a careful enumera- tion made of the perennial species of plants growing upon them. Peren- nials alone were counted, for the reason that they constitute the more permanent vegetation, though the annuals present the same general facts of distribution. The use of such marked areas gives a fairer com- parison than would a collection at large, though the latter would increase the number of recorded species. On these six areas the whole number of perennial species found on both sides of the gulch was 48, of which 24 were found on the right side and 39 on the left. The number of species within these areas common to both sides is 15. There were 9 species found on the right side which were not found on the left, and 24 on the left side not found on the right. The most significant fact is that upon these representative areas more than two and a half times as many species of perennials were discovered growing exclusively on the left bank with its northerly exposure than on the right bank of the gulch with its exposure to more severe desert conditions. Still more impressive is the great difference in number of individual plants. As already stated, certain species well represented here show no aspect preference; but with many the case is widely different, as is shown by the list of 10 characteristic species on the six marked areas. (See table 1 on page 44.) 44 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. TABLE 1.—Characteristic species on the marked areas. No. of indi- No. of indi- : viduals. . viduals. Species. Species. Right.) Left. Right.| Left. Encelia farindsa,.. ee eee | 1r2 3 Spheralcea pedata....... 4 a7 Cereus giganteus sae. 45 eS) O Brickellia-‘coultera.. 22 & « 4 28 Menodora scabra 2 aa 12 94 Lippia wright see yas O 2 ADUtUON CHSp Mie ye eee 14 O Brodiza capitata......... O IIO A Mcanuniye. ee. ae eee oO 52 Janusia gracilis soe) .&.. > II 86 A comparison of the annuals, especially as regards numbers of indi- viduals, would be still more striking. When the winter annuals are in their prime, those on the right bank make no impression on the eye from the opposite side, while by reversing one’s position and looking over on to the left side from a point near the Laboratory, its whole face appears covered with a rank growth of annuals. There is an apparent lack of good soil on the right side, but none the less there are many spots where there is good soil that is unoccupied, or almost unoccupied, by plants. This condition of affairs has evidently come about gradually. Humus has slowly accumulated on the left side of the gulch, and the conditions have improved from year to year for the growth of plants, but the original difference of the two sides is one of aspect, and it is this that is to be regarded as the primary cause of the great differences in their vegetation. We may, therefore, consider aspect, or direction of slope, from a purely physical point of view, as the essential cause from which, as a starting- point, the differences of condition and of vegetation already noted have taken the form which they exhibit to-day. Originally and fundamen- tally, the difference between the two sides of the gulch is simply one of insolation, a difference that may be expressed in physical measurements. It was thought worth while, therefore, to make a series of temperature records for a period of some months. ‘These were begun December 17, 1906, and brought to an end May 20, 1907. Measurements of light inten- sity and readings of wet and dry bulb thermometers were also made during a part of this period, and reference will be made to these later. For the temperature records four sets of instruments were employed, namely, two registered maximum and minimum thermometers for soil temperatures; four ordinary soil thermometers; a number of black-bulb thermometers, and a set of standard U. S. Weather Bureau thermom- eters for air-temperatures, all of which were tested and compared at the beginning and during the progress of the work. ‘Two stations were established on opposite sides of the gulch at points where extreme con- ditions prevail; that on the right side being exposed to full sunlight nearly all day, while that on the left was backed by a wall of rocks and was well shaded. The maximum and minimum thermometers first men- ~ LOCAI, DISTRIBUTION OF SPECIES. 45 tioned were placed in galvanized-iron tubes and sunk in the earth so that the sensitive bulb was 1 foot below the surface of the ground, the space above it being filled with a plug of earth, also inclosed in a galvanized- iron tube, so as to secure readings representing as closely as possible the temperatures at that depth. They were also placed, during a portion of the period of observation, with the bulb an inch below the surface. The ordinary soil thermometers were placed so that the bulbs were 2 inches below the surface. Two of these were employed, one in full light and the other in shade, at each station. The black-bulb thermometers were placed with the bulb 1 to 2 inches above ground, and readings were taken in full sunlight and in shade at each station. The Weather Bureau maximum and minimum thermometers were set up for comparison at each station, each being artificially shaded. The readings taken during the period of observation are too volumi- nous for record here, but are given in part, on p. 98, in the section on climatic conditions. Only the more important results will be given in this place. (1) Minimum and maximum soil thermometers, bulb at depth of 1 foot: (a) During the period of observations in December the average mini- mum and maximum were, for station I, 54° and 57° F. and for station II, 49° and 49.5° F.; that is, the minimum at station I, averaged 5° and the maximum 7.5° higher than at station II.! (6) In May, during the period of observation, the average minimum and maximum for station I were 74.5° and 80° F., and for station II 70.5° and 73° F.; the minimum at station I averaged 4° and the maxi- mum 7° F. higher than at station II. (c) The difference between minimum and maximum at station I was from 2° to 3.5° F. in December, and from 4° to 7° F. in May, while for station II the corresponding differences were 0.5° in December and 1° to 4° in May. (2) Minimum and maximum soil thermometers, bulb at depth of 1 inch below the surface. The observations recorded in March, April, and May, table 7, with the bulb 1 inch below the surface, show, as would be expected, a far wider range of temperature. (a) The average minimum and maximum at station I were 62.5° and 95° F., and at station II 60° and 70° F. (6) The difference between minimum and maximum readings at station -I ranged from 30° (March 29) to 40° F. (March 25). At station II the difference ranged from 6.5° (April 12) to 13° F. (March 29). (c) While the minimum at station I averaged only 2.5° higher than at station II, the maximum averaged 25° F. higher. 1Slight apparent discrepancies in these averages are due to the fact that they are derived from a larger number of temperature records than are given in tables 8 to 10, p..98. 46 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. These observations were supplemented by many others taken with the ordinary soil thermometers at a depth of 2 inches below the surface. Readings of these were made from January 25 to May 20, 1907. Within this period the lowest and highest readings at station I were 62° and 119° F., and at station II 54° and 112° F., the lowest in each case being in the shade and the highest in the sun. It is to be observed that whether in sun or shade, the temperature of the soil at a depth of 2 inches was always higher at station I than at station II. The difference on some cloudy days was no more than 3°, but on sunshiny days a difference of 10° to 15° F. was frequently noted, and in some cases as much as 20° COV25 0? Readings of the black-bulb thermometer were made from January 26 to May 20, 1907, the temperature being taken at 1 to 2 inches above the surface, in nearly all cases in the middle of the afternoon, but part of those in April and May at about 10 a. m. From the table on page 98 it is seen that: (a) The temperature of the air at 1 or 2 inches above the surface, from January 26 to May 20, averaged about 3° higher at station I than at station II (readings in each case in the shade), but frequently the difference was as much as from 8° to 12° F, (6) Differences in readings at points in sun and in shade on either side of the gulch are nearly the same, running much of the time from January 26 to May 20, between 20° and 35° F., though coming up several times to 40° and in one instance to 42° F. Summarizing the observations of temperature for the two sides of the gulch, it appears that on the right side, with southerly exposure, the soil temperatures have a much wider range than on the opposite side and in the daytime are much higher, the average observed maximum for 3 months being some 22° F. higher than that of the left side at a depth of 1 inch. These differences become less at greater depths, but still at a depth of 1 foot the soil is from 4° to 7° F. warmer on the right than it is on the left side, the difference being greater in winter than in summer. The roots of plants growing on the right side of the gulch, except as they penetrate to considerable depths, are in a soil always warmer, and in the winter, in the daytime, very much warmer, than that of the left side, but they are also exposed to much greater extremes of temperature. The air temperatures (in the shade) are also higher by 5° or more on the right side than on the left (often much more), but the greatest dif- ferences of temperature on either side are those of full sunlight and shade, running from January to May for the most part between 20° and 40° F. As the left side is the shady and the right side is the sunny one, during all the cold months of the year, these differences are greatly in favor of plants sensitive to cold that grow on the right side. When the sun is LOCAL DISTRIBUTION OF SPECIES. 47 high in summer the differences are less marked, but perhaps are no less significant as regards plants growing on the north exposure which are sensitive to extreme desert conditions. It is evident that, starting with temperature as the initial factor, semi- tropical desert conditions are distinctly emphasized on the right side of the gulch, and that these conditions are greatly mitigated on the left, and it can not be doubted that the great differences of their plant covering are directly correlated with these differences of temperature and the changed conditions to which they have given rise. As already stated, observations of light intensity and readings of wet and dry bulb thermometers were carried on for some time; but with the growing conviction that with our present methods no satisfactory results could be looked for, and with increasing evidence that, for such a compar- ison of habitats, light intensity at least, is a matter of very subordinate importance. This part of the work is accordingly not reported here. MEANS AND AGENCIES OF DISPERSAL. The various plant species of Tumamoc Hill are provided with means of seed dispersal essentially the same as those found in all great conti- nental areas of the globe. The pappus-bearing composites, which are fairly numerous, are adapted to wind dispersal; many others, including species of Boraginaceze, Umbelliferae, etc., have spiny or hooked fruits; others, such as Lycium, Celtts, and the cacti, have fleshy fruits likely to insure dispersal through the agency of birds and other animals, and to these are to be added various capsular fruits, grasses with twisted awns, and still other mechanical contrivances of various degrees of effi- ciency in local dissemination. Of the several agencies of dispersal, the strong winds of the desert rank high in efficiency, and there is no doubt that light, winged seeds are borne on the wind to great distances. Exact observations are, in the nature of the case, difficult to obtain, but the evidence is ample. Taking 25 or 30 miles as a measure, far within the limits of safety, of the possible annual advance of a species with light seeds adapted to wind dispersal, it is certain that in a few years such species may have migrated hundreds of miles from their point of departure. Indeed, it can not be doubted that their geographical limits are imposed by environmental conditions rather than by means of dispersal. Given the time element, there is no -part of western America, in which suitable conditions prevail, which such species may not reach. Their present actual range may, therefore, be looked upon as a resultant of a number of different factors, the deter- mination of which presents a most intricate biological problem, involving determination of capacity for dissemination, often practically unlimited except by natural barriers, and the controlling influence of the most diverse natural environments. 4S DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. Much the same, though with certain obvious limitations, may be said of the species that are disseminated by the agency of birds. The well- known fact that some birds migrate practically the whole length of the American continent, from beyond the Arctic Circle to Patagonia and return, indicates the possibilities in this direction. W. E. D. Scott has named 248 species of birds as occurring within the region extending 80 miles north and 40 miles south of Tucson, of which, aside from those ranging through the whole region, “common on the plains” or “among the giant cacti,’ and therefore to be counted in, no less than 69 are specifically mentioned as found in the vicinity of Tucson. (See Bailey, 1902.) When it is considered that this list includes ducks and other aquatic birds, doves, woodpeckers, jays, crows, and many other birds whose efficiency as distributors of seeds is well known, it is seen at once that the birds which visit Tumamoc Hill and the adjacent valleys are both numerous and active enough to count as a factor of prime importance as an agency of dissemination. Exact observations of species known to be introduced by their means are not easily made, but from what has been seen of the feeding on cactus fruits and mistletoe berries by wood- peckers, and the extent to which the seeds of various crucifers, plantains, and other annuals are eaten by various small birds common about the Desert Laboratory, it is perfectly certain that many species of plants now growing here are carried year after year, often to long distances, by birds, and presumably found their home here originally by the same ‘agency. According to Tuomey, “nearly a half hundred birds feed upon the fruit of the giant cactus, the list including all our thrashers, wood- peckers, finches, and pigeons.”’ But while birds function most conspicuously as disseminators of seed to the advantage of the species thus distributed, their relation to the vegetation of Tumamoc Hill is, in some few cases at least, unequivocally destructive. Thus the Gila woodpecker, Melanerpes uropygialis, makes large holes in the giant cacti by which the natural protection of the soft parts within is so far destroyed that decay, often involving the destruc- tion of the plant, ensues. A considerable number of mammals, conspicuous among which are jack-rabbits, squirrels, rats, and gophers, make their home on Tumamoc Hill or in its vicinity, and are in close relation to the vegetation either as active agents of seed dissemination or as destroyers, some of them playing a double réle very effectively. Squirrels here, as elsewhere (compare Bailey, 1905), fatten on the fruits of the bisnaga (Echinocactus wislizent), and these and other rodents are doubtless responsible to a very large extent for the transfer of various edible fruits and seeds to limited distances, and very likely assist materially in carrying from one point to another seeds that are provided with hooks and similar appen- ¢ LOCAL DISTRIBUTION OF SPECIES. 49 dages. Asa destructive agency, the mammals of this region are respon- sible for losses which would be far greater were it not for the extraordinary degree of protection which so large a proportion of desert plants enjoy. The jack-rabbit, when pinched by hunger, attacks the flat opuntias of the hill and manages, in spite of thorns and spicules, to gnaw out large portions of joints, the plant presenting an unsightly appearance as the result, though never, as far as observed, entirely destroyed. The part played by rodents in the dissemination of seeds on the Labor- atory domain has probably been far greater than at first sight appears. Following the unusually heavy rains of the winter of 1904-05 the palo verde (Parkinsonia microphylla) on Tumamoc Hill bore an abundant crop of seeds, but on my return to Tucson in the fall it was with difficulty that a mere handful of pods could be found. The seeds are unprovided with any special means of dissemination, except as they contain food- substances, and there is no other explanation of their disappearance so probable as that they have been carried away for food by rats and squirrels, which are often very numerous in the vicinity of the Laboratory. In times of protracted drought, too, these animals are seen, emboldened by hunger, to carry away every vestige of possible food left on the ground. Following the dry winter of 1903-04 it was noticed that the sparse growth of annuals hardly appeared above ground before it was closely cropped; so that normal growth was quite impossible, owing to the presence of numerous half-starved rodents in search of food of any kind, which was eagerly snatched, even when they were watched at close range. At such times the destructive work of these animals becomes, it would seem, a factor of considerable magnitude in limiting the spread of certain species; but from their great abundance in following years of rainfall, it does not appear that the life of any species has been threatened. In short, the probability is that, with the exception of the giant cactus, which suffers, as already stated, from the work of wood-peckers, there are few, if any, species on the Laboratory domain that have been ser1- ously interfered with by animals. The case, of course, is different on the flood-plain of the river, where overpasturing has induced great and irreparable losses, but these changes belong to those induced by human agency and fall into a separate category. Allin all, the mutual relations of plants and the larger animals here are, at the present time, distinc- tively advantageous to each. As far as pertains to strictly local distribution, it is clear that ants, which are numerous both in species and individuals, are highly efficient agents. They are seen on all parts of the Laboratory domain, busily engaged in gathering seeds of various plants and carrying them to their quarters. Seeds of the following genera, thus carried by ants, have been identified: Microserts, Plantago, Lesquerella, Harpagonella, Cryptanthe, Daucus, Amsinckia, Festuca, Ervophyllum. 50 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. The number of plants on the Laboratory domain that are provided with hooks, spines, etc., is relatively large. At certain seasons of the year it is almost impossible to walk about on Tumamoc Hill without carrying on one’s clothing a collection of burs of Harpagonella, the siliques of Thelypodium lastophyllum, or the equally tenacious fruits of other genera. ‘The seeds of such plants are distributed in great numbers by domestic animals, and doubtless by others whose part in transportation is less easily observed. The part played by domestic animals is perhaps most conspicuously shown by the ubiquitous cocklebur, which, from Texas through New Mexico and Arizona to California, has crowded into roadsides, river-bottoms, and waste lands generally, and is everywhere seen with its prickly burs matting the tails of horses and cattle, and constantly carried by them to whatever fresh spots have not yet been invaded. ios PGP Oc wal ee YS Ob At ‘shee *. i age ep tale é — y = Ay ' 4 - — ‘ ome + tT, A, SPALDING PLATE 21 Permanently marked area No. 7, showing invasion of Erodium cicutarium. In center of area a large individual of Parkinsonia microphylla. Anchoring roots of a sahuaro, measuring 6.8 meters high and 39 cm. in diameter at the base. CAMPBELL ART CO., ELIZABETH, N. J. Pies) es ae bys ie ee LOCAL DISTRIBUTION OF SPECIES. 5a nN) w aN on o N 0 © ro) ore loreal islet tele beieiol ele ra 21 ERE ESEORS EAE EEECEEEEEEEEEEEEEEEEE EEE CoeEEEE Eo Pele beiaes grey aie ere ee ere loterat erebeelnt | feb ee Tear (Se Le ea So. GSP Reon SC ea aee URC Ta eaeo om ee eeeeoRaeeae . ; : SGGGa Sid vitae taba els aie eis bl aeee onele bla ialy lal Toll ren 6 |_| A eee emaatemereamce i ete eer tr wood NICS IVT SLUG LL ONC ee ieee ere srel never rast rer te ietetet tte Poy tet to 4 Sassen eee tere siere (Sie nel ieee eh) at ds) meooes ry 3) 5 nag eamoame? eee ee eee ee er cley eee sie ee ea papet eet re Pt et de heb Hots de. CCOBe eo Ceeeeeaaneee Le nn Liebe a iet al sd Re eames ea EoBEe Cann" HAAR RCL ARE Se aes RRA S) 17. aes See a eae opti stetereispe ete fel a PT ry ae a a i x | | Lie Ae pte eRe ieee isle eG Teh teh eT hs rn PEELE EEC EEEEEEEE EEE CEE EE CEE epee SPSS UNS eT reel er ee ees Pe Peet ial weep eiet febeioio |eintetpettcle palette Feber aha bel ite ee ep nd ee feleiot dae pale tellin tt Ie) ot Bod mogascees ee he N Re eg HEE + IL Zo I | SaBEGK Ra tey eet ede Bega ERBEGNAISaAReRReA SCE ED PELLET BABES US UEROR SMMC Ges EHC eoue © ane mmaaie ) Oa ns a ES SE EERE erates el belo) sb ehaln ds teh te ei Dit 2h Sa EPEC E a ee pe ee Ct eerie tbat ere RaS2ee2=2 | & ARO ZEMER ARSE EEEEEEE TEEPE EEE EH PERE Acer Erte GE SAR et PR TST Pe teicher Pia fis | ope Pn fois LF | RECUR ISRaNS a ieee el tet talet a Leh eis bel 4 ede ta eee Ace ree tel ebooks CEEEBEEE EEE SEEEE EEC EAE eee ps penceneeee cau ssues ecueveses Geeed Setececeeeeeaz Lime Se ee Pa ay | Siero erase ie yee ep ore ee eye eye Te ia ed EOEED ESET UGEaUeCEEEC SEEEOGEUES PST EESETaceaTas 8 Kaun ie SRENae coc euoeonaeeeceooeecoee : | | | — Ltt tL | ill Fre. 3; Area including 100 square meters, showing position of perennials (marked by a cross with initials of name) and alfilaria (marked by dots), February 21, 1906. Ac, Acacia constricta; Bh, Bigelowia hartwegwi; Ce, Calliandra eriophylla; Ds, Delphiniwim sca po- sum; Fd, Franseria deltoidea; Lb, Lycium berlandieri; Ov, Opuntia versicolor; Pm, Parkin- sonia microphylla; P, Philibertia sp.; Sp, Spheraicea pedata, As indicated by plate 22, 13 small patches were located, all of them at no great distance from the Laboratory building. Very probably a few other spots were occupied at that time by this grass, but if so, the essential fact remains that the points mapped include all that were readily found and represent, with substantial truthfulness, the very early stage of invasion then observed. As in the case of Erodiwm cicutarium, details of distribution are included in the Laboratory records for the purpose of reference in further observation of the invasion of this species. Invasion of many other species on Tumamoc Hill and in the adjacent valleys has taken place and is still going on. On the flood-plain near the river are extensive areas so covered with Xanthiwm canadense and Malva parviflora as to nearly obliterate all trace of the original vegetation. Along paths in the vicinity of the Laboratory Monolepis nuttalliana has 54 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. taken complete possession of limited areas, and in spots where water has been used close to the building, Bermuda grass has made its appear- ance within the past year. Numerous other weeds, chiefly annuals, have come to occupy, more or less conspicuously, such ground as they have found available, especially on the flood-plain. While, as indicated, annuals and foreign weeds are most prominent as invaders, there are various perennials, particularly certain species of grasses, which present every appearance of invasion, either successfully accomplished or in progress. Among these are Hilaria mutica, and H. cenchroides, which, on the north slope of Tumamoc Hill, occupy extensive patches in the midst of other vegetation which they are apparently displacing. In order to determine this fact definitely, a number of permanently marked areas have been established for the pur- pose of continuous observation for a period of years, and maps and photo- graphs of these are kept in the records of the Desert Laboratory. In general, it appears that on the flood-plain the invasion of various species has resulted in their almost complete occupation of extended areas, so that the vegetation of these areas is essentially different from what it was in earlier days; but no such radical change is observable on Tumamoc Hill and the slopes adjacent. The invaders of the plain have taken advantage of changes effected by the hand of man. They found a fertile soil not fully occupied, and took possession with a thorough- ness that seems likely to be successful against competition for an indefinite period. On the hill and slopes, on the contrary, no such preparation for their invasion has ever been made, except to a limited extent in road- making, and their advance has been relatively slow and inconspicuous. Thus far the discussion has chiefly involved introduced weeds, but certain indigenous species have a history in some respects quite similar. One of the most interesting of these cases is that of Bigelowia hartwegit. On the flood-plain and adjacent slopes, this plant has been observed within recent years, almost covering the ground where before it was relatively inconspicuous. ‘This, according to Thornber, seems to have been closely connected with a period of abundant and well-distributed rains during the year 1905 and several months of the preceding and following years. During this period rain fell in sufficient quantities to insure the growth of large numbers of seedlings, which became well established and at the time of special observation in April, 1906, were apparently well beyond the critical period. At that time the parent plants could be observed quite scattering and several times larger than the seedlings of the new crop, while between them the young plants almost covered the ground and have ever since maintained the foothold then acquired. The various invasions that have taken place on Tumamoc Hill and in the adjacent valleys have necessarily involved competition. It is > Hien | fa 6 to EY ae bis «als ee Bae . ea er Te i Loic iff Is nthe ce a ee .- —_ ¥ ag —— 2 ey, eel pe ee ef a 2 PLATE 20 0 14 | \ uh : ‘% (kes es Ft Wood vik | BN ere noo BNL de | 2 i ee: 1s Hod Eanes cee Vi v7 ‘A ' is | vA } bigs a a id > A] o ' aS z j eo © | w+ © 5° SS Ss 2 =z tw O = i | eo a & | \ - a es ee ee eee | { be ff eae ve =~ lf #\\ }! / a ll ale § ———-. | \Y | i i { { ~ ie — ——__ ( \ j = \ / A ee r / igi: Se ANN | \ Ae ee a eo ae \ AN \ / i V Lod / wo aN SS | \ / | se fr & | oO iV\ SN \ \ i Ds \ a . \ f il q ’ \ \ a =\\ \ Sli NW \ / ZA | : Sr a Se a S SE \ \ aS | St \ . ac eas on ee \\ aS | Se ee oe ee em \ eo g(a ga ee ae ee a ae a \ | a ea orm Oe ey ee ee et eee, ee a EN ia BN Ss A AHA LH 4 + 4 -) - - \ Z a, ys E ST. MARY'S HOSPITAL ee eh Zz 7 q 462 eae ea { / | Stee | a ‘4 | ee Tl Feet see SANT a a . aot Ta vey & = - ee a ae + ~ | ; \ / ; era, y | J f me : | / f \ ‘eed \ | pies U/ | hd iy rat Wen eee It is scarcely necessary to refer to the Asiatic expeditions of the Carnegie Institution of Washington as the best example of a critical study of glacial, fluviatile, and lacustrine deposits which has developed climatic deductions of great importance. A moment’s consideration will show that a relation exists between climate and erosion and deposition, but that this relation is not simple. For example, deposits piled at the foot of a mountain of considerable height will resemble in some particulars those formed at the foot of hills under the intense atmospheric and torrential action of a more arid cli- mate. Still further, climate itself is a complex, not a simple factor. Assume, for instance, a certain moderate number of inches of rainfall and then increase the temperature, and one discovers that the gentle erosion retarded by a covering of vegetation gives place to the intensive erosional and depositional action of the semi-arid climate. Again, by *Davis, W. M.: Is the Denver Formation lacustrine or fluviatile? Science, n. S., VI, 619. “Walther, J.: Einleitung in die Geologie, 1904. *Grabau, A. W.: Types of sedimentary overlap, Bull. Geol. Soc. Am., xv: 567-636, 1906. Barrell, Joseph: Origin and significance of the Mauch Chunk shale, Bull. Geol. soc! Ani, XVIN, 449-476. Barrell, Joseph: Relative importance of continental, lit- toral and marine sedimentation, Jour. Geol., xrv, 316-356, 430-459, 524-568, 1906. *Chamberlin and Salisbury: Geology, 3, 193-194, 196-215, 243-248, 258-276, 296-318, 472-483. Baers especially, Ellsworth Huntington: Some characteristics of the glacial period in non-glaciated regions, Buli. Geol. Soc. Am., XVIII, 351-388. ENVIRONMENTAL AND HISTORICAL FACTORS. 69 lowering the temperature, the disruptive action of frost and the repres- sion of vegetation may under certain conditions develop intensive action. It does not seem probable, therefore, that theoretical analysis of the complex relations that obtain between climate and deposition will accoim- plish what it has in the case of deposition by running water or by glacial action. The problem will be solved by detailed studies in each region. In each case the disturbing factors must be evaluated and the intensity of each process gaged.! IDEAL SECTION THROUGH A PLAYA A= Angle of rock surface ” 4 erosloTe B= C= 4 4 slope deposition % Fic. 3. One of the most inviting fields for such a study is the “bolson”’ or undrained area developed under conditions of aridity. The typical bolson? is an expression of aggradational processes and is excellently portrayed in the smaller undrained flats of southwestern Arizona. An idealized section through a bolson is attempted in figure 3. The angle A represents the slope of the top of the mountain chain or peak. This upper surface is often parallel to the rock structure and is therefore flat or sloping as the strata are horizontal or inclined. The higher moun- tains reach up into a region of forests and abundant grasses which pro- tect the surface and preserve the flat top. The angle B is the slope developed by the attack of torrential precipitation upon the rock struc- 1Since writing the above I have received the Journal of Geology, xvi, No. 2, which contains the first installment of an article under the title ‘‘Relation between climate and terrestrial deposits,’ which is to be continued in Nos. 3 and 4. It appears that Professor Barrell has not been deterred by the difficulties inherent in any general anal- ysis of the relations between climate and deposition. The portion published indicates clearly the great value of his contribution, and the completion of his article is awaited with impatience. 2Hill, R. T.: Topog. Atlas of the U. S., Folio 3, U. Se Gra tooo.) Kmever: Cas. Bolson plains and the condition of their existence, Am. Geol., xxxIv, 160-164. Tight, W.G.: Bolson plains of the southwest, Am. Geol., XxxXv, 271-284. 70 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. ture. It is therefore a function of both rock composition and structure and of climate. Strange to say, erosional attack is given strongest topo- graphical expression in regions of very scanty rainfall, where the torrent of every dozen years takes everything before it (plate 25). Slope C is the most striking and typical of the topographical features of the semi- arid regions, and not only the larger ranges surrounding the bolson, but also each little individual hill appears, as it were, mounted on a sloping pedestal (plate 25). These slopes have often been described.’ Herrick? has aptly named the extensive slopes of low gradient in New Mexico “clinoplains,’’ and Ogalvie® has called the talus apron of the individual hills “conoplains.”’ While these names have much to commend them, there seems to be a need for a simple term for this extensively developed topographic feature, a name that will go with such apt and commonly accepted terms as mesa, playa, bolson, etc. I therefore suggest the term slope for the inclined plain, and the word wash to cover the various forms of outwash deposited on the slope. It would not be necessary to emphasize the subaerial nature of the wash- deposits of the slopes, were it not for the fact that erroneous interpre- tation has recently been given them. They are without question the depositional phase of the erosional activities above. Running water plays a varying role, having no part in the formation of the symmetrical slopes under certain arid conditions, temperature change and gravity alone being involved. Except for the steepening of the angle close to the base of the mountains, these plains keep their even gradient sometimes for miles (plate 25). The undrained flat in the center is the playa. With increased pre- cipitation or decreased evaporation it becomes a lake. Its material is almost entirely wind-blown, deposition being most active during periods of water occupancy, when the dust from the mountains and slopes is caught by the water-sheet. In bolson topography there are all gradations, from those showing marked development of these features to those in which some of the features can scarcely be recognized, on account of milder climatic con- ditions, partial drainage by some master stream that has conquered the desert conditions, or the lack of the tectonic features necessary to initiate the cycle. It needs but a cursory investigation to suggest that the past climate can be read, provided that the deposits laid down in the center of the bolson under the varying conditions of no water (desert flat), playa, and expanding and contracting water-sheet can be separated from the sur- “Blake, W. P.: Some salient features in the geology of Arizona, etc., Am. Geol., XXVII, 167. * Herrick, C. L.: The clinoplains of the Rio Grande, Am. Geol., xxxrv, 376-381. *Ogalvie, L. H.: The high altitude conoplain, Am. Geol. xxxvI, 27-34. SPALDING PLATE 25 Volcanic hills in great basin, near Hazen, Nevada. Typical slope west end of Santa Catalina Mountains from the north. CAMPBELL ART CO,, ELIZABETH, N. J. x pele ae vr a ) e, « oe. t ¢ THE LIBRARY OF ak ae ee WHIVERSITY GF ELLINGIS | ENVIRONMENTAL AND HISTORICAL FACTORS. it rounding wash-deposits of the slopes. The studies now in progress suggest that the critical line between erosion (above) and deposition (below) is a function of climate. It is a fact that in many cases the upper edges of the slopes are being dissected. Here, however, the changes are more complicated than in the former case. I shall content myself with the presentation without discussion, of a bare list of the criteria I have found to be available in this special case to distinguish the two kinds of deposits. I shall only consider particu- lars in the physical characteristics and shall omit differences in chemical composition and fossil content, which have been discussed in the litera- ture of the subject. . I have been asked for a statement concerning the origin of “caliche,”’ in the light of recent studies in the vicinity of Tucson. Little can be added in the way of description to the excellent account of Dr. Blake.! He applies the name to the surface crust, mainly of lime carbonate, that develops under the conditions of mild aridity in Arizona and northern Mexico. I think that this definition should be followed, and as suggested by Lee the term ‘‘cement’’ be applied’ to the crystalline matrix of the desert fill, a crystalline, calcareous cement-conglomerate, often containing considerable amounts of selenite and hyalite, and a strongly gelatinizing silicate, probably a zeolite. Dr. Blake assigns the source of the caliche to the ground-water drawn upward to the surface by capillary action and evaporated there, finding support for this conclusion in the fact that the well waters in the vicinity of Tucson are charged with the mineral constituents of the caliche. The conclusions of Dr. Blake have been verified by Ransome’ for the vicinity of Bisbee, and by Lee* for certain deposits in the Salt River Valley. While it is not impossible that this explanation may fit certain cases where the water-level stands within a few feet of the surface, it certainly can not be applied to the Tucson region to meet whose conditions the hypothesis was framed. Here, where the caliche is thickest, the water- level is from 60 to 120 feet below the surface, and it is a well-known fact that in fine soils capillary action can only develop a head from 6 to 12 feet. Furthermore, in all observed cases where the ground-water stands close enough to the surface to furnish a supply for evaporation, the sol- uble- alkali salts and not caliche are deposited. 1 Blake, W. P.: The caliche of southern Arizona, etc., Am. Inst. Mng. Engs., XxxI, —220. : ; She W. T.: Underground waters of the Salt River Valley. Water Sup. Papers, Pe, INO: 136. ; ; Se B. ie The Geology and Ore Deposits of the Bisbee Quadrangle, Arizona. Prof. Paper 21, U.S. G.5., 74. Sree a Welt slic, TT. 72 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. TABLE 2.—Particulars in Physical Structure which may be used to Separate Wash, Playa, and Lake Deposits. The wash deposits. The playa deposits. The lake deposits. Stratification. (1) Stratification developed. very strongly (2) Rapid variations in coarse and fine material in both a vertical direction and in a direction of the strike. (3) Bowlders in matrix sand or clay. (4) Thin layers of flattened, pol- ished pebbles overlying dust or clay. (Indicates accentuated arid conditions.) (5) Plunging stratification, small pockets of perfectly sorted sand, trains of coarse material, varying in size up to bowlders 1o feet in diameter; all developed in the courses of the transient torren- tial streams. Sizé of material. Torrential drainage often has the capacity to carry bowlders to to 20 feet in diameter. Distribution of coarse and fine. Coarse in the upper edge of the de- posits fringing the mountains and reaching far down in the stream channels, The upper limt. The upper margin does not lie ina horizontal line. It extends up the valleys. Shape of constituents. The bowlders are angular and semi- rounded. Slope. Increase with approach to source, farther out very regular. This long regular slope is not dupli- cated in any other kind of depo- sition, Other phenomena. Wind ripples often developed in sandy layers. (1) Deposits of mud and clay without marked stratification. (2) Occasional layers of single thickness of flat- tened pebbles, fitted together and polished by the wind indicates pro- | longed desiccation. Very fine sand and clays. a) Si teparie 9 © ‘che yore) Wmeiey we Sige fours. 2 ae Deposit limited by a horizontal line, which fluctuates with every change in the relation of precipitation toevap- oration. 1S Fe. oe wien ew 6) ei he Wel a) a Keen, ove at Sure te Sole Practically horizontal. Mud cracks, fossil prints, etc. (1) Stratification marked at margin and showing less development away from shore. (2) Typical shore forms and stratification due to shore action. | (3) Deposits sorted to a _ uniform size. This is never accomplished in wash deposits except in local pockets in the larger stream courses. Material larger than cob- ble not common. At the shore-line. Bounded by a horizontal line along which may develop the erosional features of the shore- line. Bowlders are rounded or semi-rounded. Decided slope only at shore-line and then not equaling that of the wash. Sand dunes can only de- velop to any amount where there is perfectly sorted beach sand to furnish the material. ENVIRONMENTAL AND HISTORICAL FACTORS. 73 Professor Forbes, of the Agricultural Experiment Station of the Uni- versity of Arizona, has kindly given me the following statement of his conception of the origin of the caliche: Caliche is a mixture of (probably) colloidal clay and carbonate (mainly) of lime. These two constituents, one in solution in the carbonated rain-water, and the other in suspension, are carried from the surface of the desert soils to the depth to which occasional rain pene- trates, which in this region varies from a fewinchesto3or4feet. At the general average level at which the wetted soil dries out through the desiccating action of an arid atmos- phere a more or less compact caliche stratum is formed. In situations where the soil surface is filled in from time to time new caliche strata are formed below each new soil level, the more recent formation therefore being above, the older below, in such sec- tions as are revealed by well-borings near Tucson. This explanation with some modifications will account for the occur- rences I have observed. Professor Forbes recognizes only the descending percolation of the water, but there is often a subsequent drawing to the surface by evaporation, whenever the drying out of a soil after a rainfall overtakes the downward percolation of the water, and taps the reservoir of moisture that is retained, even under arid conditions, just under the porous soil surface. To develop crusts there must be some ready supply of calcareous matter, and therefore no active underground drainage to remove the same. In the case of the Tumamoc Hills the source is the igneous rocks, especially the amygdaloidal cavities, as described later. In the vicinity of Tucson, the widely distributed Paleozoic limestones were the original source of much of the calcareous cement of the fill. As the gravel deposits are accumulated the caliche layers are built into them and slowly recrystallized by the percolation of the deeper waters. The development of the caliche is a rapid process, and in this it is in keeping with the acceleration of geologic action under aridity. In one place under observation the caliche was broken up and mixed with lime and brick left after building operations, and the mixture leveled and packed. No vegetation was allowed to grow and the ground was flooded frequently to keep the surface packed and lay the dust, etc. Within two years’ time there had developed 2 inches of typical caliche crust within half an inch of the surface. In other places, where the ground was not flooded, the new caliche is recognized with difficulty. The body of this article is divided into three divisions, viz, Topography, Geology, and Petrography. Prof. F. N. Guild’ published a microscopic description of the rocks of this area in 1905. He has kindly consented to examine some new material and revise his descriptions. His contri- bution appears under the head “ Petrography.” TOPOGRAPHY. The largest of the group of three hills already mentioned has been rechristened with its old Indian name, Tumamoc, by the staff of the Desert Laboratory. It was formerly known as Turtleback. Of the two *Guild, F. N.: Petrography of the Tucson Mountains, Am. Geol., Xx, 313-318. 74 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. smaller hills the most easterly of the group is Sentinel Hill and the third, which is a ridge between the two, is unnamed. ‘Topographic analysis leads to the following divisions, which will be described in order. (1) The Tucson Mountain Slope.—This extensive slope reaches down from the Tucson Mountains several miles to the west. It comprises more than half of the height of the range above the Santa Cruz River, to which it descends. (2) The Tumamoc Hill Slope-—The Tucson Mountain slope passes under the superposed Tumamoc Hill slope. The two meet on a line marked approximately by the main gully southwest of Tumamoc Hill. The lower limit of this slope is well defined on three sides by sharp con- tact with the Tucson Mountain slope, and on the east by the Santa Cruz alluvial flat. The upper limit, however, practically defies definite limi- tation, culminating in irregular talus slopes reaching up to the top of the hill in places, while again the lava rock extends down to the Tucson Mountain slope or the alluvium. (3) The rock surjace——This can not always be separated from the débris-built slope, as there is more or less volcanic rubbish, even on the tops of the hills. In all the hills it has a moderate dip toward the north, but faces the south with a much steeper declivity, developing small cliffs. The northern rock surface is diversified in a minor way by small hum- mocks 5 or 1o feet high, formed by a turning-up of the edges of the cooled surface of the lava by a second movement. Talus patches lie below these cliffs. (4) The alluval plain.—This is the product of the Santa Cruz “ River,” a small intermittent stream (over 100 miles in length, however), which until a few years ago was in the depositional stage, but, aided by an abandoned ditch, succeeded in starting a new cut which it is now extend- ing southward. GEOLOGY. The Tumamoc Hills are the product of the final (probably Quaternary) stage of the extensive Tertiary volcanic activity of this portion of Ari- zona. The interesting features are presented within an area of about 2 square miles in the immediate vicinity of the above-mentioned hills. Originally most of the surface was mantled with a covering of volcanic blocks, averaging roughly between 6 inches and 3 feet in diameter, and under those conditions the first impression would have been that the hills were formed by explosive action. The industry of the Mexican teamsters who have transported most of the surface covering to Tucson, where it is in demand for foundation purposes, has developed unusual facilities for observation, the results of which suggest that many of the déebris-choked lava’ hills have a more interesting and complicated struc- ture than is suggested by their exterior. With the accompanying topo- graphical and geological maps (plates 26 and 27) before the eye, it seems a ad aaa Ran Pale hs vor ee ie We pa Pe zy) -— i ‘, \ f 7: . : ‘3 Qe 7 fe 1 > + jhe i ot hy a ih, ¢ f my nal ags a . : ef STAs a rho ae? iy i ¥ ay es A ; ae 1 dia ae J ; a 7 +) ip" se 7 i ’ } aie piri iat AT r ; ; i MOR G | . * . o. ae | N? D . \ x ; ’ J | : | . maT ; “y ri " ~ +6 | naga eS halls 1 ie ee ae Ses , i tae “ rhe i st i "yj ii ; : ; Se +s a. i \ ‘f is ee beim NG i ene ots | ouvcanry AF wars i nie? tm > =)! F ‘ ‘ ' ; peg Or et a | ‘ete ine ae q ale ' . hal ee Gl a WS ae Rtn 9) Cana : d | a ; 4 a ) > A aa t he 28S: 4 : os ; a qian, *% hi daca i PRR Hie PLATE: 26 LEGEND o Soil Stations HOSPITAL O ) | | | | | | | | | | 7 apwhaes oo ae | | | | Ls ie ES PE — oh: ) - oa. =o. ina Surveyed October, 1906 -~ Cc. B. C! RESERVATION AND VICINITY OF THE DESERT BOTANICAL LABORATORY OF TUCSON, ARIZONA A HORN 8 CO BALTIMORE Wins Bias } Topographers | SCALE: 335 INCHES PER MILE wan é ENVIRONMENTAL AND HISTORICAL FACTORS. 5 unnecessary to describe in detail the distribution of the formation, or to divide the descriptions under the numerous subheads usually employed in the analysis of more extensive areas. I shall, therefore, combine in an informal way the development of the geological history of the region, with descriptions of the rocks, their outcrops, and their structural relations. The andesite flow.—The supposedly oldest rock of the Tucson volcanic series is an andesite, described microscopically as a “‘mica-andesite.”’ It is covered on the north, west, and south by rhyolite flows, is intruded by basaltic plugs, is covered by small separate basaltic flows in places along its eastern edge, is largely hidden under a covering of desert wash, and is bounded on the southeast by the Santa Cruz alluvium. The structure of the flow has not been deciphered. Its crystalline character suggests a very thick flow, or perhaps it is intrusive in part. It appears on three sides and underlies the basalts of the Tumamoc Hills. The rhyolite extrusions—The next event of the district was the outflow of many sheets of rhyolite. These are only recorded indirectly in the -region mapped by the pebbles in the later conglomerates. The back- bone of the Tucson Mountains consists of this rock, which includes not only typical rhyolite, and rhyolite breccia (the fragments of which are products of explosive action and foreign material picked up during the extrusive processes), but also all the grades between a vitreous rhyolite and a mud flow, the variations being formed by different mixtures of lava, ash, cinders, and superheated steam. Accurate estimates of the thickness of these flows can only be made after careful mapping on account of the extensive faulting, but it probably amounts to several thousand feet. The first period of faulting.—This period also is not registered in the portion mapped, the block-faulting being especially developed in the rhyolite flows. The faulting was regular, the blocks tilting in a north- easterly direction at an angle of about 20°, the fault scarps representing the broken edges facing southwest. The topographic effect of this frac- turing is noticeable from any point a few miles south of Tucson, the larger mountains (each a fault-block) showing the outline of an asym- metrical triangle. The intrusions and extrusions of the basalis—Next occurred a number of basic intrusions and flows, the history of which is somewhat varied in different localities, one phase of which is represented in the Tumamoc Hills. Here the first of the basic flows is a basalt, marked B, on the map (plate 27), and described under “Petrology” as plagioclase-basalt. It appears on the southeastern corner of the map, is well exposed along the Nogales road, and is noticeable on account of its large, glistening feldspars, some of which have measured up to 2 inches in diameter. The broken fragments of these feldspars, set in a dense cryptocrystalline groundmass, indicate plainly two outward movements of the mass, in 76 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. - the first of which the magma did not reach the surface, being stored in a reservoir long enough to develop the large crystals, and later was extruded as a viscous paste which did not flow far. There are a number of extrusions of this unusual rock within 50 miles of Tucson, indicating that this interrupted and renewed movement is a common phenomenon in the later igneous extrusions of the district. The structural relations, thickness, etc., are best shown in the sections A~B and G-H. ‘The source of the flow was probably south of Sentinel Hill, and it is not unlikely hidden under the alluvium in the downfaulted portion southeast of the indicated fault-line. The lower portion is somewhat scoriaceous, and the original upper surface of the lava was blown to small angular frag- ments (less than an inch in diameter) by the stream driven outward by the crystallization of the semiviscous mass. There are a few inches of this breecia preserved on top of the plagioclase-basalt by the next lava flow. Following closely, the intrusion of the neck B, and the correlated flow B, occurred, if my interpretations are correct. That the interval was short is shown by the accumulation of 80 feet of the plagioclase- basalt breccia on the top of B,, which was washed down from the surface of the plagioclase-basalt now covered by alluvium. Had this interval been long, this fragmented material would have been swept off from its exposed position on top of the plagioclase-basalt flow. The neck B, (the second variety of amygdaloidal basalt microscopically described) shows marked variation in both structure and composition. In the center and along the northern edge of the exposure it is coarsely crys- talline, assuming an andesite structure. In other places it is a very dense, heavy rock, entirely cryptocrystalline, considerably altered, the alteration products indicating the large iron content of the rock. In places the neck is brecciated and the fragments cemented with jasper, and again it contains masses of inflated scoriaceous material which decomposes into a red or yellow clay. The flow from the above center is the black basalt (B,) which covers a considerable portion of the map. It is the most basic rock of the sheet, containing olivine visible to the naked eye as brilliant red specks formed by alteration. It is classified as an olivine basalt. The structural relations are best shown in the section C—D. Following this flow there was a short pause in the volcanic activities and the neck suffered some erosion, and then the conglomerate was deposited (marked “older wash” and shown south of Tumamoc Hill). It is 100 feet in maximum thickness and is overlaid conformably by a thyolite-tuff 50 to 100 feet thick. At the time of its deposition the con- glomerate was the eastern edge of the Tucson slope, and where it was thickest it represents the bed of a temporary stream. Later it was faulted up to its present position. Its composition and structure reveal its torren- tial origin. It consists of beds of andesite and occasional basalt pebbles, in a matrix of fine andesite sand. In size the material ranges from small ENVIRONMENTAL AND HISTORICAL FACTORS. TT grains to bowlders 2 feet in diameter. The stratification is very well marked but has a tendency to wedge out in the direction of the strike. The individual layers vary in thickness from a small fraction of an inch to 5 feet. Igneous outbreak again records itself in the rhyolite-tuff mentioned above. It overlies the conglomerate south of Tumamoc Hill and the breccia in Sentinel Hill. Talus interferes with the determination of the extent of the separation of the tuff from the andesite and the basalts by the wash conglomerate. It is the most conspicuous formation of Ttumamoc and Sentinel Hills, appearing, when viewed from the south, as a white band and cap, in marked contrast from the reddish-black lavas (plate 1). It is composed entirely of products of explosive action—volcanic dust, glass, and pumice, the source of which was some unknown vent to the south. Wherever the conditions are favorable for its preservation, the Tucson Mountain slope contains similar deposits of tuff, indicating the extent of the explosive action. The deposit was largely eolian, and only to a slight extent a mud flow; the small size and small amount of inclusions, except those of pumiceous character, and the lack of stratifi- cation indicate wind as the chief agent of transportation and deposition. Very porous pumice occurs in fragments 3 inches in maximum length; the other fragments are of plagioclase and olivine basalt less than an inch in maximum length. The bottom layers are quite pumiceous, and the upper layers south of Tumamoc Hill are largely pure unconsolidated pumice. Again, some of the tuff is baked, recemented, and indurated, ringing clear under the blow of the hammer. In.color it varies from white through gray, drab, pink, and red. The portions of the tuff that are moderately indurated make an excellent building stone, light in weight and of moderate strength, but unsuitable for foundations, as it decomposes rapidly under the attack of moisture and the humic acids, doubtless due to the large per cent of alkalies it contains. (See analysis in the microscopic descriptions.) South of Tumamoc Hill to feet of conglomerate, similar to that underlying the tuff, is exposed and indicates a return to the ordinary wash deposition. Overlying the upper conglomerate and the tuff is the last of the lava flows, B; being similar in composition and appearance to the earlier flow B,. The direction of the flow was north and northeast. The platy-structure and reversal of dip is especially developed in this last flow, caused by a breaking of the first crust and a squeezing up of the viscous lava from underneath. The platy-structure is also formed without disturb- ance of the crust, developing whenever there has been a second movement in a semi-viscous layer. The reversal of dip is shown on the map by the sign (/-)and the dip of the formations by the conventional (|). It is not easy to determine the source from whence the last flow issued, but the considerable development of the platy-structure upon the top of 78 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. Tumamoc Hill, the reversal of dip toward its center, and the direction of the flow toward the north and northeast make it probable that the center is hidden under the body of the flow itself below the top of Tumamoc Hill. One of the noticeable features of these flows is their viscosity, thus differing from the ordinary liquid basaltic extrusions. This is the reason for the peculiar character of the final eruption, which was a swelling or piling out of viscous lava, and a consequent sealing of the conduit by the erupted material. This possibility is shown in section C—D by dotting in a theoretical plug. The description of the small intrusion marked B’, and described micro- scopically under the name of amygdaloidal basalt, has been delayed because there are few data to locate it in the history of the region. This was intruded into the andesite underlying basalt No. 3, and probably did not reach the surface. It will be found in the southeastern corner of the map. The only evidence bearing on the time of its intrusion is that both B, and B, are bent up around it, while the tuff does not show any change in dip. It is therefore probable that the intrusion occurred some time between the intrusion of B, and the deposition of the tuff. The second jaulting.—B, was extruded over what formed at that time a part of the Tucson Mountain slope, dipping at a gentle angle to the north- east. The flow extended as far east as the summit of Sentinel Hill (as- suming that the upper basalt covering the summit of the peak is a part .of this flow.) Subsequently the basalt and the underlying tuff were eroded from the area between the two hills. If the alternate hypothesis is cor- rect, that this patch of basalt marks a separate center of eruption, the lava overflowing to the north over the tuff, for which there is evidence somewhat similar to that suggesting a center under Tumamoc Hill, but little erosion need be postulated between the eruption of B; and the faulting which gave the hills their present form. The existence of faulting is discovered by indirect evidence, as I was not able to locate the walls of the break at any point. Some of the evi- dence bearing on this is the elevation of both the conglomerate and the tuff above the level at which they lie to the west; the sharp cliffs that separate the basalt and tuff from the underlying andesite on the south and east sides of the hill; the cliffs and truncated formations facing the Santa Cruz River on the southeast, etc. The fault around the small center hill is indicated by the perpendicular cliffs of basalt underlying the tuff on the south and west sides of the hill, and by finding a remnant of tuff and underlying andesite-conglomerate in the arroyo bottom, from which position it has been faulted up as shown in section E-F. Some idea of the time that has elapsed since the faulting can be ob- tained by an examination of the fringe of talus conglomerate cemented by caliche which surrounds the hill. The torrential precipitation aided by steep slope and gravity has no trouble in handling the volcanic blocks, ENVIRONMENTAL AND HISTORICAL FACTORS. 79 formed by the disruptive effects of the flow upon the crust, but the assistance of slope and gravity withdrawn, the material is immediately deposited. I do not think that 50 per cent of the material thus dropped has since been removed, except on the slope immediately facing the Santa Cruz River. In volume this wash amounts to less than one-fiftieth of the material of the hill. It will be seen, therefore, that erosion has scarcely touched the hill since it assumed its present form. ‘This recent caliche-cemented formation is called later wash to distinguish it from the wash formation underlying the tuff. In places it is thoroughly cemented with caliche, developed by the leaching of the porous amyg- daloidal surface of the lava flows. The pore spaces of the lava were originally filled with calcium carbonate and sulphate, which can still be found in freshly broken rock. The cement migrates down slope, spread- ing out in places and cementing the material of the Tucson Mountain slope, which is otherwise free from caliche. The Tumamoc wash just described extends out in a thin sheet over- lapping the Tucson Mountain wash. ‘The latter is not indicated on the map, but covers the andesite everywhere except in spots south and west of Tumamoc Hill. It is a subaerial wash deposited under torrential conditions. It is excellently stratified. Its material varies from the finest sand to bowlders 6 feet in diameter. The fine sand often forms a matrix in which the bowlders are embedded. Wind erosion is now rather more active than deposition, and in some spots some imperfect examples of desert pavement are developing. The wind is also exposing by erosion some of the coarse material formerly deposited in the temporary stream- channels. I have named these arroyo-trains,’ and the former course of the stream can be imperfectly traced by the heaps of this material at the surface. There is no direct evidence to determine the time in which the events just described took place, but the indirect evidence, such as the recency of the last faulting, the freshness of the basalt, and the increased length of time that has been allotted to the Pleistocene by recent studies suggests, as already stated, that the basaltic extrusions took place in the Pleistocene, and the andesite and rhyolite were erupted during Tertiary times. PETROGRAPHY. The rocks of Tumamoc Hill fall naturally into five types or classes, which are recognized in the following petrographical descriptions. OLIVINE BASALT. This is an exceedingly fine-grained, compact rock in which none of the mineralogical constituents can be identified without the microscope. When fresh it is black or very dark gray, sometimes quite free from cavi- 1Journal of the proceedings of the Arizona Miners’ Association, 1905-1906, pp. 13-17. 80 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. ties, but often rather cellular and even scoriaceous in structure. In portions which have become altered these cavities have frequently been filled with agate, gypsum, or calcite, minerals resulting from the breaking down of the complex silicates. Due to the same reactions, perhaps aided by arid conditions, the black basalt has in places become irregu- larly covered with thin films of white calcareous material. Reddish modifications due to oxidation of ferrous silicates are not common, though the black mass frequently presents dark, reddish-brown surfaces as the result of superficial alteration, aided perhaps by a concentration of basic material on the surface. Under the microscope the following constituents may be recognized: Plagioclase feldspar, pyroxene, olivine, magnetite, an occasional needle of apatite, and rather light-brown isotropic material. The feldspar appears entirely in the form of lath-shaped crystals frequently arranged in flow- lines and crowded against the olivine crystals. They average about 0.2 mm. in length and a few hundredths of a millimeter in width. The olivine appears as isolated rounded grains rarely over 0.5 mm. in diam- eter. Only occasionally does it show its characteristic orthorhombic crystallization. Its most common decomposition product in this type of basalt is red ferritic material. This frequently permeates the whole crystal, but is also often found as a halo surrounding it. In the lavas underlying the rhyolitic tuff, this mode of alteration has extended to _ such an extent as to make the olivine, which is rather abundant here, quite conspicuous even to the naked eye. Pyroxene appears as exceed- ingly small grains occupying the spaces between the feldspar laths. It rarely has developed into crystals of sufficient size to show very charac- teristic features. Without polarized light it is sometimes impossible to distinguish it from interstitial glass. Magnetite is present as black, unaltered crystals scattered throughout the slide. PLAGIOCLASE BASALT. This type of basalt consists of a dense, dark-gray to black ground- mass, in which are scattered numerous and unusually large phenocrysts of plagioclase, with an occasional crystal of lustrous black pyroxene. The feldspar sometimes appears as faulted and brecciated crystals fre- quently reaching a length of 20r3cm. They are quite fresh and the albite twinning can often be observed without the microscope. Angular out- lines are the most common, but there are specimens in which the crystals have been resorbed by the magma yielding rounded forms. The pyroxene appears as isolated crystals, usually about 4 mm. in length and separated by intervals varying in different specimens from 2 to 5 cm. In thin sections the ground mass is found to be made up chiefly of feldspar crystals varying in size from microlitic growths in the denser varieties to individuals which can easily be seen by a hand lens in the ENVIRONMENTAL AND HISTORICAL FACTORS. 81 coarser types of groundmass; pyroxene seems to occupy a subordinate position. Accessories are magnetite, olivine, and apatite. The pheno- crysts of pyroxene are fresh, rather dark colored for this mineral, and slightly pleochroic. They show high extinction angle and the other well-known characteristics of augite. The feldspars are of a rather basic type of labradorite, as shown by the extinction angle on the albite twin- ning plane. They are filled with black inclusions of the groundmass, sometimes radially arranged. Faint zonal extinction has also been noted. Olivine, when present, presents the same characteristics as in the olivine basalt described above. It is not at all abundant and in some slides is absent. For this reason, perhaps, some investigators might prefer to classify this type as a basaltic pyroxene andesite. AMYGDALOIDAL BASALT. Most specimens of this rock are too badly altered to admit of very satisfactory study. Megascopically it is a non-porphyritic rock, only an occasional crystal of pyroxene being easily recognized in the fresher pieces. It varies from yellowish-gray to reddish-brown, colors without doubt due to alteration. It contains in places numerous rounded cavi- ties which have become more or less filled with siliceous matter in the form of banded agate, chalcedony, jasper, and smoky quartz. Fine geodes of brilliant quartz crystals have occasionally been observed. The cavities frequently have a shell of agate, the interior being either empty or filled with calcite and siderite. Microscopically the rock consists of a groundmass of andesitic texture containing conspicuous crystals of feldspar and pyroxene with very sub- ordinate olivine. In some specimens the feldspar and pyroxene are quite fresh, but the olivine and more or less of the groundmass seems always to have altered to yellowish decomposition products. A similar rock occurs in another portion of the field. It is rather finer grained, although quite variable in different portions of the same mass, dark brown in color and, like the type just described, has given rise to considerable secondary silica in the form of red jasper and agate. Some parts of the mass show quite conspicuous feldspar phenocrysts close together and evenly arranged. Other specimens show porphyritically only reddish and yellowish alteration products of the ferro-magnesian minerals. The main mass, however, is quite dense and of even texture. RHYOLITIC TUFF. This is a light-gray rock, originally consisting of volcanic ash, but now consolidated into a mass of uniform texture and of sufficient strength to be used extensively as a building material. It contains numerous inclu- sions, mostly in the form of pumiceous material but sometimes of darker, more basic fragments which have given rise to concentric rings of striking appearance. 82 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. Under the microscope the rock is found to consist of isotropic masses of glass and kaolinized matter, numerous quartz fragments, broken feld- spar crystals, and shreds of ferro-magnesian minerals. The chemical composition of this rock is shown by the following analysis: Silica (SiOg i: cee ees, rae Aealeraes auc 72550 Iron (Fe,O,) and Alumina (Al,O3)...... 13.95 Lime (CaQie teat “eG te. series cote ei: I.4I Magnesia (MgO)5..yr Be es nie se Alkalies (Na.O and KO) e203 +s oer - 1ie7% otalin 5. aa se Ni aiee oe 100.93 The large percentage of alkalies doubtless accounts for the ease with which this rock disintegrates in damp foundations and similar places. BIOTITE ANDESITE. This rock appears to be made up of a light-gray groundmass containing small and evenly distributed phenocrysts of triclinic feldspar and varying amounts of biotite. It has a rather pleasing mottled appearance and is much used as a building stone in foundations. The chief variations noted are with reference to the amount and kind of the ferro-magnesian constituent. This is predominantly biotite. In some localities, however, specimens have been found in which it consists wholly of hornblende. Intermediate varieties also occur. Phenocrysts of quartz occasionally come in, making transition types toward the rhyolites. These variations may be termed dacites. The groundmass shows very slight variation in texture in different portions of the mass, but sometimes exhibits green- ish and reddish tints. The polarization microscope shows the rock to be a rather acid type of andesite. Biotite is in small crystals and in most slides not very abundant. ‘The plagioclase, as proved by the extinction angles, are rather acid labradorites. The groundmass is made up mostly of feldspar in approximately equidimensional masses, giving an appearance somewhat resembling the well-known granophyric structure of the rhyolites. Quartz, however, in most slides, is not present in determinable quantities. = eee preter > & 4 ~ q ‘ " . - ‘\ oe i. 4S ANT) i HIZO A Ce Ate Bhajeed Ok Co kT Loney Net rybar Oey ee. ere eas oy | sae bent tement at hen GENT « ; q (Fo | | ‘= ; 7 .t { H ; a | | le ies : ne Be ee ed | i*) / } t hel \ i ie ' * hy | c% Wh “AN a Oh : ‘. \ \ | .) 4 ~ t 110 326 ieee. t iene The summer rains began on July 3, 1907, with a shower amounting to 0.08 cm. (0.03 in.). The first effective shower, however, occurred on July 7, at which time 1.52 cm. (0.60 in.) of rain fell. After this the rains were well distributed throughout the remainder of July and August. It is apparent from the table that, until February, the period of the soil observations was exceedingly dry, although of course not as dry as is the ustial spring and early summer. Before the beginning of the soil records, the last effective shower occurred on September 3, amounting to 0.53 cm. (0.21 in.), and on September 17 occurred a shower of 0.12 cc. (0.07 in.). The rain-gage is located only a few meters from the station for soil observations on the hill, and there is no question as to the applicability of its records to the soil data for that station. Owing to the local nature of many showers in this region, it is possible that the precipitation recorded ENVIRONMENTAL AND HISTORICAL FACTORS. Q] here is not exactly that of the other three stations, but the discrepancy can not be great. ‘This local character of the showers is most marked in the period of the summer rains, and is not so strikingly manifest in the winter season. In table 5 are presented the soil-moisture data, in terms of percentage calculated on the dry weight of the soil. In the last two columns of the table are the precipitation data for the short periods between observations. TABLE 5.—Soil Movsture and Precipitation, from October 3, 1907, to April 11, 1908. a Per cent of soil moisture, calculated on dry weight. a Precipita- : r . : tion since Date. Hill. Larrea slope., Wash. River plain. Fee ee ok vation, 15 cm./30 cm./10 cm. 20 cm.|15 cm. 30 cm./15 cm./30 cm. cm. in. TQO7, OCEss 1.707 C25 1 Post Noses Sas 3.6 3.5 O83 oe Seer ae oe (Cte PA ae Ol ita) Pairs Pi ede ROH) 3% FAM TSO Hi OAO40.04 Cita ee ewe Gis ee TOs e ae OR el LAR | O.62 OL20 ap ig rr toe Prost 3.4 187.7 PTAO Vy $662 1 0.04 | 0.25 Nove To8be er Orr gos: eG On le NAO} 8.5. lost 9.1 Ol dt 520.60 NOVig2 7 ei oa ue Pe 752 ie Ont 6.7 2.7 etOLd 9.7 0.46.) 0318 Decree: 18.7 | 17.6 FA 6.3 5.9 ART I TOS Paki, $0.00" O.00 Dect a2 pai 505 Only SOU WW 92 003-5 GAM O90 18O,001C 0.00 MB ee oe Seem ies) 8 be! eg Baler. 6:6.) 5.0 4.4 2. Fo TOA 23.7. O00 a 0.00 19008, [ale 2. 447. Ry Oe Ea 6.4] 5.8 FY Sepp 1L-O' | 7.04 O00 |) 0100 VARS Ror eer yeaa) 7k Sia i OT te ALO Aa 2 O55 2182857 10262 ete elie De Oap Ler 6.9. 9,6.7 O76) 5:5.) 1O:7 SO O.12. 10.05 Hepes rT)... TS.0 1145 ood | 8.2 Sea | A.2 |) 10:4 8.4) O00} 0,00 Pell Ser sa Oe Ori) DIRGIRES. GAN TAO terd-Oll26.07)/ 27.54 2278) 1.49 Bela? Gee ae ree Pee 1452 110.7.) 8-2 1 10.0 } 16.0 10.614)50,.24 Mares soa 27-2 NTs 9.6 | 10.9 9 he C2 °F 19.0 VEO. 0:38 Ors Mare foray 025i ueeorr 7.9 9.5 6.1 ATM, DAIO Ws T5248 O25 |) hO211 Mare 22 22 10.0) m1o.s 6.9 725 5.8 4:6 $17.0.) FOs1 || 0.07 0.38 Petit Leas ercnoey SG o3 PT LOly 5.8 | 6.8 5.1 Woe Fie. 34 26.3 | O10") 0104 April zi hitsoF3 8.1 SATS) He6 5.3 it. OUSTO.9- | T1264) O.001) 0°60 1For o to 10 em. depth. 3For o to 15 cm. depth. *For o to g cm. depth. 4For o to 20 cm. depth. ®10 cm.(4 in.)of snow fell on this date, and the record may below. The snow re- mained but a few hours. It is unfortunate that the soil observations could not be begun before the end of the summer rains, at which season the soils approached their maximum water-content. The series of data here given is, however, instructive in regard to the effectiveness of the precipitation in moisten- ing the soil, as well as in regard to the degree of water retention exhib- ited by the several soil-types. All of the data given in tables 4 and 5 are presented graphically on plates 28 to 31. In the curves of soil-moisture there presented, the abscissas represent time and the ordinates the percentage of soil-moisture. Each plate represents the conditions for one type of soil. The curve for the greater depth is, in each case, drawn as a full line, that for the lesser depth as a broken one. The numbers on the curves denote the 92 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. percentage (ordinates) and are taken directly from table 5. The pre- cipitation has also been plotted, in the form of a gradatory graph, the vertical lines denoting the amounts of precipitation occurring on the corresponding dates. The figures above the graph show the amount of precipitation recorded. Traces are denoted by a hachure above the graph, accompanied by the letter 7. The horizontal lines serve merely to guide the eye. Hachures and figures below the graph denote the dates on which soil-moisture determinations were made. This notation facilitates comparison of the precipitation graph with the curve of soil- moisture. To further facilitate this comparison, the precipitation graph is repeated with each curve of soil-moisture, it being assumed to be identical for the several stations. Vertical lines through the curves denote the position of every tenth day, beginning with October 1. In attempting to interpret these curves of soil-moisture it must be remembered that the samples for the different dates are not from exactly the same point in the soil, and that where local variations in the mois- ture-content occur these may lead to unexplainable irregularities in the curves. This consideration is especially important in the case of the hill soil, where the irregularities of the underlying rock-surface, as well as the presence of large rock-masses in the soil, cause marked variations in soil-moisture at any given time. Masses of rock which lie partly in the air and partly in the soil are effective in the control of the soil- moisture about them in two ways: they facilitate the downward pene- tration of rain-water along their surfaces, and they greatly hinder the loss of water which has once penetrated to soil which lies beneath them. This disturbing effect of local variations in soil-moisture is of less impor- tance when the question at issue is the average moisture-content of the soil for a period of several observations than when the fluctuations in soil-moisture are to be considered. But at best, the method here used is to be regarded as giving results which are only approximate; its prob- able error must be relatively very large, although we have at present no means of determining its magnitude. From the curves it is apparent that the moisture-content at the lesser depth varies from time to time much more markedly than does that at the greater depth. This of course is to be expected, for the surface soils are first to be affected by precipitation as well as by evaporation. The deeper samplings, however, are more valuable than the others in relat- ing soil-moisture to plant activity, for most plants of this region gain access to a depth of 30 cm. in a very short time after germination, and the soil-moisture at this depth is probably a fair measure of the water available for the general activity of most forms. The cacti are, in general, a marked exception to this statement, as are, indeed, many other forms provided with storage organs. All of the curves exhibit also the very important lagging of the effect of precipitation behind the march of the precipitation itself. Thus, it ENVIRONMENTAL AND HISTORICAL FACTORS. 93 may be a number of days after the occurrence of a heavy shower or series of showers, before any effect of these is felt at the depth of 30 cm. This consideration emphasizes the inadequacy of mere precipitation data in any attempt to determine the moisture conditions under which the plants of any region live. The lagging in the opposite direction is also well shown by the curves, and is of even greater importance to plant-life in the desert. Thus, a dry period of several weeks may ensue without the occurrence of any appreciable change in the moisture conditions of the deeper soil layers. In general, the heavier the soil, the more important is this principle, but other factors must be considered. In the case of the hiil soil, the water contained in the deeper portions is lost only through plant transpiration and direct evaporation at the upper surface, but in that of the soil of the river-plain water is lost from a depth of 30 cm. both by an upward and by a downward movement. The underlying rock of the hill prevents water-loss downward, while the dry underlying soil- mass of the flood-plain absorbs water with great avidity and thus acts not unlike a process of evaporation effective from below, as in the case of a suspended porous clay pot of soil. From very limited data’ on the relation of the activities of desert plants to soil-moisture, it appears that the minimum for the activity of forms not possessed of storage organs probably lies in the vicinity of 10 per cent as here calculated. Making such an assumption, it appears that the hill soil at a depth of 30 cm. was in good condition for plant activity throughout the period of observation, and that the soil of the river-plain at the same depth was not in as good condition. The con- ditions at a depth of 30 cm. in the wash and at a depth of 20 cm. on the Larrea slope can not be regarded as favorable to plant growth, although during February and early March considerable moisture might have been available here. The moisture conditions of the surface layers of the soil must be re- . garded as the prime factor in the determination of germination, since seeds seldom find their way to very great depths and are unable, in most instances at least, to germinate without a relatively great supply of oxygen. It appears from the curves that germination was probably possible in the surface layers of all the soils throughout February and early March. In order that most perennials may succeed in the desert, their seeds must be able to germinate in the surface soil when this is moist, and the seedlings must send their roots downward rapidly enough to reach the deeper soil layers before they are overtaken by the desicca- tion of the surface soil. A large proportion of the seeds which germinate in the vicinity of the Desert Laboratory meet an untimely end through failure to fulfil this condition. 1For some data on the minimum of soil-moisture with which plants can be active, see Publication No. 50, Carnegie Institution of Washington, pp. 66-67. PLATE 28. 3 an 20 30 10 2030 20 30 10 20 ete 20 i Feaius OCTOBER,I907} NOVEMBER herrerd: JANUARY,1908] FEBRUARY Hee APRIL 3 1418 26 Lis 23 13 13 eT eo 12 TT OCTOBER,1907+ NOVEMBER ipeseeee eee FEBRUARY ne agile CURVES oF Sori-MorsturE, Tumamoc Hu. PEATE, 29. . wack 3 ZOnSO (Os eZO eee lOREZO aso [O27 20 33:0 lO Zo 2030 10 ae 1907 eee | DECEMBER JJANUARY,1908] FEBRUARY eee APRIL - CURVES OF SOIL-MOISTURE, Larrea SLOPE. PEATE 30. 10 24:20 —s BHO 1207 30 lO ZOrs@ 20 30 OCTOBER,I907} NOVEMBER MARCH [OS ZO RS) LOMRZO SO 10) "20 10 DECEMBER |JJANUARY,1908] FEBRUARY APRIL 3 1418 26 i323 13 i3 23 {2 13 27 |I a ee eerie i OCTOBER,1907} NOVEMBER DECEMBER |JANUARY,1908] FEBRUARY MARCH APRIL CURVES OF SOIL-MOISTURE, WASH. PEATIESaa 20 30 10 20 30 1020030 AO pe20 ive OCTOBER,|!907 NOVEMBER DECEMBER MARCH APRIL ayr4 1B. 26 Rots Tala oe ie ee ee nan: STi he ON I SEN Ili 6 23 peels |OCTOBER,I907} NOVEMBER | DECEMBER |JANUARY,1908] FEBRUARY MARCH APRIL CURVES OF SOIL-MOISTURE, SANTA CRUZ PLAIN. 94 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. CLIMATIC CONDITIONS. The general climatic conditions which prevail in the region in which the Desert Laboratory is located are well known. They are, briefly stated, such as are necessarily characteristic of more or less elevated, semi-arid, continental areas in lower and middle latitudes. The annual precipitation is meager and irregular in amount, and this, with low rela- tive humidity, high rate of evaporation, wide diurnal range of tempera- ture, high winds, and intense insolation, presents a combination of trying conditions, to which, however, a large number of plant species have successfully adapted themselves. These conditions are, in general, characteristic of all the great desert regions of the globe, which, however, differ widely in important partic- ulars, the differences being reflected more or less distinctly in the habits and distribution of the plants inhabiting them. As an example, the distribution of rainfall in the desert region of the southwestern United States is essentially different from what it is in the Egyptian-Arabian deserts. In the latter the period of maximum rainfall and of greatest vegetative activity is in the winter, while in summer the vegetation is practically dormant, the time at which on the Laboratory domain the summer annuals are at the height of their vigorous growth. Such a state of affairs necessarily results in great differences, not only in the character of the summer vegetation, but also in periods of growth of perennials, and in structural and physiological relations. The studies of this subject at the Desert Laboratory by Cannon (1905) are highly sug- gestive and show the desirability of extended investigation. The lack in botanical literature of sufficiently detailed observation and experiment regarding local climatic conditions in their relation to the growth and distribution of plants suggests that, without attempting a discussion of the broad subject of desert climates, it will be desirable in this place to call attention to a limited number of recent records and studies looking toward more exact knowledge of local conditions and their influence ou the distribution of plants. RECORDS OF RAINFALL. Records of rainfall show that in this region the amount of precipita- tion is extremely variable from year to year in the same place, and that it often differs very considerably in places not widely remote from each other. In table 6 are given the records as taken at the Arizona Agri- cultural Experiment Station and at the Desert Laboratory, 3 miles distant and at approximately 200 feet greater altitude, for the period March, 1906, to May, 1907, inclusive. They show a fairly close corre- spondence for most storms, but it is also seen that summer rains espe- cially, even at this short distance, are often extremely irregular and unlike in amount of precipitation at the two points. As an example, ENVIRONMENTAL AND HISTORICAL FACTORS. 95 the records for July 14-15, 1906, give an aggregate rainfall of 1.16 inches at the Desert Laboratory and 0.49 inch at the Experiment Station, while for August 10-11, 1906, the amounts recorded are a trace at the Laboratory and 0.88 inch at the Experiment Station. Enough is known of the habits of the plants of the Laboratory domain to establish the fact that such differences of precipitation profoundly affect development, and in critical years may be associated with conspicuous failure on the part of many species of annuals to appear in their customary places. TABLE 6.—Records of Rainfall at Desert Laboratory and University of Arizona, March, 1906, to May, 1907, inclusive. Date. Lab. | Univ. Date. Lab. | Univ. Date. Labs 4 Untv; 1906. Inches. | Inches. 1906. Inches. | Inches. 1907. Inches. | Inches. Mis ratte Os OL 75 MPAs ter Uo tei ec Tat MA BSiO .0O2%) fa 202 eo | Cee “E3 Ince O-O0Le | O00 Cieiae coats 1% Doe Ren. fie Fis datire ey: . 42 ee fo See Ae Pe. Oi. 0.03 Por) O47 0.59 5 RA Oe ee O.O1 ZOnn O.. 23 0.26 TO Oe sO) HLOs2s ES fa LO ex ZT et O.0225) 0.045 COM Oar | Orse 16-2) 0.02 }.0.20 P 8 0Ces engage. ae ; cee cae O.OI Cte) Sater ah: mote O- 1-0 .01 |. O-30 ig ii. aera LO Meee eat o.25 PIANO 34 0.14 BEEN, OOF Ws sts 19.4) O35 Oui! May 23) 4) @.0183|"1. One i oe 2OcLNe Lo 0.01 ty eter 0.02 Brea O.02 1G, OF 2004) On 8F) | 0.20 tO. O83 50 tr screae: SeEptgn0 yor err fy. Bir ies. Jee O.O1 Gen peace Pe PA 210) | Osa4 HebuitG. cr 2) 0.035 LO errr ee 0.04 27 O18 |. 0200 Pore ie O.OI? TS, LOMtIVe:, 16 Octo, 01605 141. 2 (ewe SE8e 0.04 he et eee ee nee NOVA. 1smi.00055 | 0.07 25d 0.08 4. 0.025 oe. el, aye a aso eee ‘ FW ha cea im! 1451 GOO WO 440 LOM. OrAUS) | O52 Mag. 95: 210.256 1.0240 Ih ach 0.27. -|.0,09 2A 2) O219e OnL5 22 el OSLO) On 1G TO eee 0.04 SSE DU haste: 218% aad Meds a ec Bia) bees, ce O.O1 Decoy 2 io.65a) |:o390 ie tala) Ls) ey teed EA eee ‘ie Beles OO tee aT 5 CA ANE 0.015 2) nt a Velho Mi ees elt DB ly eee es ee i da eae Te 260150702 1.06 Deir Oper Mata Lt oy perk he ae eee ae POROOS | oan AOpen ST 1 Oe 20 este ti Ake ‘be i: A pS al AORN Pana 0.03 AS hosed le se ws At AT eye ihe 1907. Mayon oto jee Aum erie OsrTeo to. 3r SY ioe ie aah Bey et Pho ad cesar 0.06 les Wee ; Zee O-OF Outs 2Ot| Orton | Ort Toa) als 0.26 Che SOLOL= WOe1G 5% Sie ea 0.62 ide aed 0.08 1Snow. The records of table 6 are also of importance in connection with the measurements of the sahuaro, which prove its capacity for the prompt absorption and storage of water after even very light rains. ‘There can be no doubt that by this means the giant cactus is placed at a distinct advantage throughout its range and in its association with more deeply rooted plants. More definite, as regards the intimate relation existing between dis- tribution of precipitation and of vegetation at various points in southern Arizona, is a recent paper by Prof. J. J. Thornber to which I am per- mitted to refer in advance of its publication elsewhere. A comparison 96 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. of winter and summer rainfall at 53 different places, from such records as are accessible, shows that, in general, at points east and south of Tucson, the aggregate summer rains are considerably in excess of the winter rains, while to the west of that place the reverse is true (table 7). This difference is due to the fact that to the eastward and southeast the Gulf storms become more and more a controlling element, while on approach- ing the Pacific the conditions become dominant which, in southern California, limit the rainfall to the winter months. This difference is such as to very noticeably affect vegetation. Particularly is this true of range grasses which by reason of preponderance of summer rains to the east and south find there more favorable conditions for development than to the westward, a matter of much economical importance to stockmen. Table 7, compiled by Professor Thornber, shows how few are the excep- tions to the general rule as stated, and that it holds true notwithstanding rather wide differences of altitude, which necessarily affect the amount of rainfall. TEMPERATURE RECORDS. The account that has been given (pp. 44-47) of soil and air tempera- tures at the gulch near the Desert Laboratory points to differences of temperature as the primary factor to which the remarkable differences of the plant covering on the two sides of the gulch are due. In this case it has been possible to establish a causal relation between observed facts of distribution and a single physical factor, which though operating in part indirectly is none the less the fundamental cause of the phenomena in question. The rather voluminous readings from which the results are deduced are given in tables 8 to Io, in sufficient number to indicate the nature of the data. Maximum and minimum readings are for either one or two days, except in a single instance in which a period of three days was covered. In field studies of this nature nothing is more important than to bear in mind the futility of attempting to account for facts of distribution without due consideration of all the factors involved. To emphasize the influence of a given factor is one thing; to ignore those acting in conjunction with it is quite another. As pointed out by Dr. Cannon (p. 60 et seq.), the superficially placed root-system of Cereus giganteus subjects it to conditions of soil temperature widely different from those affecting Parkinsoma nucrophylla, with which, however, it is almost constantly associated, and innumerable similar cases emphasize the fundamental fact that plant associations, while often conspicuously related, as a whole, to a single factor, are composed of species often of widely different habits, responding in different ways and degrees not to one, but to all the factors of their environment. Under such circumstances any practical method of simplifying the problem of measuring and correlating physical factors with choice of habitat is particularly welcome. Some progress has been made in developing such a method, as will be seen on pages 99-100. ENVIRONMENTAL AND HISTORICAL FACTORS. TABLE 7.—Drstribution of Rainfall. STATIONS WEST OF THE MERIDIAN OF THE DESERT LABORATORY. YS oF Station. Pe ee an cain cipitation ’ Feet. Inches. Inches. Inches. PIGCeNCGMEe ga taa ft: cathe. 13 1,700 2.81 Sak 5 9.78 Casal S teres ec We. wh 14 1,395 ronwae 2.07 5.29 Manica pawt tts aes 2 3 18 We Ayes 1.97 a1G 5.50 iMdatalcet s(t ea Sl ree a geen 15 1,100 2236 3. OF 7.08 NGkenere Tuer. cao. es 10 2,086 3.46 5.89 9.85 ECL Nste mente fe iltea 9 RoR 19 150 0.65 2.06 3605 0 Te PA a oe a 13 4,501 a Pen ee 8.61 17 2 PECSCOLLER TS Fs ous oe oe 27 5,304 6.89 8.34 16.25 Fort McDowell....... 23 1,800 2.62 ae: 10.45 BAS a Oe i Sk One. Serna 5 1,865 oly | 4.87 10.99 EIEIO EV ALLCVe ia aa cet ee wee arn e § 6.32 12.85 DIALS Parley c Campa. ats Ad Mittin tnt Stn i 9.46 Gye ING@wy GN tvege 4 ce en Ste Qe ka aes ZL 1 meaty TO. EY PUCAWHETE Ye. te ee a oe el teres cr ee 17.20 26.59 WialnutiGroveds.s oh de: oa. Be eee ee eles 8.60 het Wood Canyon 9.0 2.1. os =. So a ee 9.50 ee ew Pe her ay Horaibouaye. scoke. sate hh ole wee 600 0.95 3.90 5.32 Wiles Gali in ery oo elede oe 9 6,870 Ton 12.08 25561 SERS? LAV RES! orbs. fe, yy ee en) Eee et 0.74 1.91 3.09 La Me cpr rc eat eee Wc’ ons Ce) ee knee Ax73 G233 12.19 Stlagmeliiens tte aa cules al 5 as 1295 3.68 6.15 INeeurak Bridge. 4. Gaus a2) | a ee 5-94 kino 19.49 Peoria ties.) ee tee Sk Rear rae se wk 2.79 4.68 8752 PeNIe a sg oe eee ee 5 1,000 Bert 28 8.63 DES are Sc OMe dete Ek A eh RN tee 8 60 17.07 MeQOdritit,.. ne dehec ck coe. «2 een 1 eed, ao 7 6.54 | Ore Ye, Ne Ras leiy 2.8! eu geee Mee thee MPR eee 8 5,057 3.68 a5a2 8.46 A SGOHEY, Sp TUN fer ee 28 ale ee as: 8,000 8.93 E704) 30.07 Canip DalrCreck: (sa... oF ey ae 6.87 6.52 {A422 STATIONS EAST OF THE MERIDIAN OF THE DESERT LABORATORY. Fort Lowell San Carlos ‘Tucson Benson Pantano Baipire hauch: jee. oa dee ys San Simon Weenie mame Se ee ee Fort Huachuca... . Fort Grant Pcie OWI. ee es ean ote Denhance... 26 cane Cy ety eee et Pe ied eal eae 16) een ine gien sid’ omaha, 5: SP vat efaist ope) (G0 Wene) er se) he, a: iaui@’ i ai Ae a) a) Ke oe AO Sacer ae, 6 |e: ele) yapetel is! vel" [oj /a'e) (6), ost. Ske tet se. aiisy 6. el 8t a) 6. 0 Calabasas Camp: Crittenden: — oh. estan. - Chiricahua Mountains...... EW aS OOM a taps nic tiny Areas Dragoon Summit... eee Lochiel Walout Ranch: is. evowa ees. Piatt DAMICCe 5 so ccss ok «er es Fort Buchanan CRON a eee sb ag at > bie) ate w, Be, vB (6) 6) 8) fa! lis os we Roe. eo Lela lence BAWOMNWHWANUYW 2,539 2,400 2,371 <3) a) te) © (By ie) efile 6,6. 0) et de fast CC CRMC) Te] ef Sh ay 0! (ein efwiel te Sm 8 6, 0) (we) © Sy <6 6 a) ie), ew) © CU OCU Kom 6.64 4.93 12 42 4.93 (ORS. 1 ee. 5.26 Aw24 10.70 4 60 Pl 8 7228 6.03 Ar2AT 12.40 9.10 405)" | L522 2.41 1.65 4.49 5-46 2.64 10.21 9-45 4.84 55233 7-39 5-39 12.82 7-03 6.33 15.33 7.03 [ee 14.19 Seek Ew 11.99 9.51 4.76 15.38 7-27 Ol 12.34 11.56 4.40 16.51 52727 Bast 22.2 6.46 4.90 Lover 6.41 2 AA LILI ri 02 6.40 19.26 itt 5.11 13491 fie ee) 22 10.83 13.44 6.02 21-55 5-40 A108 tH. 61 98 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. TABLE 8—Maximum and Minimum Soil Thermometers (Bulb at Depth of 1 Foot below Surface). 1906. 1907. Station I. Station IT. Station I. Station IT. Date. Date. Min. | Max. | Min. | Max. Min. | Max. | Min. | Max. rice a eet re we hy, dak ek re Decswio..# 54 56 49.5| 50 Mavis. oo 75 80 5 fe 74 Deco... 54 56 49 49 May 05.5.5) 73 #89! 69 70 Dec a2. a 54 57 49 49 May 17.. 75 80 69 73 Deca. 55 58.5! 49.5] 50 May 2022-2) 775 82 73 a5; TABLE 9.—Minimum and Maximum Soil Thermometers (Bulb at Depth of 1 Inch below Surface). Station I. Station IT. Station I. Station II. Date. Date. Min. | Max. | Min. | Max. Min. | Max. /} Min. | Max. 1907. sy aie foal abe rg Sey TN oe 1907. OF fod 2 Pic ae Fe. tna Fae Marnagoe.: 63 88.5} 60 67 Aprilia. 65 98 62 42 Mar. 25 22).11N50 go 51 60 May eri: 62 ros 96 62 74 Mat.5205 52. |ees0 80 45 58 May-s S32. 65 97 64 75 April 12.6 a7 103 64.5) 71 May 710... 4 G4 97-5| 64 75 Apri sis! eat 103.54 605 75 TABLE 10.—Air Temperatures at 1 to 2 Inches above the Surface. Station I. Station IT. Station I. Station IT. Date. Date. Sun. |Shade.) Sun. |Shade. Sun. |Shade.| Sun. |Shade. 1907. re vise. er, Cre. 1907. oak oF; wie ta ae yale e267. 85 65 64 57 April*ro.. 4) 120 98 120 80 Janae 89 64 70 56 Aprile, . jerae 96 122 85 Feb, 2 95 65 7% 57 ADVISE oe at rt 88 II4 80 Heb. Ge. 98 vie 83 65 April oo. >. str 85 103 76 Rebelo ee 106 76 87 66 AprilieG. 2/1108 80° 1) 114 ai. Feb; 13 94 71 78 62 May r.5. 5) Ior a IOI 76 Feb. 25.. 96 7a 82 64 May? fase. ai a7 90 | 120 80 Matin Sat a: 93 63 87 52 May »6.454) 98 a, 110 71 Mar. 9g.. 106 69 86 56 May? © 32.2 J 150 80 rr 768 | Mar, I1.. 104 76 96 66 May Io. 114 83 A 78 Matar se. 153 95, g2 68 May tr37. 97 70 100 68 Mar. 20 08 105 75 82 65 May 15.. 114 86 124 82 April’ °3..: 12 90 119 83 May 20.. 116 gI 126 go ENVIRONMENTAL AND HISTORICAL FACTORS. 99 MEASUREMENTS OF EVAPORATION. Recent work by Livingston (1907, 1908) at the Desert Laboratory on evaporation and plant development and habitats, in connection with observations at stations representing widely different climatic conditions in different parts of the United States, indicate the great importance of this line of research. It is shown by Dr. Livingston in the papers referred to that the evapo- rating power of the air depends upon three factors—humidity, tempera- ture, and wind velocity—and that measurement of evaporation, which is simpler than the measurement of any one of these, gives the directly controlling factor in water-loss from plants. For a given soil-moisture content, there is a maximum rate of water-supply to any plant through root-absorption, and when the evaporating power of the air is great enough to cause the rate of loss to surpass that of supply, the plant wilts and suffers injury, and death even may ensue. If the rate of transpiration approaches or equals that of supply, little or no growth can take place. It appears, therefore, that evaporation must be considered as capable of affecting the plant directly, as well as through its indirect effect on soil-moisture conditions. In arid regions it seems that this effect is par- ticularly marked, and that here evaporation actually inhibits the growth of many plants, even though the soil-moisture content may be rather high. The conclusion necessarily follows that evaporation may exercise a determining influence on the distribution of plants in different habitats, even in relatively close proximity. The methods of experimentation, with full descriptions of the apparatus employed, are given by the author in the papers referred to, and it is only necessary here to refer briefly to the results, which indicate, as already stated, that in any habitat, but especially in arid regions, the evaporating power of the air is one of the most important among the conditions which determine local distribution, and that the measure of evaporation for a given locality also includes some evidence in regard to soil-moisture, which is of even greater importance to plant life than the atmospheric conditions. Turning for the moment from desert conditions, some comparisons of rate of evaporation at certain mountain stations in the neighborhood of Tucson and at points in the eastern United States are of great interest. The highest instrument on the Santa Catalina Mountains was set up at an altitude of 8,000 feet, and showed, for the latter half of May, 1907, a weekly rate of evaporation equal to 133 c.c. During the same period the instruments at Orono, Maine, and Burlington, Vermont, indicated a weekly rate of evaporation of 123 c.c., and 112 c.c., respectively. Such correspondence of rate is the more striking in view of the fact stated by Livingston (1908, p. 8) that ‘‘the vegetation about the highest instrument in the Santa Catalina Mountains possesses the same ecological characters 100 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. as that in the vicinity of Orono and Burlington, the higher levels of the Santa Catalinas being occupied by pine, spruce, maple, alder, elder, cornel, brake, columbine, violet, etc. F‘urthermore, plants in Maine and Ver- mont were in about the same condition as those at our upper station at this time of year.’’ Results of this kind suggest the value and probable extensive use of this method of measuring evaporation as a means of determining ecological equivalency, whether at near or remote points, a matter of fundamental importance, which as yet has received but little attention. Recent studies of Transeau (1905, 1908) on the relation of plant so- cieties to evaporation further emphasize the value of these methods of investigation and the importance of rate of evaporation in determining the distribution and succession of plants. Earlier papers by the same author go to show that a close relation may be traced between the dis- tribution of forests in the United States and the combined figures for rainfall and evaporation. With no attempt to minimize the edaphic, geographic, and historical factors, it is made evident that climatic differ- ences which may be expressed in ratios obtained by dividing the mean annual rainfall by the depth of evaporation at the same station, correspond in a very striking way with the relative position of forest, prairie, and arid plains. ANIMALS OF THE LABORATORY DOMAIN. No comprehensive study of the animals of the Laboratory domain in their relations to its plant life has yet been undertaken, though it can not be doubted that this would lead to important results. As has been shown in the section on means and agencies of distribution, the inter- relations of desert plants and animals are particularly close and varied, largely advantageous to both, though often quite the reverse. Changes of the flora must react, sometimes directly and manifestly, at other times indirectly and obscurely, upon the fauna, and vice versa, but the history of these relations has never been followed far in this region. A few zoologists who have taken up the study of certain groups of ani- mals from an ecological standpoint have made valuable contributions. Of these may be specially mentioned the recent studies of reptiles and am- phibians by Ruthven (1907). His work, too extended to be reported here in detail, includes a discriminating account of the habitat relations of the various reptiles and amphibians collected in the vicinity of Tucson. The habitats described correspond essentially with those defined in the present work, and it is significant that notwithstanding the wide range of certain species, as for example some of the bull-snakes, which are found from the flood-plain of the Santa Cruz River to the pifion zone of the mountains, there is a well-established preference, as a rule, for the habitat of some special association of plants. Thus the large lizard Sceloporus magister is said to be “common on the greasewood plains’’ and also to occur, with the ocotillo and sahuaro, at the foot of the Santa Cata- lina and Tucson Mountains, though much less common in these latter places; so that its principal habitat in this region is preeminently that of the creosote-bush association of plants. Similar notes regarding a large percentage of other animals taken in the vicinity of both Tucson and Alamogordo indicate that many of them at least exhibit a like habitat preference. ‘This is expressed by the author in the general statement that each set of environmental conditions which is marked out by a distinct plant association has a definite reptile fauna. The summary with which the paper closes is of much interest, and some of the general statements apply equally to both plant and animal forms; it must be said, however, that our present knowledge of the distribution of plants on the arid plains by no means warrants, for these, the application of some ef the theoretical conclusions of the paper cited. The hypothesis “that the reptiles of the arid plains have had their origin in this general region (Mexican plateau and proplateau), and that the forms of the pifion-cedar and pine-spruce associations have been derived from them”’ would give, especially as regards the second proposition, a very inadequate, not to 101 102 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. say erroneous impression, .1f applied to plant species. Furthermore, it can not be doubted that “the arid-plains forms tend to become the climax type’’ in the southwestern United States, but in this region, where such tendencies are liable at any moment to be corrected by the process of volcanic uplift, the future disposition of plant and animal associations and habitats can only be tentatively suggested. Several recent papers of Professor Wheeler (1907) should also be noticed, although they are quite too voluminous to permit more than the barest reference. In the course of his investigation of the fungus- growing ants of North America, it was found that in the wash near the Desert Laboratory a catclaw (Acacia greggit) in the neighborhood of the nests of Atta versicolor had been completely defoliated by colonies of these ants, which suggests on their part a relation to vegetation which may often be prejudicial to the latter, however efficient they may be as agents of seed dissemination. Another paper of this writer (Wheeler, 1907), though not directly discussing questions of plant distribution, is of special interest in its bearing on the origin of habits and adapta- tions, fundamental as they are in relation to distributional problems, as studied in a group of animals which is described as having become the dominant invertebrates of tropical America. Experiments conducted by Prof. W. L. Tower involving the mutual relations of certain plants and animals are now in progress in the vicin- ity of the Desert Laboratory, where colonies of Leptinotarsa have been established. No report of this can yet be made, but the previous work of this investigator, which has already been referred to, is of special interest and value as embodying, with much else, a study of a single genus of animals with reference to the local distribution and wider migra- tions of its species, serving thus to indicate a rational method of pro- cedure in following out the geographical history of desert plants. (See Tower, 1906.) Reference should also be made to the well-known papers of Adams (1902) and especially to his views regarding the probable existence of a characteristic and varied fauna and flora in the Southwest during the Ice Age. These, in general, are in accordance with the results indicated in the special contributions presented with this paper and referred to in the closing discussion. CHAPTER IV. VEGETATION GROUPS OF THE DESERT LABORATORY DOMAIN. ' The following list includes as nearly-as possible the plants growing on Tumamoc Hill, the fenced area of the mesa-like mountain-slopes lying to the west, and the Santa Cruz flood-plain between Tumamoc Hill and the Santa Cruz River on the east, together with the hydrophytic species growing in the Santa Cruz River and adjacent irrigation ditches. For convenience the areas noted above have been designated as follows: (I) Tumamoc Hill; (11) Mesa-like mountain-slopes; (III) Santa Cruz flood-plain; (IV) Santa Cruz River and irrigation ditches. The species of each of the above areas have been arranged alphabeti- cally under the following vegetation forms: (1) trees; (2) shrubs; (3) woody climbers; (4) dwarf shrubs; (5) half-shrubs; (6) perennial herbs; (7) biennial herbs; (8) annual herbs including (a) long-lived annuals; (b) winter annuals; (c) summer annuals. ‘The occurrence of a species in any quantity in an area other than the one of which it is characteristic is shown by a Roman numeral indicating the area over which its secondary distribution obtains. Besides the four groups of plants corresponding to the four areas above noted it is thought desirable to include a fifth com- posed of miscellaneous introduced species which have become established here by virtue of certain inherent qualities or characters. ‘These exotic species are limited almost wholly to area III, though a fewoccur in I and II In questions of nomenclature the recommendations of the Vienna Congress of 1905 have been followed as closely as possible. For con- venience synonyms are given as they stand in the second edition of Heller’s Catalogue of North American Plants. The writer gratefully acknowledges assistance from numerous sources in the preparation of this list of plants. Most of the Graminee have been passed upon at one time or another during the last few years by Professors Scribner, Hitchcock, and others of the Bureau of Plant Indus- try, U. S. Department of Agriculture. Dr. J. N. Rose, of the Smithsonian Institution, who during his trip through the Southwest last spring spent some time in studying the Cactacez in the field, has determined several species which had hitherto remained unnamed. Prof. P. Beveredge Kennedy, of the University of Nevada, has kindly verified the species of Atriplex; while Mr. Paul C. Standley, of the New Mexico College of 1Prepared by request and Contributed by J. J. Thornber, A. M., Professor of Botany in the Arizona Experiment Station. 103 104 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. Agriculture and Mechanic Arts, has worked over the various members of the family Allionacea, on which group he is preparing a publication. Prof. H. M. Hall, of the University of California, has verified the names of miscellaneous plants from time to time from this locality. TABLE 11.— Showing the Various Spectes from Standpoints of Habitat and Vegetation Form. igi: II. Tis erie | Santa | se Santas) (Cruz. Intros Vegetation forms. _ Tuma- nome roe Rivér | duced” Total. moc Hill. AGE. flood- | and irri-| species. plain gation | SlOpee: 4 ditches. | | ele af ‘Thees sign be. eae eee | 2 2 UHL , SASS E ae Ate eke 15 SHCODS chee 8 eee ee ee | 16 IO LO es sree 3 39 W Oody twiners-..-) ee RDA per ae Ml Reet eto a? by 3 5 Jowartshrabs (io). | ra ES SEO es ere BR ey ee, ed 17 Hali-chrubs< reetage | On al Tek Wa ere I 2 \iPerennialtherbers., -aakoeoe 4 1,4 . ® ny A! ae eee nan lapse Opie tapes 7 t CHAPTER VII. SUMMARY. The work thus far completed, with the most important results, may be summarized as follows: (1) Within the limits of the Desert Laboratory domain and that part of the Santa Cruz Valley immediately adjacent, chosen as a representa- tive area for the study of desert plants in southern Arizona, 12 plant associations have been recognized and defined. These fall naturally into A groups corresponding with the main topographical features of the area under observation. ‘The local distribution of certain species of these associations has been carefully mapped with special reference to topo- graphical and soil relations, by this means confirming conclusions based on previous observation. (2) Observations within this limited area, supplemented by compara- tive studies in the Gila Valley and elsewhere, have led to the conclusion that soil properties and aspect are of paramount importance in deter- mining the local distribution of desert plants. With regard to the former, evidence has been gained that soil-water exercises a controlling influence, but that, with certain species at least, aeration and percentage of alkali salts are also efficient factors. (3) These conclusions have been confirmed by investigations of the soils of the Laboratory domain conducted by Dr. B. E. Livingston. The correspondence between per cent of soil-moisture and the distribution of both the plant associations and their constituent species is especially striking and convincing. (4) The importance of aspect in determining distribution on closely adjacent areas has been shown by many different observations, but especially by floristic comparison of opposite sides of the gulch near the Laboratory, where, on equivalent areas, 2.5 times as many species are found on the northerly as on the southerly exposure, and the difference in number of individual plants is still more striking. Analysis of aspect preference, in connection with its observation at different altitudes and continued records of temperature, leads to the conclusion that it is correlated first of all with range of temperature, though other factors, in certain cases at least, are involved. It appears clear that whatever else is involved the lower temperatures of winter on northern exposures at this place have interfered with their occupa- tion, to any considerable extent, by the sahuaro and Fncelza, while the extreme heat of southern exposures in summer has, at this altitude, prevented their occupation by various species, of which Lippra wraghtir is a notable example. The behavior of this plant at different altitudes 139 140 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. affords confirmatory evidence of the fundamental importance of tem- perature in the determination of aspect preference. é (5) Light has been thrown on the causal relations involved in habitat preferences by the study of inherited habits and structures of certain species. Some at least, and possibly a large proportion of the plants which have become established within the Laboratory domain, have entered it with correspondingly great differences of habit and power of accommodation to conditions which exist here. These differences are con- spicuously manifested in choice of habitat, especially as regards aspect and soil preferences, and also in their relation to other members of the same association. fEncelia is a genus of subtropical species, chiefly, and its representative on the Laboratory domain finds most congenial con- ditions on southerly exposures, just as Delphinium and other plants of cooler and moister regions find their places here on northern slopes. The characteristics of the root-system of Cereus giganteus which have been worked out by Dr. W. A. Cannon, taken in connection with its arrange- ments for water storage and high temperature requirement, satisfactorily explain its limitations in both local and general distribution, pp. 59-66. Peculiarities of structure and habits, correlated with water-supply on the one hand and temperature relations on the other, are exhibited by a large percentage of plants of the Laboratory domain. These structures and habits have determined, and are still determining, the continued existence of the various species in places where they are now growing. (6) It is none the less certain, however, that there are here examples of plants in which the capacity for individual adjustment to changes of condition is a highly potent factor in the determination of local dis- tribution. The creosote-bush presents a case in point. It can not be doubted that to its extraordinary power of adjustment this plant owes its capacity of retaining its place on the long slopes, where, under the extremely adverse conditions there prevailing, it forms a conspicuous belt of vegetation, from which other perennial plants are largely absent, and at the same time flourishes in the low ground of the wash and grows luxuriantly along irrigating ditches, where it has an abundant water- supply. The same plant, together with the ocotillo and some others, shows its capacity for individual adjustment in its perfect indifference to change of aspect, to which so many species of Tumamoc Hill are exceedingly sensitive. The ready growth of Suweda moquini in the worst salt-spots, and at the same time along irrigating ditches conveying fresh water, is still another illustration. Fundamentally these cases of adjustment are the same as those of adaptation just cited. In the one case, as in the other, inherited peculi- arities determine the limits of choice. It is true, however, that a species without prominent structural adaptations may, by its inherited capacity of ready physiological adjustment, be a far more successful element of SUMMARY. 141 desert vegetation than some more highly specialized forms. ‘The remark- able adaptations of the sahuaro are in strong contrast with the simple structures of the creosote-bush, but the latter ranges far more widely than the former, and stubbornly endures vicissitudes to which the sahuaro, even in the areas of its best development, inevitably succumbs. (7) It has become evident that the relations of desert plants to each other are not less important than their relations to their physical envi- ronment. The commonly received view that desert plants are engaged in a struggle with their environment, and not with each other, requires material modification in view of what has been observed to take place on Tumamoc Hill, where vigorous competition between different species and different individuals of the same species goes on from year to year. There is also a mutual accommodation, in certain cases, by which plants with root-systems reaching different levels are enabled to live advan- tageously in close proximity. It is plain that no general statement of the relation of desert plants to each other can be formulated at present. Each species requires investigation in its relation to its immediate asso- ciates, and when, as must happen, both competition and accommodation are involved the complicated nature of the problem is manifest. (8) Passing to matters pertaining to general movements of desert plants, it may be said that the agencies and structures operative in the dissem- ination of seeds and propagative bodies of plants on the domain of the Desert Laboratory present no special features, so far recognizable, and no unusual interpretation of their action is necessary to account for the presence of the species found here. The plants which have been brought by various efficient agencies are of widely different geographical origin. ‘The analysis of the flora, par- ticularly as regards the genera, indicates for some of them northern Mexico as their center of dispersal, for others tropical or subtropical America, for another contingent the northwestern United States, and for another the high northern regions of either hemisphere, while still others, including miscellaneous introduced species, have come from vari- ous parts of the world by the most diverse routes, some of which have been satisfactorily traced. (9) It is noteworthy that between 400 and 500 species of plants, of such diverse geographical origins, should have been able to establish themselves within the narrow limits of the Tumamoc Hills and the adja- cent valley and accommodate themselves to the somewhat trying cli- - matic conditions prevailing here, since the effectiveness of general climatic factors in limiting the range of species is well known. Important in this connection are the observations of Professor Thornber on the relation between the annual distribution of rainfall and vegetation in southern Arizona, according to which it appears that grasses are favored by the preponderance of summer rainfall to the east and south of Tucson, in contrast to preponderating winter rainfall to the west. 142 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. The experimental work of Dr. Livingston on evaporation has gone far to provide an efficient means of testing the ecological equivalence of habitats, and this work goes to show the value and practicality of maps of distribution based on the principle of such equivalency, which would serve, as nothing else could, as a rational basis for various horticultural undertakings, that at present are in an almost wholly empirical stage. (10) The general continuity of geological history since the Tertiary indicates a relatively long period within which plants of the Laboratory domain have one by one, or at any rate by no mass movements, become established in their places. There is reason to believe that throughout this period the processes now going on before our eyes have been in progress. ‘The present flora, therefore, may be assumed to be merely the final stage, thus far, of just such a series of events as are now observ- able. Invasions have taken place, competition has ensued, certain spe- cies have become established as prominent constituents of the various associations, while others have died out or taken subordinate places. Species now growing side by side have reached Tumamoc Hill from widely separated regions and at intervals of possibly thousands of years apart. The small area within its limits has received representatives of genera that have shared in the great migrations south and north along the Cordilleras, but through the time that has elasped since these greater movements it has also received, by entirely ordinary means, the plants that have come and are still coming to it. The general history is not essentially affected by the fact that portions of Tumamoc Hill are of quite recent origin. These parts give evidence of having received their ~ flora in the main from the immediate neighborhood, although certain genera have come from points at some little distance, without settling in the less favorable intervening territory. If, then, as the evidence seems to indicate, the same geological agencies have been operating in the same way from the Tertiary down to the present, and generally arid conditions have prevailed, it is safe to say that during that long period the domain of the Desert Laboratory has suffered no greater, if as great, extremes of climate as prevail to-day in places no farther apart than Tucson and the Santa Catalina Mountains. It seems likely that to-day, within areas only a few miles apart, we may see floras more diverse in character than the late Tertiary and present- day floras of the Laboratory domain. As a corollary it may be assumed that, neglecting minor divisions, there have existed in this region, at least from the late Tertiary, two widely different floras, that of the plains and that of the mountains, the former of essentially desert character, the latter of mesophytic species, and that during this period, without losing at any time their distinctive features, they have, by precisely the same agencies as are operative to-day, received accessions, lost or passed on waning species, and otherwise suffered gradual modification. LITERATURE CITED. Avams, C. C. 1902. Southeastern United States as a center of geographical distribution of flora and fauna. Biol. Bull., 3: 121, 122. BaILEY, F. M. 1902. Handbook of birds of the western United States. LxxXIV-LXxxII. BAILEY, V. 1905. U.S. Dept. Agric., Biol. Sur., N. A. Fauna, 25, Biological Survey of Texas. BLUMER, J. C. 1908. Some observations on Arizona fungi. ‘The Plant World, 11: 14-17. 1908. 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Onthewater-conducting systemsof some desert shrubs. Bot. Gaz., 39: 407 1908. On the electric resistance of solutions of salt plants and solutions of alkali soils. The Plant World, 11: 11. ENGLER, A. 1882. Versuch einer Entwicklungs-geschichte der Pflanzenwelt, 2. FERNALD, M. L. 1907. ‘The soil preferences of certain alpine and subalpine plants. Rhodora, 9: 149-193. FINK, B. 1899. Contributions to a knowledge of the lichens of Minnesota. V. Minn. Bot. Stud., 2: 286-288. 1904. A lichen society of sandstone riprap. Bot. Gaz., 38: 269-279. JENNINGS, O. E. 1908. A note on the ecological formations of Pittsburg and vicinity. Science, n. s., 27: 828-830. JUMELLE, H. 1892. Recherches physiologiques sur les lichens. Rev. gén. bot., 4 : 115. KEARNEY, T. H., and Harter, L. L. 1907. ‘The comparative tolerance of various plants for the salts common in alkali soils. U.S. Dept. Agric., Bur. Pl. Ind., Bull. 113. LapHaM, M. H., and NEw, N. P. 1904. Soil survey of the Solomonsville area, Arizona. U.S. Dept. Agric., Bur. Soils. LIVINGSTON, B. E. 1906. ‘The relation of desert plants to soil moisture and evaporation. Publication 50, Carnegie Institution of Washington. 1907. Evaporation and plant development. ‘The Plant World, 10: 269-278. 1908. Evaporation and plant habitats. The Plant World, 11: 1-9, 106-112. ELovp, HL. E- 1904.