LIBRARY OF THE UNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN 5 81 .15 C59ph coo .2 Agric. The person charging this material is re¬ sponsible for its return on or before the Latest Date stamped below. Theft, mutilation, and underlining of books are reasons for disciplinary action and may result in dismissal from the University. THE PHYTOMETER METHOD IN ECOLOGY THE PLANT AND COMMUNITY AS INSTRUMENTS Frederic E. Clements and Glenn W. Goldsmith \ Published by the Carnegie Institution of Washington Washington, December 1924 i N. Y. STATE COUBrf cT*t*iCUi.TWK U/KNEU. UNIVERSITY, iihALA, K. Y CLEMENTS AND GOLDSMITH PLATE 1 O LO ii < o o 00 o UJ o Z) H LO CO LO (\j CO o CO OJ LO CD LO O O LO Ld Q =) H (- O O m (Vl Ld D D h l~ _J < oj oJ CD • • * V \ Transpiration-Temperature- r ---Wind _Evaporation-Humidity Fig. 28.—Average transpiration of sunflowers, sun station, 1923, compared with factor data. Each space equals 5 units, except for the inverted humidity curve, for which the value is 10; the base-line is 0 for transpiration, and wind and evaporation, and 25 for temperature. Light. Chemical photometers, employing a solution of oxalic acid and uranium acetate in accordance with the method of Ridgway (1918) and exposed against a uniform background and at a uniform angle in each station, were utilized for obtaining light values at the three stations on four representative days during the first series. The amount of oxalic acid decomposed during the daylight hours was used as the basis for computing the percentage of light on that of the sun station. As measured by this instrument, the light intensity in the half-shade was 45 per cent and in the full-shade 4.5 per cent of the value at the sun station, values which were too high, as shown by the stop-watch photometers employed in the second series. 60 SEASON OF 1923. Transpiration. Water-loss was constantly highest at the sun station, and it was usually higher at the half-shade than at the full-shade station, in accordance with the physical factors generally (figs. 27 to 30). The respective values per unit of leaf-area were 25, 12, and 10. The correlation of the transpiration curve with those for the factors concerned or with that of evaporation is nowhere very close, but the correspondence with their composite effect is fairly good. --Transpiration--— Temperature -Wind -Evaporation-Humidity Fig. 29.—Average transpiration of sunflowers, half-shade station, 1923, compared with factor data; values as in fig. 28. Growth. As would be expected in consequence of the dense shade, increase in leaf- area was very low at the shade station, while it was correspondingly high at the sun station, the half-shade being intermediate (plate 7). The respective values from shade to sun for the sealed phytometers were 396, 309, and 135 sq. cm. (table 17; figs. 31 to 33). The converse was naturally true of stem-length, the plants in shade and half-shade much exceeding those in the sun, the respective heights being 305, 428, and 203 mm. (fig. 32). Until the last two weeks there was little difference in the height of the phytometers in the two shade stations, but those in the dense shade finally proved too weak to support their weight and some of the tallest became so twisted and bent that they were destroyed by wind and rain before the final readings were made (plate 7). The average stem-diameter varied in the same manner as the leaf-area, being greatest in the sun (7.45 mm.), somewhat less in the half-shade (6.64 mm.), and least in the shade RESULTS. 61 (4.27 mm.). Thus, the best conditions for growth were found in the sun, as shown by both leaf-area and stem-diameter, but this was more or less obscured by the fact that elongation is more marked in the shade, resulting in taller stems in these two stations. The relation involved is best shown by the ratio between width and length of stem, which is 1 : 27 for the sun, 1 : 64 for half-shade, and 1 : 70 for full shade. While there was considerable variation between the behavior of the sealed phytometers and the unsealed checks, these were in complete agreement as to the response in each station. Dry Weight and Water Requirement. The average dry weights of the whole plants as well as of the different organs are entirely consistent for both phytometers and checks in decreasing Transpiration ___ _ Temperature __„_,_Wind - Evaporation --Humidity Fig. 30.—Average transpiration of sunflowers, shade station, 1923, compared with factor data; values as in fig. 28. from the sun to the shade station (table 18). The sole exception occurs in the half-shade stems, in which maximum length has already been noted. This does not hold for the checks, or for the whole plant or shoot, for which the response follows the sequence of the stations. For example, the average dry weight for the shoot in both phytometer and check was 1.64 grams in the sun, 1.06 grams in the half-shade, and 0.27 grams in the full shade. The average water requirement exhibited a similar relation, the respective figures being 805, 486, and 125. Soil-Air. The possible effect of the seal under the different habitat complexes was tested by removing 20 liters of air through the long tube at frequent inter¬ vals, the first liter being used to sweep the tubing free of residual air. As a further check, the analyses were always made in duplicate. The soil-air in the blank containers was regularly more nearly of the composition of atmospheric air than that found in the phytometer containers. There was 62 SEASON OF 1923. no constant difference in composition at the three stations, the carbon dioxid averaging about 2 per cent and the oxygen about 20 per cent. The former was but little different from the value found in the soil with the free checks, which ranged from 1 to 1.5 per cent at a decimeter deep. As a rule, however, the soil-air from the phytometers and the blank checks departed further from the composition of ordinary air at the two shade stations than in the sun. This was probably a result of the readier ventilation of the containers in the sun, as a consequence of the greater daily fluctuations in temperature. SECOND SERIES. Stations and Installation. The stations and the instrumental installation were the same as for the first series. Seeds from the same lot also were planted on July 5, and after a period of growth the seedlings were transferred to small containers on July 8 and sealed the following day. The transpiration per leaf-area during this time was computed for each of the 118 plants available (table 20). As with the first series, the individuals with too wide a departure in water- loss were discarded; the following were selected, placed in permanent con¬ tainers on August 2, and organized into equivalent batteries for the respective stations (table 2). Table 2. —Transpiration of phytometer plants. Sun station. Half-shade station. Shade station. No. Amount. No. Amount. No. Amount. c. c. c. c. c. c. 3. 0.68 1 0.65 2 0.66 6. .61 19 .67 9 .64 26. .61 20 .60 23 .60 28. .60 40 .64 31 .63 50. .65 47 .64 49 .63 70. .69 53 .69 54 .63 77. .62 79 .66 76 .67 99. .64 84 .63 94 .69 107. .67 101 .63 103 .60 113. .67 110 .62 108 .69 Average... .644 .643 .644 The average leaf-area of the plants in the respective batteries was 25.7 sq. cm. for the sun station, 29.2 for the half-shade, and 28.9 for the full- shade. These areas include the cotyledons, which were removed before placing the plants in the final containers and hence do not appear in the later areas. Since the cotyledons have a slightly different ratio between leaf-product and leaf-area from that of the leaves, and the rate of water- loss differs also, they were removed in the first series and the leaf-product alone considered in the initial selection. In the second series they were not removed until after the selection was made, and in consequence the leaf-area rather than the leaf-product was employed in computing the transpiration rates. SECOND SERIES. 63 Temperature. The period of the second series was slightly cooler than that of the first and was marked by an exceptionally large proportion of damp, cloudy weather. The day averages were 2° to 3° lower, but the 24-hour averages were only about a degree less, the values for the shade station being practi¬ cally identical. The day temperatures averaged 61.6°, 59.6°, and 58.2° from sun to shade, the night 53°, 51.5°, and 51°, and the 24-hour 57.2°, 55.5°, and 54.3°. However, the differences were less constant than in the first series and temperature was correspondingly less efficient in the phytometer behavior during this period (fig. 25). — Sun- Half-shade-Shade Fig. 31.—Average leaf-area of sunflowers, first series, 1923. The soil temperatures likewise showed the changed conditions due to almost continuous cloud and rain. The gravel soil of the sun station dropped from 57.3° to 45.5°, while the leaf-mold of the shade fell only 2°, from 54° to 52.2°. The average for the sun was likewise lower than in the shade, but the difference was less than a degree, while the average air- temperature was more than 3° higher at the former. This was in marked contrast to the first series. Humidity and Evaporation. The figures for relative humidity are even less significant than in the first series, owing to the fact that the hygrograph is especially erratic during very humid weather in a dry region, as a consequence of the extreme fluctuations within a few hours. While the relation between the half-shade and shade stations is normal, the latter being constantly 5 per cent higher, 64 SEASON OF 1923. there seems no logical explanation of a value 5 per cent higher still in the sun. The chief value of the results lies in showing that the humidities during the second series averaged about 15 per cent higher than for the first. On the other hand, the average wind movement was much lower for this series, being less than half as much for the sun station, where it was 5.1 miles, in contrast to 12.3 miles per day. The amount for the half¬ shade was 1.9 and for the full-shade but 0.03 mile. -Sun-Half-shade-Shade Fig. 32.—Average stem-length of sunflowers, first series, 1923. The effect of the continuously rainy weather in reducing and equalizing evaporation was marked (fig. 26). The latter was reduced more than half in the sun and half-shade stations, the respective figures for the two series being 18.5 and 8.1 c. c., and 9.8 and 3.9 c. c. The reduction was naturally less in the shade station, viz, from 5.2 to 3.4 c. c., the most significant fact being the close agreement between the two shade stations. In spite of this, the sequence of the three stations was the same in both series, namely, sun, half-shade, and full-shade. Light. The light intensities during the second series were measured chiefly by the stop-watch photometer, hourly readings being made in the three stations on a considerable number of days. The average intensity for a 12-hour day on September 2 was 0.4, 0.1, and 0.01 in terms of meridian sunlight on the same day, the relative values for sun, half-shade, and shade being 100 per cent, 25 per cent, and 2.5 per cent respectively. Noon-day values on RESULTS. 65 August 30 were 0.3, 0.15, and 0.03, while the 7 a. m. readings were 0.25, 0.07, and 0.001, and the 5 p. m. ones 0.15, 0.05, and 0.001 respectively, the greatest divergence coinciding with low altitudes of the sun. The values obtained by means of the chemical photometer were in much closer agree¬ ment with these than was the case in the first series, the relative percentages being 100 for sun, 21 for half-shade, and 3 for full-shade (fig. 37). Transpiration. The water-loss was not only highest at the sun station as for the first series, but it was also much higher for the half-shade than for the shade. The respective averages per square decimeter of leaf-area were 8, 4.5, and 1.35 grams; the sun station ranged from 1 to 7 grams more than the half- -Sun-Half-shade -Shade Fig. 33.—Average stem-width of sunflowers, first series, 1923. shade, and the latter from 2 to 5 grams more than the full-shade (fig. 27). The agreement between the curve of transpiration and that of evaporation in the sun is slight, but there is a general correlation of the former with the curves for humidity and temperature (figs. 27 to 30). Growth. When both phytometers and checks are taken into account, the leaf-area was highest at the sun station, least at the shade, and intermediate in the half-shade (plate 8). The percentage of increase was in the same order, the sun station with an average of 55 per cent being twice as high as the shade station with 25 per cent; the checks in the half-shade gave 35 per cent, the low figures for the phytometers being the result of accidents 66 SEASON OF 1923. during the last two weeks (fig. 34). The order for stem-length was exactly the reverse of that for the leaf-area, the shade station being first with 235 mm., the half-shade next with 210 mm., and the sun last with 169 mm. (fig. 35). Again, because of the inverse relation of length and width, the stem diameter varied in the opposite direction (fig. 36) , being greatest at the sun station (3.8 mm.), intermediate in the half-shade (3.3 mm.) and least in the full-shade (2.6 mm.). With a single exception, the unsealed phy- tometers or checks gave higher values than the sealed ones, indicating that the growth of the latter during such a humid period may have been retarded by faulty aeration. However, this is hardly confirmed by determinations of the composition of the soil-air; the amount of carbon dioxid was usually highest in the half-shade, intermediate in the sun, and least in the full-shade. The amount varied from 0.6 per cent to nearly 4 per cent, the blank checks usually yielding about four-fifths as much as the phytometers. Fig. 34.—Average leaf-area of sunflowers, second series, 1923. Dry Weight and Water Requirement. The average dry weights again decreased in the order of the stations from sun to shade, the single exception being that phytometer roots in the half-shade gave a higher value than in the sun (table 18). The respective values for the three stations for the whole phytometers were 1.03, 0.98, and 0.41 grams, and for the check shoots 0.82, 0.37, and 0.26 gram. For the sun and half-shade stations the dry weights were only about half those for the first series, while for the full-shade they were slightly higher, the differ¬ ences between the stations being consequently much smaller. This is reflected in the water requirement, the demands for water in sun and half¬ shade being only about a fifth as much as in the first series, and in the full-shade about half as much. The values in the order of the stations were 165, 94, and 59. SHORT-PERIOD PHYTOMETERS. The short-period phytometer is one that is operated for a few hours or days in contrast to months or an entire season. It regularly makes use of a single function, such as transpiration, instead of more complex ones, such as growth or yield. Growth and short-period phytometers are comple¬ mentary, but the latter are so much simpler to install and operate that they have a much wider usefulness for the solitary investigator. Their advan¬ tages are many, by virtue of the simpler equipment needed, the briefer period of exposure, and the utilization of single functions. In the matter of equipment, the containers may be smaller and lighter, and hence more easily transported, since the plants do not remain in them for a long period Fig. 35.—Average stem-length of sunflowers, second series, 1923. and there is less risk of their becoming root-bound or suffering from deficient aeration. Sealing is a much simpler and more certain process, and there is less danger of cracking and consequent absorption of water. The smaller containers make it possible to use smaller and more portable bal¬ ances and permit greater accuracy in weighing, owing to the reduced load. The short period is especially advantageous in reducing the chance of accidents of all sorts, particularly from wind and hail. It avoids, or at least minimizes, undesirable changes in the soil-air in consequence of the seal and insures much more normal growth and behavior. It renders it possible to expose the plants to uniform conditions or to a desired set, and avoids the complication of a sudden change in factors. A marked advantage resides in the fact that an abnormal season can not convert an expensive and time-consuming seasonal installation into a more or less com¬ plete disappointment, as happened in 1923 at the Alpine Laboratory. The short-period phytometer enables one to employ plants at any stage of 67 68 SHORT-PERIOD PHYTOMETERS. development and to select uniform individuals with the minimum effort; the periods can be regulated so that growth enters little or not at all as a dis¬ turbing factor. The periods permit the closest analysis of behavior with respect to any particular function, intervals of a few minutes being as feasible as those of hours or days. However, it must be recognized that the closer the scrutiny, the more exacting the schedule of weighing, or meas¬ urement, and factor determinations. Finally, an expensive installation of recording instruments is much less necessary, since simple thermometers, psychrometers, photometers, etc., are fairly adequate. Applications. The short-period phytometer can be employed to advantage in any problem not too remote from a base, but its greatest usefulness is where simple functions are concerned rather than growth or yield on a large scale. Even in the latter, however, it is an all but indispensable adjunct of seasonal pbytometers, as it permits readier and more exact analysis of the factor- function complex. Within these limitations, it should be utilized in all projects and experiments where instruments are used, since the interpre¬ tation of instrumental data must remain misleading, incomplete, or imperfect without phytometers. This means that short-period phytometers are not only necessary, or at least desirable, in all studies in natural or cultural habitats, but also in control experiments in greenhouse or labora¬ tory, and as much or even more in investigations in such applied sciences as agronomy, horticulture, forestry, grazing, etc. Of all the functions that can be employed as measures, transpiration is by far the most satisfactory; partly because it can be readily and accurately determined without placing the plant under abnormal conditions, and partly because of the basic importance of the water relation as well as its great variability. In these respects, photosynthesis as measured in terms of photosynthate stands next, but this method still leaves much to be desired in the matter of accuracy, while the gas method necessarily modifies habitat factors seriously. This is likewise true of the use of respiration as a measure, and the latter also suffers by having no such direct relation to water or light. Germination may be utilized as a measure of the chresard and of surficial soil-temperatures. Movements have also been employed, as in the case of the opening and closing of flowers, carpotropic movements, the opening and closing of stomata, etc. Methods. The selection of species for use as short-period phytometers is determined largely by the object in view and the function to be utilized. In the case of comparative studies, standard plants such as sunflower and beans are to be preferred, while in the accurate interpretation of relations it is often desirable to make use of the very species to be investigated, such as wheat, corn, alfalfa, native grasses, forbs, 1 etc. Special qualities and conditions 1 The term “forb” is here used for herbs other than grasses in order to afford a clear cut dis¬ tinction and at the same time avoid an awkward phrase. It is derived from the Greek-Latin root which appears in and in herba (*ferb—). METHODS. 69 must often be taken into account likewise; for example, in the present series made toward the end of the season in the montane zone, Cyclamen proved the most satisfactory of the several species available, owing to the nature and position of its leaves. The individual plants should be selected on the basis of similarity in behavior as determined by actual measurement under uniform conditions, and in the case of longer series this should be checked, preferably at the end of the experiment. Converting the plant into a phy¬ tometer is a much simpler matter than previously indicated, an impervious container of convenient size and a wax seal sufficing in most cases. When the period covers several days or more, especially under strong insolation, Fig. 36. —Average stem-width of sunflowers, second series, 1923. a tube is required for watering and aerating the soil. The minimum num¬ ber of plants for a battery should be 3, though 5 or 10 insure better results. The plants are grouped in each spot in such a way as not to affect each other, but to be under essentially uniform conditions, though when the latter vary considerably it is sometimes better to scatter the plants. When the installation is a large one in distinct habitats, recording instruments are all but indispensable, but in the more intimate analysis with short-period phytometers, the thermometer, psychrometer, atmometer, anemometer, photometer, and geotome suffice in the great majority of cases. Short-period phytometers lend themselves most readily to hourly determinations through the day or daily ones for a week or so, as well as to the obtaining of morning and afternoon or day and night values. Obviously, intervals of a half-hour or less or 2 to 3 hours are often desirable. When the period is longer than a week or 10 days, the container must be 70 SHORT-PERIOD PHYTOMETERS. larger and the phytometer made with greater care, so that it approaches the growth type in many respects. The detailed application of the method is of the widest, ranging from transpiration and other measurements in distinct climatic or serai habitats at the one end to the detailed analysis of minute habitat areas at the other. It has been employed for measuring the efficient factors in sun and shade, at different altitudes, on opposite slope- exposures, in different forest layers, in the shade or in the crown of different- shrubs and trees, above various covers or soil surfaces, at different angles of slope, etc. In short, it gives results of value wherever factor differences exist. -- Sun -Shade -Ha If-shade Fia. 37.—Light intensity in terms of meridian sun, August 26, 1923. Installation for 1923. The continuously rainy summer interfered with the experiments planned for short-period phytometers, and favorable sunny conditions were avail¬ able only in September and near the close of the season. This limited the choice of species in the first place, and practically all of these except Cycla¬ men were eliminated by snow and hail. The thick, semi-fleshy leaves of the latter made it especially adapted to late-season studies, and they possess the further advantages of being nearly entire, horizontal, and on much the same level. The instrumental installation was maintained in the three major phytometer stations, and this served also as a background for readings by means of simple instruments in the temporary stations. The plants were transferred to impervious pots, watered and sealed, and then given a day or two for adjustment before being used. Plants of moderate RESULTS. 71 size were selected, particular care being taken to see that all the leaves were normal and freely exposed. The pots employed were 4-inch paper ones previously coated with paraffin and sealed by means of a collar of plasto- cene clay about the plant and a layer of paraffin melting at 56° over the soil surface. Weighing was done on a torsion balance with a capacity of 4.5 kg.; this was kept indoors in a neighboring laboratory to avoid various minor disturbances. In the temporary stations readings of light and tem- Sept. 18 9-11 11-1.30 130-3 3-530 X - \S N\ \v ■ ■ ■ . _Sun ____-.Shade -Half-shade Fig. 38.—Average transpiration per leaf prod¬ uct (light lines), and average evaporation (heavy lines); short-period phytometers, Sep¬ tember 18, 1923. Fig. 39.—Average transpiration per leaf prod¬ uct (light lines), and average evaporation (heavy lines); short-period phytometers, Sep¬ tember 20, 1923. perature were made at frequent intervals, and evaporation was determined by means of white cylindrical atmometers run in duplicate, the readings being averaged and reduced to standard. Sun and Shade. Batteries of four Cyclamen phytometers were installed in each of the three main stations, sun, half-shade, and shade, on September 16. The plants were exposed at 11 a. m. after being weighed and were removed and weighed again at 4 p. m. The average hourly loss divided by the leaf- product gave the relative values of 37 for the sun, 16 for the half-shade, and 9 for the full-shade station, the respective percentages being 100, 44, and 24 72 SHORT-PERIOD PHYTOMETERS. (table 21). The same batteries were again exposed on the 18th and weigh¬ ings made at four intervals from 9 a. m. to 5 h 30 m p. m., from which the hourly loss was computed. The hourly loss was again more than twice as great in the sun as in the half-shade and about twice as much for the latter as for the full-shade (fig. 38; table 22). In general, a similar relation obtained between the evaporation at the three stations; this was in har¬ mony with the light and temperature readings, with the exception that the shade station was slightly warmer than the half-shade. 40 35 30 25 20 15 10 5 0 -_North -—South Fig. 40.—Average transpiration per leaf product (light lines), and average evaporation (heavy lines); short-period phytometers, September 26-27, 1923. On September 21 all the phytometers were placed on level gravel soil in full sunshine from 9 h 40 m to ll h 40 ra a. m. to determine the individual variability and to permit grouping them in batteries of similar average loss (table 24). They were then exposed in full sun, half-shade with many sun-flecks beneath birch (Betula occidentalis ), and deep shade under spruce (•Picea engelmanni), where there were no sun-flecks and practically no ground cover. The respective values were 120, 48, and 11, the percentages being 100, 39, and 9. Evaporation was relatively more marked in the shade stations, the respective percentages being 55 and 29. This is readily explained by the fact that the differences in temperature between the three stations were small, while the light intensity decreased greatly. fl . 30 _ Sept. 26-27 6p.m.- 11:30 a.m. ir.45-3 p.m. 3-6p.m. 6 : 45 a.m. / 7 / 1 \ / / / \ \ \ \ \ \ _^_ / / \ \ \ A < / / / / / \ X X \ \ N Ax RESULTS. 73 Surface, Slope, Exposure, and Altitude. Four batteries of Cyclamen phytometers were installed within a few yards of each other in as many different situations on September 20. Two were placed on the level, one in a short bluegrass turf, the other on bare gravel; the other two were put on a bare gravel-slope facing the south. In one the leaves were maintained in the usual horizontal position, while in the other the plants were shifted each hour to keep the leaves at right angles to the sun’s rays. An unexpected disturbing factor entered by virtue of the fact that the phytometers on the bare gravel wilted somewhat during the middle of the day, and this resulted in a decrease in the rate of transpiration. Hence, while the phytometers gave conclusive evidence of the more xerophytic conditions above the gravel, this appeared in the figures for transpiration only during the first and last period (fig. 39; table 23). On the contrary, evaporation above the gravel was slightly lower than for the turf during the first period, but it then rose more rapidly and was more than twice as great from 3 h 30 m to 4 h 30 m p. m. The phytometers with the leaves at right angles to the sun’s rays gave a consistently higher water-loss throughout the day, the divergence from the horizontal leaves naturally becoming greatest in the last period, when the angle of incidence was smallest. Evaporation was highest on the gravel slope, owing to its south exposure, but it also fell off markedly during the last period. Short-period phytometers of Cyclamen were run on north and south slope- exposures of Engelmann Canyon at the Alpine Laboratory from 8 h 30 m a. m. September 26 to 6 h 45 m a. m. September 27, the distance between the two stations being about 100 yards. As was to be expected, the south exposure was found to be both drier and warmer than the north throughout the day and night, though the temperature difference at night was naturally much smaller. The general agreement between temperature, light, and evaporation on the one hand and transpiration on the other was good, the curves of the latter being flattened by the fact that maximum light intensity came much earlier in the day than the maxima for temperature and evaporation (fig. 40; table 25). On September 22, batteries of Cyclamen phytometers were exposed simultaneously in full sunshine at the Alpine Laboratory, 8,100 feet, and at Windy Point on Pike’s Peak at an altitude of 12,500 feet. In spite of considerable differences in temperature, the transpiration and evaporation were nearly the same, being only slightly greater at the lower elevation. This is in contrast to earlier studies (Clements, 1908), which gave higher values on alpine summits, evidently in response to reduced air-pressure, and is probably to be explained by the prevalence of snow at this late date. RELATED APPLICATIONS OF THE PHYTOMETER METHOD. SLOPE-EXPOSURE STUDIES. The marked differences of vegetation on opposite slopes have often been noted, but no comprehensive and thoroughgoing analysis of the physical factors, growth relations, and community behavior had been made before the present study (Clements and Lutjeharms, 1921-1923; Lutjeharms, 1924). In mountain regions of the West in particular, the difference between northerly and easterly slopes on the one hand and southerly and westerly ones on the other may amount to a whole climax, the dry-warm slope being subclimax to the general climax or the moist-cool slope exhibiting Maximum- Maximum- Minimum-Minimum---- Fig. 41. —Comparison of air and soil temperatures on north (light lines) and south (heavy lines) slope-exposures, Alpine Laboratory. a postclimax (Plant Succession, 109; Plant Indicators, 88). Such relations are fundamental to the investigation of changes of climate and vegetation, and hence to the phylogeny of climaxes. They have come to play an increasingly important part in the comparative evolution of formations and 74 SLOPE-EXPOSURE STUDIES. 75 associations, and this has rendered it advisable to employ definite terms for the two types of slope-exposure, especially since the terms drawn from direction are often awkward and their significance is reversed for the northern and southern hemispheres. Regardless of exposition, the dry-warm slope is designated the xerocline (£ 77 / 06 ?, dry; *AiW slope) and the moist- cool slope the mesocline (/ueo-o?, mid, hence moist). Installation. An unusually favorable opportunity for slope-exposure studies was afforded by Engelmann Canyon, in which the Alpine Laboratory is situated. This is a long, narrow canyon on the east slope of Pike’s Peak, extending from the foothills at 7,000 feet to an altitude of 9,000 feet. In consequence, 14 13 12 ii 10 9 8 7 6 5 4 3 2 I 0 it has constituted a highway for the movement of grassland and plains species upward along the xerocline during dry phases of the climatic cycle and of montane and subalpine ones downward during wet phases. In the vicinity of the Laboratory to-day, the north exposure is covered with a practically pure forest of Douglas fir ( Pseudotsuga mucronata) , while the south exposure is a mictium of grassland and chaparral, dotted with yellow pines ( Pinus ponderosa ), scattered Douglas fir, and occasional limber pines (Pinus fiexilis). Extensive thickets of chaparral, consisting chiefly of Quercus, Holodiscus, and Primus, occur in the more stable areas, but for the most part the slope is occupied by an open bunch-grass community of Elymus triticoides, Muhlenbergia gracilis, and Andropogon scoparius , with Mesocline __ Canyon bottom __ Xerocline 13 37 'O': 3(18) io: ■ 5 9.9(22)'t 24 9. T (2 695 08) 706 686 (Z7) 72 Z ,6.6 (22) 5.9 (26) 5.5 (22) 4. 6(18) 37 ■ .0 3G>3. _ 188 183(4) 125 (4) 137 ■ • J | 86 (4) June July August June July August June July August _—^i Total miles-wind velocity .. Evaporation-cc. mum a Grams oxalic acid oxidized by light C ) Numberof days when less than a month Fig. 42.—Monthly value for wind, evaporation, and light in slope-exposure transect. 76 RELATED APPLICATIONS. relict areas of Agropyrum glaucum, Bouteloua gracilis, and Elymus cana¬ densis, and numerous subdominants from the plains. Fig. 43.—Comparison of holard percentages in slope-exposure transect; south slope-exposure (heavy lines), north (medium lines), bottom of canyon (light lines). Two stations were located directly opposite each other, at a height of about 500 feet above the bottom of the canyon, where the third station was installed near the brook. Complete batteries of instruments were placed in each of the stations and continuous records obtained of the following SLOPE-EXPOSURE STUDIES. 77 factors: (1) air-temperature, (2) soil-temperature at depths of 4 and 12 inches, (3) relative humidity, (4) evaporation, (5) wind, (6) light intensity, (7) precipitation, and (8) holard. Several native and cultivated species, including some shrubs, were employed as phytometers, but the best results were obtained with the sunflower. The functions utilized were transpira¬ tion, photosynthesis, and growth, in terms of stem-height, diameter, leaf length and width, dry weight, and water requirement. The detailed results of the investigation are now being published (Lutjeharms, 1924), and a brief summary will suffice here. Summary. The efficient factors gave the following differences for the xerocline in comparison with the mesocline (figs. 41 to 43). Air-temperature (average of maximum and minimum readings).+ 2° Soil-temperature (average of maximum and minimum readings).+11° Average daily soil-temperature at 12 inches..+16° p. ct. Light, evaporation, and wind, each approximate.+ 50 Average humidity.— 6 Holard at 0 to 6 inches.— 36 Holard at 6 to 18 inches.— 26 The transpiration and growth of phytometers during the entire season gave the following values for the xerocline (plate 9; figs. 44, 45): p. ct. Average leaf-area per phytometer.+ 14 Average stem-diameter per phytometer.-J- 10 Average stem-height per phytometer.— 25 Average dry-weight per phytometer.+ 75 Average transpiration per phytometer.+ 82 For phytometers grown half as long and during the latter part of the summer, the values were as follows: p.ct. Average leaf-area per phytometer.+ 71 Average stem-diameter per phytometer.+ 10 Average stem-height per phytometer.— 13 Average dry-weight per phytometer.+ 38 Average transpiration per phytometer...+130 Average carbohydrate reserves in milligrams of dextrose.+ 32 The preceding instrumental and phytometer results make it clear why the south slope-exposure is covered with the scrub and grassland dominants of foothill and plains, while the north one is dominated by the charac¬ teristic montane forest of this climatic zone. They also serve to explain the reason for the dry-phase invasion along the xerocline and the wet-phase movement down the mesocline, as well as in the bottom of the canyon. Transpiration and Growth in the Grassland Climax. PHYTOMETER BATTERIES. In order to obtain further light as to the climatic differences of the major stations in terms of functional response, a special investigation was made of transpiration and growth (Clements and Weaver, 1924). Plants of Helian - thus annuus, Avena sativa, Elymus canadensis, and Acer negundo were grown from seed or transplanted as seedlings into sheet-metal containers of appro- Dry weight-Transpiration Fig. 44. —Average dry weight and transpiration of phytometers in slope-exposure transect; south slope-exposure (heavy lines), north (medium lines), bottom of canyon (light lines). priate shape and sufficient size to accommodate the root systems through¬ out the duration of the experiment. After the plants were well established, the leaf-area and the weight of plant and container were determined. They were then installed at the several stations, together with a complete battery of instruments, for a period of 14 days, and measurements made of tran¬ spiration and growth in terms of increased area. The considerable differ¬ ences in altitude, and hence in seasonal development, made simultaneous studies undesirable, and consequently the periods of observation were suc¬ cessive. This was also imperative because of the time and effort involved. 78 TRANSPIRATION AND GROWTH IN THE GRASSLAND CLIMAX. 79 The individual plants of sunflower and box-elder were placed in cylin¬ drical galvanized-iron containers 5 to 6 inches in diameter and 9 to 10 inches deep, filled with rich loam soil tamped firmly in place. A layer of 0.5 inch of coarse gravel in the bottom of the container covered an exit tube, consisting of an automobile tire valve-stem with the inner end cut off and covered with a fine copper gauze soldered in place. The core of each tube had been removed. The tube was soldered in place with the threads pro¬ jecting through the wall of the container, so that an exhaust-pump could be attached for aerating the soil. The tube also assisted materially in water¬ ing the plants, the usual cap preventing loss during the intervals. The soil was well screened, brought to an optimum holard, and weighed at the time of filling the containers. By restoring the containers to their original weight from time to time, the holard was maintained at the desired level. To Mesocline _ Canyon bottom __ Xerocline 7.9 8.7 7. 7 7 13 6 'i fee >5 6' L8 51 A 496 5.5 4' » 4< 30 3.3 3< 36 ! £.4 1/ 11 0 f 3 1! 0.47 1 T . Leaf area (Sq.cm.) tixuuLiiui-n-ji Transpiration per. gm.dry weight Stem height (mm.) >— .. * Dry weight of tops Stem diameter (mm.) Dry weight of roots Fig. 45.—Comparative growth and dry weight of phytometers in slope-exposure transect. prevent loss other than by transpiration, the containers were furnished with a sloping metal top provided with a circular opening, with the edges reamed upward, and large enough to receive a cork 2.5 inches in diameter. An effective seal was formed by boring a hole large enough for the plant stem, splitting the cork and fitting it into place after padding the sides of the opening with a little cotton. The seal was tested by a check container with¬ out a plant but fitted with a wooden peg to simulate the plant stem. During the period of 14 days this did not lose water in an amount sufficient to be detected by a balance sensitive to 2 grams under a load of 7 kg. The containers for wild rye and oats were similar to those already de¬ scribed, except for the tops, which were furnished with a slit 5 inches long 80 RELATED APPLICATIONS. and 1 inch wide. The edges of the metal cut in making the slits were turned down into the container about a quarter of an inch on each side and a half-inch at the ends of the slit. These furnished supports for narrow strips of shellacked oak, which were held in place by thin wedges of similar material at each end. These were put in place after the containers had been filled and the soil pressed firmly under the metal tops. They were then coated with shellac so that no openings remained except between the wooden strips, which narrowed the slit to about 10 mm. The seeds were planted through this opening, which was nearly filled with soil kept moist by frequent watering. After the plants came up, the remainder of the opening was filled with sand level with the top of the wooden strips. The containers were provided with felt tops, cut to fit around the slits, and sunk level with the soil. The efficiency of the sand-mulch in preventing water- loss was found to be high, only 6 grams escaping in a period of 2 weeks. Twelve plants of average size were selected from the several containers and Table 3. —Transpiration and growth at the three stations. Species. Water-loss per sq. dm. Increase in area. Rate of growth, based on actual increase in area Lin¬ coln. Phil¬ lips¬ burg. Bur¬ ling¬ ton. Lin¬ coln. Phil¬ lips¬ burg. Bur¬ ling¬ ton. Lin¬ coln. Phil¬ lips¬ burg. Bur¬ ling¬ ton. gm. gm. gm. p. ct. p. ct. p. ct. p. ct. p. ct. p. ct. Sunflower. 145 225 214 409 1,477 4,097 854 860 998 Wild rye. 72 199 218 239 257 163 410 549 140 Oats. 99 178 212 279 246 694 1,155 796 510 Box-elder. 85 159 137 85 162 220 52 161 370 Average. 100 190 195 253 535 1,294 618 591 504 the leaf-area determined. From this, and the number of plants in each container, the initial area of the group of plants in any container was calculated. The final area was determined in a similar manner. This method was used because it was quite impossible to determine the total area of the plants in place, as could be done with the dicotyls. Owing to cool, wet weather the plants grew slowly, except during the last week of May. They were kept covered during rains and at night, watered from a burette, and aerated from time to time. To keep the metal containers from heating the soil, they were surrounded by sand and the top covered by a collar of felt about a centimeter thick, held in place by strips of adhesive tape. On June 1 the leaf-area was determined by means of solio prints and the planimeter, corks were inserted, and the containers (with collars removed) brought back to their initial weight after they had been transported to the stations in the high prairie at Lincoln, and at Phillipsburg and Burlington. Here they were placed in the soil and thoroughly covered after the collars had been replaced, the exposed plants being sheltered during rains. SOD-CORE PHYTOMETERS. 81 After the 14-day period of the experiment, following final weighings, the number of parent plants and number of tillers in each container was ascer¬ tained. Eighteen specimens of each group were then selected and their areas determined. From these data the final areas were calculated. This series proved a disappointment in so far as normal climatic rela¬ tions were concerned, owing to the wholly exceptional weather. The amount of sunshine at Lincoln was little more than half that at the other stations, while the air-temperature averaged 10° lower and the soil-temperature ranged from 11 to 15° lower. The average humidity was 15 to 18 per cent higher and the evaporation but a third or a fourth of that at Phillipsburg or Burlington. Hence, it is easy to understand why the increase in area was twice as great at Phillipsburg and more than four times as great at Burlington, though the normal relation is suggested by the rate of growth Table 4. —Environmental conditions at the three stations. Station. Approxi¬ mate hours sunshine. Average day tem¬ perature. Soil temper¬ ature. Average day humidity. Average daily evaporation. Wind, miles per hour. 0 F. o p p. ct. c. c. Lincoln. 39 70.1 62 to 71 75 8.4 3.6 Phillipsburg.. . 75 80.6 74 to 82 60 25.5 3.3 Burlington.... 71 80.0 73 to 86 57 35.4 3.4 based on the actual increase in area and by the order of water-loss at the three stations. Thus, while the plant responses are in agreement with the physical factors for the respective fortnights concerned, it is obvious that entirely comparable results could be insured only by dealing with the growth season for each species. An adequate record of transpiration and growth for such a period at station^ widely separated demands at least one resident investigator for each station, and such studies must await the future. COMMUNITY PHYTOMETERS. Sod-Core Phytometers. One of the major tasks of quantitative ecology is to determine the func¬ tional responses of plants when grouped in communities. While much light can be obtained by the use of individual plants under control in the field, in the form of standard phytometers, these differ essentially in their soil and competition relations from plants growing together in the actual cover. Hence, the task is to maintain these natural relations of the community and at the same time to secure a degree of control that modifies the efficient factors little or not at all. In the case of transpiration, for example, these requisites can be met only by weighing, as all other methods modify the physical factors to an undesirable degree. The method that maintains the soil and community relations with the minimum disturbance is the soil- block, which was first employed for determining the chresard in the field (Clements, 1904, 1905). This requires only such slight modifications as those of size and form to become applicable to all problems in which an undisturbed soil-root core is indispensable (Weaver and Crist, 1924). 82 RELATED APPLICATIONS. In consequence, the first objective was to perfect the soil-block method so that it could be used in the field with both convenience and accuracy. Because of its importance in the grassland climate, the chief function to be measured was transpiration, though chresard and aeration can be studied with something of the same readiness. In the present case the transpira¬ tion from representative cores was followed in the proper climate of each association, but it is evident that the containers can be moved or exchanged between different edaphic or climatic stations and thus serve as reciprocal phytometers. This permits the determination of the transpiration behavior of each climax in its own climate in terms of adjustment and adaptation and at the same time affords a basis for comparing adjacent climaxes. A further use of fundamental value arises out of the rainfall relation. The method of the soil-core not only makes it possible to trace the complete water cycle of rainfall, holard, evaporation, and transpiration, but also to estimate the extent to which the vegetation of each region may furnish the water-vapor for its own rainfall (Clements, 1923). Finally, it also opens up a new field in the functional relation of roots to the soil as an actual structure, which shows striking differences from climate to climate, as well as from one local habitat to another. Methods. A steel cylinder 12 inches tall and with an inner area of 1 square foot, the lower edge of which was sharpened, was driven into the grassland soil to a depth of 4 inches. Care was taken to cut off none of the leaves belonging to the plants in the square foot selected, which was chosen with a special regard to its representative structure. The cylinder was then carefully removed, leaving the column of soil intact, and replaced by one of heavy galvanized iron 3 feet long and reinforced at both ends by a heavy wire over which the metal was turned back smoothly. After starting a row of these cylinders at distances of 8 inches, a trench 2 feet wide was dug around them to a depth of over 3 feet. In this process no soil was removed within 3 or 4 inches of the cylinder. As the trench was deepened, the columns of soil were carefully pared away with large knives in such a manner that the cylinders could be forced down under considerable pres¬ sure from above. By shaping the column for a few inches in front of the descending cylinder, it was possible to force the latter into place over a tightly fitting soil-core to a depth of 3 feet. The columns were then undercut and smoothed off level with the lower end of the cylinder. A loose-fitting metal bottom with the edges 2 inches deep was placed over the end and the entire container was then weighed on a portable Fairbanks scale sensitive to one-fourth pound. In the meantime a trench sufficiently wide and deep to receive the cylinders in an upright position had been dug in a nearby area, care being taken not to cover the grass with soil. The containers were lowered in the new trench and slid into place on a plank in the bottom, after which the bottoms were made water-tight by means of a measured amount of hot wax of the usual composition. The trench was then filled with soil and nieces of sod were fitted around the tops so that the surface conditions would be essentially normal. The trenches were selected so that the SOD-CORE PHYTOMETERS. 83 surface-water would readily drain away from them, and in addition the plants were covered by wooden roofs whenever rain was actually falling. This was imperative because of the varying interception of rainfall by the different vegetation in the several containers. In the case of the cultivated crops, oats and millet, the usual type of bottom was replaced by one 3 feet deep, owing to the difficulty of selecting a proper slope for drainage. In order to determine the amount of water evaporated from the cultivated soil, the plants were removed from one container in each field. In another the natural grasses were left in place after having been killed by the addi¬ tion of a measured amount of boiling water (plate 10a). Table 5. —Comparison of factors and average water-loss. Station. Dominant grasses. Date of experiment. Approxi¬ mate sunshine. Aver. day temp. Aver. day humidity. Aver. daily evapo¬ ration. Aver, daily loss from sq. foot of cover. Burling- (Bulbilis. p. ct. o F p. ct. c. c. lbs. ton... . s Bouteloua. .. 1 Agropyrum. . •July 5 to 20. 71 80 57 35.4 0.96 Phillips¬ burg. . . (Bouteloua. . . (Andropogon.. Andropogon.. June 18 to July 3. 75 80.6 60 25.5 1.33 Lincoln.. Stipa. ' Koeleria. Bouteloua. .. July 24 to Aug. 8. 47 79 80 22.0 0.85 From time to time, depending upon the weather and the needs of the plants, water in measured amounts was slowly added to all the containers, and as a result there was little shrinkage of the core from the sides of the container. None of the plants died, and even those near the edges gave no signs of wilting, demonstrating that the roots in the core supplied abundant water for transpiration. Much care was exercised in watering, so that there was little or no runoff down the sides of the core. This was accomplished by pouring the water on slowly and pressing the moist soil firmly against the cylinder wherever the contact was not complete. At the end of the period the containers were again weighed and the losses calculated. At the end of the experiment the vegetation was carefully removed at the soil surface by means of a hand grass-clipper. The dense foliage of former years was carefully separated from the living plants, the latter oven-dried at 60° C., and weighed. Results. As in the case of water-loss from the phytometers, the exceptional weather of the summer obscured the normal climatic response of the sod-cores. When the physical factors and the type of vegetation are taken into account, it is clear why the low short-grass cover at Burlington in the driest climate transpired less than the mixed prairie at Phillipsburg in a moister atmos¬ phere and more than the luxuriant true prairie at Lincoln in a much more humid climate. Thus again, while the use of sod-cores contributed no clear-cut evidence as to the relation of the three climaxes and their climates, it does demonstrate the value of the method and what can be expected of 84 RELATED APPLICATIONS. it when employed through a series of years. The losses from the three crops, while of interest, have no comparative value, since a different species was used in each station; they are distinctly helpful, however, in showing the similarity in the behavior of the native cover and representative crops for each station and in potential importance for the rainfall of each region. However, in the future development of the method, it is obvious that the same dominant and the same crop should be employed throughout the series of stations, and this should involve the reciprocal transfer of sod-cores and crop-cores between the three stations. FIELD-PLOT PHYTOMETERS. The field-plot and cut-quadrat phytometers have much in common when the latter is used for cultivated plants, the chief difference being the greater size of the former. The field-plot type was utilized in 1922 and 1923 for measuring the conditions in dry-land farming and in irrigated fields in terms of root behavior and yield. The installation was made at Greeley, Colorado, in plots of one-thirtieth acre in fully irrigated, partly irrigated, and dry land. The crops employed were alfalfa, spring wheat, sugar beet, potato, and yellow dent corn. Complete records were kept of the usual factors, except wind, and the holard was determined weekly to a depth of 4 feet and at longer intervals to the depth of root penetration, 5 to 9 feet. As the dry-land and irrigated areas were only about a mile apart, the general climatic conditions were identical and the soil was similar, the efficient differences arising out of the irrigation. The development of the root system was traced at several intervals during the growing season, growth of shoots measured from time to time, and the yield determined at the end (Jean and Weaver, 1923, 1924). In every case the root development and habit were found to respond closely to variations in the holard, and the crops with the most extensive root systems to give the largest yields. The general root behavior may be illustrated by wheat, the roots of which spread more widely in the surface soil owing to showers, but died below 2 feet in dry soil, the corresponding penetration being 3 feet in lightly irrigated and 4.3 feet in fully irrigated soil. The plots were at first equally moist in 1923, and the root systems were alike; because of greater rainfall the penetration in dry land was a foot greater than in 1922, while growth in the irrigated plots was much the same as before. The respective heights in dry land, partially and fully irrigated plots were 15, 41, and 43 inches and the yields 3, 32, and 29 bushels. The roots of corn made the best development in the lightly irrigated plot, and this was correlated with the best yield of 125 bushels per acre, the yield being 25 bushels for dry land and 115 for full irrigation. CUT-QUADRAT PHYTOMETERS. The growth of a representative area of a community may be used as a climatic index as well as a measure of response in much the same way as transpiration. It possesses three distinct advantages over the latter, though the two are complementary and hence one can not replace the other. Growth demands no laborious installation, as it can be determined directly from the native or culture community in position. While it can be measured at CLIP-QUADRAT PHYTOMETERS. 85 any time, it yields the major values at the end of the growing-season, and thus does not require the services of a resident investigator. Moreover, it integrates the response for the whole season, though as a complex it permits less ready analysis than transpiration and is also less satisfactory for short periods. In short, it is the simplest and most convenient of all community phytometers when employed in the form of the cut or clip quadrat. This is the only practicable method, as the measurement of the individuals in a community group is too time-consuming to be desirable. There are certain cases in which it is profitable to pull the individuals out with their roots, but this is hardly feasible in a close cover or a compact soil. The clip- quadrat is merely the usual one of a square meter in extent, from which the shoots are cut at any desired time. It may be either smaller or larger in order to meet special conditions, as in the case of crops planted in rows. The growth is regularly expressed in terms of dry matter, but in the case of grazing ranges or forage crops, the green weight should likewise be found. Finally, the clip-quadrat facilitates the analysis of community response to climatic factors by making it possible to measure growth during different portions of the season or its variations from season to season or from the wet to the dry phase of a climatic cycle, and to determine the part played by the various species in the total production. In the case of the grains, it is often preferable to select the individuals to be cut in accordance w r ith the results desired, instead of taking all those in a particular area (Weaver, Jean, and Crist, 1922). This may be regarded as an aggregate clip-quadrat; it has the further advantage of permitting measurement of particular individuals throughout the season. Clip-quadrats were first installed at the three stations in 1920; these rep¬ resented high and low prairie in the true-prairie association, mixed prairie, and short-grass plains (Weaver, 1924). They were again cut in 1921 and 1922 to determine the fluctuation from year to year. The first step in the simple procedure was to select a considerable number of quadrats in typical areas of each climax. The height and density of the cover, the abundance of dominant and subdominant species, the presence of layers, etc., were recorded and photographs made of certain of the quadrats. In some instances it has proved desirable to make a chart of these as well. The cover was then removed by cutting it near the surface and at a uniform level with a hand-clipper. It was collected, sorted, and then shipped into the laboratory to be thoroughly air-dried, after which the actual production was determined on the basis of the dry weight. This gave an expression of the growth of the community as a unit, as well as the role taken by each dominant or subdominant in this. As complete factor records were obtained at each station, this made it possible to correlate the yield of community or species with the climate and the season at each (plate 10b). Since even the most uniform cover shows some variation in density, the clip-quadrats were selected with much care and in sufficient number to insure dependable results. As in all ecological studies that are adequate, i. e., causal and quantitative rather than merely mathematical, this demands considerable knowledge of the community and can not be met by random selection. The best plan is to locate a proper proportion of quadrats in 86 RELATED APPLICATIONS. pure or nearly pure stands of each dominant whenever these are present and to distribute the others among the various mixtures. It is often desir¬ able to take the subdominants into account in doing this, as their yield may be much greater than that of the grasses. Results at Grassland Stations. In every case each grass or mixture of grasses yielded progressively less as the rainfall and holard decreased to the westward. The only exception is the case of buffalo-grass at Lincoln in 1921, and this is readily explained Table 6. —Average yield of clip-quadrats , in grams. Dominant type of vegetation. 1920. 1921. 1922. Lin¬ coln. Phil¬ lips¬ burg. Bur¬ ling¬ ton. Lin¬ coln. Phil¬ lips¬ burg. Bur¬ ling¬ ton. Lin¬ coln. Phil¬ lips¬ burg. Bur¬ ling¬ ton. Buffalo-grass. . . Wheat-grass. . . . Mixed short and tall grasses. . . 290 541 313 410 98 500 197 235 606 266 457 207 400 541 260 334 365 287 179 263 Mixed tail- grasses . Average, based on number of quadrats. i 458 755 477 413 458 378 183 603 402 353 447 311 224 as an effect of grazing. Moreover, the averages for each year at the several stations show a graduated series, plant production increasing with increased efficiency of rainfall. However, it may be readily seen that the total yield at all of the stations was greater in 1921 than during the preceding or fol¬ lowing year, an increase particularly noticeable in the case of the late- maturing tail-grasses (table 6). There was a pronounced decrease in the height of all three species from Lincoln westward, the plants at Burlington averaging less than half as tall as at Lincoln. With respect to weight, the differences were even greater, oats and wheat yielding a third as much as at Lincoln. The average pro¬ duction for the three crops was 2,234 at Lincoln, 1,164 at Phillipsburg, and 882 at Burlington, in close correspondence with rainfall, evaporation, and chresard (table 7). Results in Grazing Exclosures. Experimental exclosures were installed in three representative areas of northern Arizona in 1918 in cooperation with the Biological Survey of the United States Department of Agriculture (Taylor and Loftfield, 1922, 1923). While these were designed to serve several purposes, the most important was to evaluate the role of grazing in the structure and yield of grassland and to determine the effect of the food-habits of the prairie-dog of the region (Cynomys gunnisoni zuniensis ) upon the carrying capacity and composition of the range. The latter is a portion of the mixed-prairie association, usually modified in this region by the suppression of the tall- CLIP-QUADRAT PHYTOMETERS. 87 grasses through overgrazing. The northern area lies in Coconino Wash, about 9 miles south of the Grand Canyon, and consists of Agropyrum glaucum and Sporobolus cryptandrus, with small amounts of Bouteloua gracilis, Stipa comata, and other grasses. The exclosure consists of two equal parts, proof against both cattle and rodents, but with one containing a group of prairie-dogs, and it lies beside an unfenced area provided with quadrats also. This series has permitted a quantitative study of the vege¬ tation under three conditions: (1) under total protection, (2) grazed by Table 7. —Growth and yield of crop-quadrats , 1923. Crop and station. Date of harvest. Height. Weight. Oats: in. gm. Lincoln. July 7 42 2,637.0 Phillipsburg. July 3 32 905.0 Burlington. July 7 18 806.5 Wheat: Lincoln. July 7 42 2,395.0 Phillipsburg. July 3 29 1,296.0 Burlington.. July 7 24 801.5 Barley: Lincoln. July 2 43 1,671.5 Phillipsburg. . .'.. July 3 37 1,292.5 Burlington. July 7 26 1,038.5 cattle alone, and (3) grazed by a known number of prairie-dogs. Similar exclosures are located at Williams and at Seligman, the former in a com¬ munity of Bouteloua gracilis and Muhlenbergia gracillima, the latter in one of B. gracilis and eriopoda. Table 8. Agropyrum glaucum. Sporobolus cryptandrus. Total quantity of grass. 1919. 1920. 1921. 1919. 1920. 1921. 1919. 1920. 1921. Total protection 100.0 117.1 138.8 164.6 32.8 81.9 264.6 149.9 220.7 Rodent grazing. Cattle and ro- 36.8 24.3 22.6 Trace. None. None. 36.8 24.3 22.6 dent grazing.. . 6.6 8.7 6.7 4.6 None. 6.4 11.2 8.7 13.1 The growth of the grasses under the three conditions has been measured by means of clip-quadrats, and at the Coconino station has yielded the figures presented in table 8, expressed as grams of forage per square meter: Agropyrum glaucum shows a consistent increase for the three years of total protection, probably owing to its better utilization of rainfall as a result of its sod habit (plate 11a). As a bunch-grass, Sporobolus cryp¬ tandrus appears to be more dependent upon the seasonal distribution of the rainfall, and it is also unable to hold its own in competition with the increas¬ ing Agropyrum. Rodents are especially fond of it, as are cattle also; but while the latter merely graze it to the ground, the prairie-dogs destroy it completely by the second year. 88 RELATED APPLICATIONS. TRANSPLANT PHYTOMETERS. Species Phytometers. As the basic method in the ecological organization of the field of experi¬ mental evolution (Clements and Hall, 1918-1923; Clements and Clements, 1923) and in the development of the new field of experimental vegetation (Clements and Weaver, 1918-1923, 1924), transplant gardens and areas have been installed in a number of climatic and edaphic series in the West. The climatic transect in the grassland extends from Nebraska City in the subclimax prairie with a rainfall of 33 inches, to Lincoln in the true prairie with 28 inches, Phillipsburg in mixed prairie with 23 inches, and Burlington and Colorado Springs in varying types of mixed prairie and short-grass plains with a rainfall of 17 and 15 inches respectively. The edaphic tran¬ sect at Lincoln runs through swamp, salt-flat, low prairie, high prairie, and gravel-knoll in the true-prairie climax and climate. The Petran transect at Pike’s Peak extends from mixed prairie with a 15-inch rainfall at Colorado Springs through successive zones of montane, subalpine, and alpine climaxes to a rainfall of 30 inches on the summit of the Peak, while the Sierran transect reaches from the Pacific Ocean to the summit of the Sierra Nevada and the sagebrush desert of the Great Basin. Edaphic transects have also been installed in various climates in these two major climatic series, but have been especially developed at the Alpine Laboratory and at Mather in the Hetch-Hetchy Valley. In addition to these, adapta¬ tion or ecad sequences of flowering plants have been developed in varying amounts of water-content or light, and similar sequences have been estab¬ lished for fungi and lichens, mosses, etc. Practically all transplant installations have been designed to serve a dual purpose, namely, plant response and factor measurement. In the mountain transects, evolution has so far been the primary objective and habitat analysis the secondary, while in the grassland series measurement of climate and climax has been paramount and adaptation secondary. However, both have been constantly kept in mind as reciprocals in the com¬ plete synthesis of plant and habitat. While these are an intrinsic part of the comprehensive phytometer method, the detailed account is necessarily left for the respective treatments (cf. Clements and Weaver, 1924). Community Phytometers. The development of community transplants as phytometers has neces¬ sarily been slower, because of the difficulties involved, especially those of transportation. These are most readily solved in the case of sod-cores or blocks, but the latter are too small for many of the phytometric values cnncrht. In the case of exclosures and inclosures, community phytometers of practically any desired size are possible, but these are limited to measure¬ ments of the effect of grazing or other animals (plate 11b). A further type of community phytometer with essentially the value of transplanting is obtained by modifying the holard through irrigating, flooding, or draining, or changing the light intensity by thinning, clearing, or producing an artificial canopy or shade. In practice, however, community phytometers have been confined largely to grassland and to lichens and mosses. In the RESUME. 89 case of the latter, entire communities are moved with the greatest readiness, but with sod or turf only fragments can be transported as a rule. The most feasible method of doing this is to cut a meter quadrat into four parts, which are then readily moved if the soil-blocks are not too thick. Areas several meters square have been transferred in this way from the alpine meadow to the montane climax. The simplest and most successful device for transplanting a community has been that of the reciprocal transplant quadrat, in which the central portions of two permanent quadrats are interchanged (Clements and Loftfield, 1923). In addition to the experimental transfers employed as phytometers are the large number of natural communities of definite limits, which occur as pioneers or relicts. These have the advantage of requiring no installation, but they are correspondingly less amenable to control. Their utilization as definite experiments under instrumental conditions has just been begun and the range of their usefulness is yet to be determined. RESUM E. Values and Limitations of the Phytometer Method. The six years of experience with the phytometer method in a wide variety of forms and applications seem to justify the conclusion that it is indis¬ pensable to all quantitative studies. Its sole limitation is the labor and expense involved, and this applies only to growth phytometers carried out on a large scale for the entire season. Even with these, when growth is expressed in yield or dry weight for the whole season, the operation is within the capacity of a single investigator, and this is still truer of short-period phytometers utilizing a simple function, such as transpiration. Moreover, it is an advantage rather than a limitation that phytometric studies must be carried through several seasons to obtain representative results, in so far as climate is concerned, a fact that applies with equal force to instrumental measurements as well. This is true also of edaphic applications, since local habitats vary with the seasonal swing. In spite of this, installations of phytometers for a single season have a wide range of usefulness whenever comparative values are sought independently of the annual variations. While the best use of phytometers is in conjunction with instruments, they render recording instruments necessary only in the more extensive instal¬ lations. In fact, it is to be expected that the increasing standardization of phytometers will cause them to largely replace the less satisfactory instru¬ ments, such as the atmometer in its various forms. It seems unnecessary to recapitulate the many uses of the various kinds of phytometers, but it is desirable to emphasize the leading role played by the phytometer in the exact analysis of the processes and changes of vegetation and crops. The plant or community alone can measure the factor-complex, as well as the efficient factors in it and the effect of their annual fluctuation. They are the only measures of the decisive part played by competition, and of the far-reaching effect of animal reactions upon vegetation. Finally, it is only by the exact evaluation of the control exerted by factor, competition, and animals that it becomes possible to distinguish present and past effects in vegetation. TABLES. Table 9. —Results from sealed phytometers, 1918. First Series. Ave. water re¬ quirement. Rel. water require¬ ment. Leaf area, sq. dm. Transpiration per sq. dm. Ave. transpiration per sq. dm. Rel. transpiration per sq. dm. Relative dry weight. gm. 2.35 2.65 2.89 2.73 2.31 2.89 2.89 2.74 2.71 7.43 8.84 gm. 396.6 363 353.6 390.7 215.2 279.8 283.7 260.9 281.9 408.2 238.6 gm. 518 100 376 100 100 370 71 264.3 70 101 542 365 765 100 67 100 408.2 238.6 100 58 100 103 100 65 509 66 766 100 100 91 657 86 Station. Plains Do. . Do. . Do. . Montane. Do. . Do. . Do. . Do. . Plains Montane. Plains.... Do. . Montane. Do. . Do. . Do. . Do. . Plains Montane. Do. . Species. Sunflower. ... Do. . . .. . Do. . . ... Do. . . ... Do. . . ... Do. . . .. .Do. . . .... Do. . . . .. .Do. . . Beans... . ... .Do. . . Oats. ... .Do. . . .... Do. . . ... .Do. . . .... Do. . . .... Do. . . . .. .Do. . . Wheat. . . .... Do. . . .... Do. . . CO cS oq 6 Z 1 1 1 1 1 1 1 1 1 6 6 6 4 8 4 6 6 4 5 4 10 "O © O gm. 932 962 1,022 1,066.5 497 808.6 820 714.8 764 3,033 2,109 384 367 218 104 177 281.5 130.5 295 210.7 384.5 xi • ^ © * b gm. 1.673 1.930 2.185 1.947 1.324 2.103 2.234 1.966 2.132 5.593 5.776 .530 .452 .456 .225 .286 .515 .296 .385 .276 .699 i © .« P c © i ■* *2 u p © © * B £ gm. 557 498 468 548 375 384 367 364 358 542 365 725 812 478 462 441 Second Series. Plains.... Do. . Montane. Do. . Plains.... Do. . Montane. Do. . Plains Do. . Montane. Do. . Plains Montane. Do. . Do. . Sunflower .. .Do. . ... Do. . .. .Do. . Oats.... .. .Do. . ... Do. . . .. . Do. . Wheat. . ... Do. . . ...Do. . ... .Do. . Sweet clover. ....Do. . ....Do. . . ... Do. . 1 1 1 1 20 13 27 26 9 14 23 20 5 4 5 3 gm. 4,124 4,018 2,468 2,432 1,677 1,012 1,512 1,312 1,014 784 1,537 1,190 510 5 .5 .5 .5 130.5 175 239 gm. 10.873 10.439 8.273 8.988 3.533 1.699 5.283 3.417 1.753 1.900 4.672 3.842 .965 .511 .590 .684 gm. 379 384 298 271 475 596 286 384 578 394 329 310 529 255 297 349 gm. 382 100 285 74 536 100 335 63 486 100 320 66 529 100 . 300 57 7.70 8.37 9.90 9.56 5.85 2.26 10.69 7.19 1.95 2.97 7.25 6.53 gm. 535.6 480 249.3 254.4 286.7 447.8 141.5 182.5 520 251.9 212.1 182.3 gm. 507.8 100 100 251.9 50 81 100 367.3 100 162 44 166 100 386 100 197.2 51 230 100 62 90 TABLES 91 Table 9. —Results from sealed phytometers, 1918 —Continued. Third Series. Station. Species. No. stalks. Total water used. Dry weight. Water require¬ ment. Ave. water re¬ quirement. Rel. water require¬ ment. Leaf-area, sq. dm. Transpiration per sq. dm. Ave. transpiration per sq. dm. ! Rel. transpiration per sq. dm. Relative dry weight. gm. gm. gm. gm. gm. gm. Plains. Sunflower.. 1 1 873 1 734 1,080 1 98 946 Do. . . . .... Do.... 1 1 869 1 557 1 200 1,140 100 1 88 994 1 970.1 100 100 Montane. . . 1 935 5 2 654 352 3 16 296 Do. . . . .... Do.... 1 954 2 3 037 314 3 07 310.8 Do.... . . . .Do. . . . 1 811 2 1 806 449 372 33 2 52 321 9 309.6 32 152 Gravel-slide. 1 709 1 496 474 2 64 268.6 Do. . . . .. . .Do. . . . 1 1 170 2.393 489 3 35 349.3 Do. . . . .... Do.... 1 978 1 945 503 489 43 2 84 344.4 320.8 33 118 Douglas fir.. 1 74 306 242 62 119.4 Do. . . . 1 110 .318 346 74 148.6 Do.... _Do_ 1 115 307 375 321 28 73 157.5 141 8 15 19 Spruce. 1 164 .419 391 72 227.8 Do. . . . .... Do.... 1 74 5 309 241 316 27 67 111 2 169.5 17 22 Plains. Oats. 6 885 953 929 1 57 563 7 Do. . . . .... Do.... 6 1,174 1 370 857 893 100 2 57 456 8 510.3 100 100 Montane. . . ... .Do. . . . 6 501.1 .840 597 1 31 382.5 Do. . . . .... Do.... 6 500 2 1 057 473 535 60 1 74 287 5 335 66 82 Gravel-slide. 5 412.5 .843 489 1 24 332.7 Do. . . . ... .Do. . . . 4 360.5 .527 684 1 01 356.9 Do. . . . .... Do.... 4 431 2 .781 552 575 64 9 479 1 389.6 76 62 Douglas fir.. 3 20.2 .102 198 16 33.6 Do. . . . _Do_ 4 23 .203 113 156 17 1.00 23 28.3 6 13 Spruce. .... Do.... 4 85 271 314 1 24 68.5 Do.... .... Do. . . . 3 60.4 .185 326 320 36 87 69.4 69 14 20 Plains. Rubus.... 1 721 1.91 377.5 Do. . . . .... Do.... 1 856.5 1.78 481.2 Do. . . . .... Do. . . . 1 863.5 2.51 344 400.9 100 Montane. . . . .. .Do. . . . 1 252.5 1.09 231.7 Do. . . . .... Do. . . . 1 295.8 1.18 250.7 Do.... .... Do. . . . 1 152.5 .73 208.9 230.4 57 Gravel-slide. 1 318 1.29 246.5 Do. . . . .... Do. . . . 1 259.5 .75 346 Do.... .... Do. . . . 1 83 .54 153.7 248.7 62 Douglas fir.. .... Do. . . . 1 33 .80 41.3 Do. . . . .... Do. . . . 1 96.5 1.02 94.6 Do. . . . .... Do. . . . 1 45 .77 58.4 64.8 16 .... Spruce. .... Do. . .. 1 46 .42 109.5 , ( . Do.... .... Do. . . . 1 63.7 .69 92.3 Do. . . . .... Do. . . . 1 50.5 .50 90.2 97.3 24 Table 10 .—Summary of sealed j)hytometers, 1918. 92 THE PHYTOMETER METHOD. • ® ° «? £ NOiOiONSNNNCCM CMCM-tf-^eocoooooeocMCM NNNNNNN*0 | 0NNO‘0(N(NNMN cocococococococmcmcoco^^cococococo T3 o • Pi >1 © O O CM : co o CM • CO o CM CM H H CM • rH rH CM • H rH CM • CM >>>>>> . db >> >> ; db >3 . >s 3 3 3 d 3 d • d 33 d • d >“9 >~3 >“S . <5 •< o o o • r> o o • n O o • o -H H-> • • • CO T*H T*< o o c c c c Q c o o iO rH o o c c c c iO r-f C o rH o t> © © © G C Q Q Q © Q Q Q © Q Q Q Q Q © Q © Q © d d d • • d d r*i • d d • d d d d d • d d • d d d • d >“S C-5 H-j . ♦“D . ►"5 . . . ►"D *"3 co 60 d <1 o o o o o QQQQ d *-5 © pH I c3 (-1 • rH a 03 d c3 ►H ^ © Q ft a *d d • o cr ©OOOOCMCO*Ot^O ONOiOOWMHHO co lO O^OCtDtD't OifOQN «-t O o o O CM CO O »C CD H N i o3 m • , © q ® ft a | ^ go <* etO^XNOOHiMOOOOi ENOOiONHNrfNOM a mC5iONOCCCMHHTj((N MNOiOOQO® CO CO H CC ® (N CD co *h >o co co CO b- oo ca CO r-t HO®»ON O C3 M' CO 03 ^ CM CM 03 «JL > C3 ® G8 ^COHNCOCOCN’fOOTfiN r «C0l>OI>0Ci0303l>l>iM'^ lO ^ 1 C »£> Tj< l> o CDOOiO eHNOCOO^NCOOH^OcOOCOCOOSCONiOCMCOiOOOCMCMO ^lOCOmCMiHCO^COMiOCONiOiOCOOOiOiOHCONCOTHCOiOCO +3 £ «) T3 03 £ s Os TtdMCDHC003i0O^CMC000rH03^TjC003CTjci0NO03 00 C003 COiOiOCOrtCOS^HCOCOCOOSCOiOCOOiOCO^CONNlOOO)^ 05 05 CO CD CO 05 CO CO 05 05 O O *"H rH rH rH rH O O O O *“H -H r-H r-H rH r-H O GO *"H Cl r-H QQ 6^ Z $ 33 -tfiOCMCMCMCOCOCOCMCOCOOOOCOCOCMCM »—i CM CO *0 i—l tH CO N N lOHCOCOtOCMCOCOCO rH CM ^ 1-1 co • ® O -u £ O ^ ft ■^lOCMCMCMCOCOCOCMCOCOCMiOCMCMCMCMCOCMCMHCMCMCMrHCOCOCOCO CO 33 03 • r- t- 03 in Hr-tC'lCMCOCOCOCOCOHrHHHCMCMCOCOCOCOCOHHCMCMCMCMCOCOCO CO 33 © • rH © © ft in u © p£ oOOOOOOOO cCQQQQQQPQ c d m Sh © > o O ’OOOOOOOO QmQQQQQQQQ -M 03 O O QQ o Q m d -Q d Ph o o o o QQQQ d o • i-i H-a cC CO ■o n ©'t 3 ® • © • © • © -=$ _ • o • o ■ q f ® .3 c.h si fl c q "S) I S © d csj © d © 03 ^ ^ TABLES 93 Table 11. —Results from unsealed phytometers, 1918. Second Series. Station. Species. No. of pots. No. of plants. Leaf- area. Dry weight. Ave. leaf-area. Ave. dry weight. Rel. dry weight. sq. dm. sq. dm. gm. Plains. Sunflower.. . . 3 3 6.25 7.573 2.08 2.524 Montane. _Do. 2 2 5.51 5.674 2.76 2.837 81 Plains. Beans. 5 5 9.29 4.898 1.86 .98 Montane. _Do.. 4 4 4.27 2.455 1.07 .61 62 Plains. Oats. 5 48 7.477 . 156 Montane. _Do. 6 40 5.468 .137 88 Plains. Wheat. 3 44 9.361 .213 Montane. _Do. 3 36 4.134 .115 54 Third Series. sq. dm. sq. dm. gm. Plains. Sunflower.. . . 5 5 12.09 9.274 2.42 1.855 100 Montane. _Do. 5 5 12.29 8.610 2.46 1.722 93 Gravel-slide.. . . _Do. 5 5 6.87 4.440 1.37 .888 48 Douglas fir... . _Do. 2 2 1.29 .240 .65 .120 7 Spruee. _Do. 3 3 .86 .475 .29 .158 9 Plains . Oats. 5 93 9.277 .100 100 Mnn tane. _Do. 5 82 10.806 .132 132 Gravel-slide. . . _Do. 5 74 8.690 .117 117 Douglas fir . . . _Do. 5 90 3.742 .042 42 Snrnee _Do. 5 79 4.364 .055 55 Table 12. —Summary of unsealed phytometers, 1918. Station. Species. Series. No. of pots. No. of stalks. Ave. dry weight. Ave. leaf- area. r Period. No. days. gm. sq. dm. Plains . Sunflower.. 2 3 3 2.524 2.08 June 12 to July 22 40 IVTnnt.ane . Do. . . . 2 2 2 2.837 2.76 .... Do . 40 Plains. .... Do.... 3 5 5 1.855 2.42 July 10 to Aug. 16 35 \Tnntane Do . . 3 5 5 1.722 2.46 _Do. 35 Grn vel-slide Do . . . 3 5 5 .888 1.37 _Do . 35 Dmi crl a .a fir. Do. . . 3 2 2 .120 .65 . . . .Do . 35 Snrnee _Do. . . . 3 3 3 .158 .29 . . . .Do . 35 Plains Oats. 2 5 48 .556 June 24 to July 22 28 Do 2 6 40 .137 _Do.'_ 28 PI a i n s _ Do... . 3 5 93 .100 July 10 to Aug. 16 35 Do 3 5 82 . 132 . . . ~Do. 35 Do 3 5 74 .117 _Do. 35 Dmi0*1 ns fir Do 3 5 90 .042 _Do. 35 £srkrnr*p* Do 3 5 79 .055 _Do. 35 Plains Beans. 2 5 5 .980 1.86 June 24 to July 22 28 M nn t.a n e Do. 2 4 4 .610 1.07 ... .Do.. . 28 Wheat 2 3 44 .213 _Do. 28 Do 2 3 36 .115 .... Do. 28 94 THE PHYTOMETER METHOD Table 13. —Results from sealed phytometers , 1919. First Series. Station. Species. No. of pots. Ave. dry weight, per plant. Ave. water re¬ quirement. Rel. water re¬ quirement. Ave. leaf-area. Ave. transpira¬ tion per sq. dm. Rel. transpira¬ tion per sq.dm. Period. Days. gm. gm. sq.dm. gm. Plains.... Sunflower 5 12.653 401 100 7.883 644 100 June 24 to Aug. 1 38 Do. . . Wheat. . . 5 1.606 557 100 2.146 384 100 .... Do. 38 Do. . . Oats. 3 1.252 567 100 2.008 354 100 _Do. 38 Do. . . Beans.... 5 5.803 665 100 8.977 430 100 June 26 to Aug. 1 36 Montane. Sunflower 5 6.444 352 87 5.330 420 65 June 27 to Aug. 1 35 Do. . . Wheat. . . 5 2.573 351 68 3.981 226 58 June 24 to Aug. 1 38 Do. . . Oats. 5 1.724 342 59 3.660 158 44 .... Do. 38 Do. . . Beans.... 5 2.623 424 63 4.429 251 58 June 26 to Aug. 1 36 Subalpine Sunflower 5 2.967 280 72 3.741 230 35 June 25 to Aug. 1 37 Do. . . Wheat. . . 3 1.764 173 26 3.07 78 20 .... Do. 37 Do. . . Oats. 3 1.632 249 43 3.041 133 37 .... Do. 37 Do. . . Beans.... 4 .822 287 47 1.061 245 56 . .. .Do. 37 Second Series. gm. gm. sq.dm. gm. Plains.... Sunflower 2 5.806 669 100 4.724 822 100 Aug. 5 to Sept. 8 34 Do. . . Wheat. . . 2 .482 977 100 1.023 460 100 Aug. 14 to Sept. 8 25 Do. . . .... Do. . . 2 1.128 858 100 3.517 218 100 Aug. 5 to Sept. 8 34 Do. . . Oats. 3 1.739 778 100 3.538 382 100 Aug. 7 to Sept. 8 32 Montane. Sunflower 3 2.107 592 88 2.207 565 69 Aug. 6 to Sept. 8 33 Do. . . Wheat. . . 3 .116 931 95 .240 450 98 .... Do. 33 Do. . . .... Do. . . 2 .542 644 75 .893 390 179 .... Do. 33 Do. . . Oats. 3 1.463 1,075 138 3.480 452 118 Aug. 8 to Sept. 8 31 Subalpine Sunflower 3 2.177 513 77 2.762 404 49 Aug. 4 to Sept. 8 35 Do. . . Wheat. . . 3 .628 622 63 1.091 358 77 . . . .Do. 35 Do. . . _Do. . . 2 1.293 594 69 2.331 329 150 Aug. 11 to Sept. 8 28 Do. . . Oats. 3 .692 609 78 1.359 310 81 Aug. 9 to Sept. 8 36 Table 14. —Results from sealed phytometers, 1920. Station. First series. Second series. Species. Aver. total transpira¬ tion. Aver. dry weight. Aver. water require¬ ment. Aver. total transpira¬ tion. Aver. dry weight Aver. water require¬ ment. Plains. Montane... . Subalpine. . . Plains. Montane.... Subalpine. . . Plains. Montane.... Subalpine. . . Sunflower... . . . . .Do. . . . .Do. Wheat. . . . .Do. . . . .Do. Oats. ... .Do. . . . .Do. gm. 1,734 1,311 359 1,050 740 408 1,529 965 497 gm. 3.8045 3.1582 .829 1.604 1.3943 .7541 2.7186 1.8082 .954 gm. 456.30 415.07 434.29 650.99 530.70 543.35 543.35 532.41 520.96 gm. 2,967 5,180 1,465.9 145.2 1,108.7 703.4 2,356.6 1,759.5 566.8 gm. 6.7879 14.5083 3.7213 .3151 2.5341 2.0122 5.4923 4.3182 1.2892 gm. 437.10 357.04 396.60 460.8 437.51 349.56 429.07 407.46 133.74 TABLES 95 Table 15 .—Average stem length and width of sunflowers in millimeters , 1920. First Series. Station. June 14 to 21. June 21 to 28. June 28 to July 5. July 5 to 12. July 12 to 19. Plains. 42.6 63.8 123.2 191 285.4 Montane. 16.4 32.2 74.4 132 212 Subalpine. 14 14.8 42.6 62.8 93 Plains. 2.88 3.12 4.26 5.54 6.80 Montane . 2.42 2.50 3.68 5.56 7.20 Subalpine. 2.55 2.57 3.34 4.18 5.40 Second Series. July July 26 to Aug. Aug. Aug. Aug. Old/llUlL 19 to 26. Aug 2. 2 to 9. 9 to 16. 16 to 23. 23 to 30. Plains. 16.8 38.8 57.2 87.2 166.8 287.4 Montane. 17.6 31.6 67.6 115.4 171.8 243.6 Subalpine. 17.6 20.6 35.4 58 75.2 107.6 Plains.. 1.76 2.04 2.72 3.2 4.14 4.94 Montane. 2.. 24 2.50 3.42 4.62 5.82 7.04 Subalpine. 2.46 2.38 2.74 3.52 4.12 5.02 96 THE PHYTOMETER METHOD Table 16. —Average daily transpiration of sunflower phytometers, 1923. First Series. June 13 to 18. June 18 to 25. June 25 to July 1. July 1 to 3. July 3 to 5. July 5 to 7. July 7 to 9. July 9 to 12. July 12 to 14. Sun Station: Average daily water- loss (c. c.). 16.2 32.37 32 48 31 00 67 50 85 00 90 00 47.90 85.90 Average leaf-area (sq. dm.). 0 627 0.871 1 511 1 908 2 342 2 777 2 994 3 628 3.959 Transpiration per sq. dm. 25.8 37.16 21 49 16.24 28.82 30 60 30.06 13.20 21.69 Half-shade station: Average daily water- loss (c. c.). 8 2 14 7 11 3 21 0 23 8 33 0 44 0 36 2 42 6 Average leaf-area (sq. dm.). 0.835 1.026 1 497 1 778 2 092 2.395 2.604 2.872 3.088 Transpiration per sq. dm. 9 81 14 32 7 54 11 86 11 37 15 77 16 89 12.60 13.79 Shade station: Average daily water loss (c. c.). 14.8 9.95 9 15 10 0 14 3 20 5 12 8 8.98 8.10 Average leaf-area (sq. dm.). 0.792 0.872 0.999 1 047 1 114 1.181 1.248 1.302 1.327 Transpiration per sq. dm.* . 20.87 11.39 9.15 9.55 12.83 17.36 10.26 6.89 6.10 Second Series. Aug. ' 2 to 6. Aug. 6 to 13. Aug. 13 to 20. Aug. 20 to 27. Aug. 27 to Sept. 3. Sun station: Average daily water-loss (c. c.). . . 3.97 3.60 2.58 6.20 4.96 Average leaf-area (sq. dm.). 34.22 42.17 55.92 65.56 78.05 Transpiration per sq. dm. 11.60 8.53 4.61 9.45 6.11 Half-shade station: Average daily water-loss (c. c.). . . 1.60 3.00 1.50 2.80 1.32 Average leaf-area (sq. dm.). 35.24 41.04 51.84 53.99 49.72 Transpiration per sq. dm. 4.54 7.30 2.89 5.18 2.65 Shade station: Average daily water-loss (c. c.). . . 0.47 0.91 0.50 0.53 0.40 Average leaf-area (sq. dm.). 31.64 36.94 44.96 50.82 51.68 Transpiration per sq. dm. 1.48 2.47 1.11 1.04 0.77 TABLES 97 Table 17 .—Growth of sunflower phytometers, 1923. First Series. j Date. Sun station. Half-shade station. Shade station. Phyto¬ meters. Checks. Phyto¬ meters. Checks. Phyto- meters. Checks. Average leaf-area in sq. cm.: June 18. 62.70 83.56 79.20 June 25. 111.55 100.68 121.71 104.08 95.22 77.87 July 2. 190.82 174.26 177.82 134.06 104.71 81.28 July 9. 342.99 274.20 128.25 July 13. 395.90 492.41 308.88 169.24 135.20 96.26 Average stem-length in mm.: June 18. 48.2 72.9 84 June 25. 82.7 119 165.2 178 181.5 187 July 2. 116 136 264.6 230 244.7 228 July 9. 180.5 393 338.1 July 13. 203.3 226 428.2 330 304.8 238 Average stem-diameter in mm.: June 18. 4 3.80 3.70 June 25. 3.90 4.30 4.20 4 3.65 3.70 July 2. 5.47 4.60 5.24 4.30 3.91 3.71 July 9. 6.54 6 09 4.02 July 13.. 7.45 6 6.64 4.40 4.27 3.70 Second Series. Average leaf-area in sq. cm.: Aug. 6. 34.22 38.05 35.24 40.19 31.64 31.37 Aug. 13. 50.13 46.82 46.84 51.79 42.24 38.86 Aug. 20. 61.72 55.51 56.85 63.03 47.69 45.72 Aug. 27.. 69.40 69.08 51.13 67.28 53.95 50.09 Sept. 3. 86.71 96.90 48.32 75.09 59.41 54.43 Average stem-length in mm.: Aug. 6. 88.9 112.8 97.8 128.2 110.2 118.3 Aug. 13. 105.5 130.5 125.5 165.5 156 160.5 Aug. 20. 117.5 146.2 145 203.5 180 195 Aug. 27. 145.5 137 162.1 234 200.6 214 Sept. 3. 155.5 183.5 169.2 250.5 213.7 257 Average stem-diameter in mm.: Aug. 6. 2.73 3.09 2.76 3.09 2.70 2.84 Aug. 13. 3.15 3.34 3.20 3.29 2.70 2.87 Aug. 20. 3.31 3.30 3.42 3.28 2.71 2.80 Aug. 27. 3.51 3.54 3.80 3.28 2.68 2.86 Sept. 3. 3.76 3.83 3.28 3.40 2.45 2.75 98 THE PHYTOMETER METHOD Table 18. —Dry weight and water requirement of sunflower phytometers, 1928. First Series. Station. Phytometers. Checks. Ave. water require¬ ment. Leaves. Stems. Roots. Plant. Leaves. Stems. Shoot. Average dry weight in grams: Sun. Half-shade. Shade. 1.2894 . 6233 .1650 0.6393 .7750 .1280 0.4769 .3352 .0614 2.4056 1.7335 .3544 0.8030 .3130 .1390 0.5500 .4040 .1106 1.353 .7170 .2496 804.9 486.5 124.91 Station. Leaves. Stems. Roots. Leaves. Stems. Percentage of sun-sta¬ tion values: Sun. Half-shade. Shade. 100 48.34 12.79 100 121.24 20.02 100 70.28 12.83 100 38.96 17.31 100 73.45 20.10 Second Series. Station. Phytometers. Checks. Ave. water require¬ ment. Leaves. Stems. Roots. Plant. Leaves. Stems. Shoot. Ave. dry weight in grams: Sun. Half-shade. Shade. 0.4589 .3402 .1695 0.3724 .3694 .1412 0.2047 .2789 .1024 1.0360 .9885 .4131 0.4792 .2142 .12778 0.3421 .1553 .1293 0.8213 .3695 .2571 165.1 94 58.7 Station. Leaves. Stems. Roots. Leaves. Stems. Percentage of sun-sta¬ tion values: Sun. Half-shade. Shade. 100 74.1 36.9 100 99.2 37.9 100 135.2 50.0 100 44.6 26.6 100 45.3 37.7 TABLES 99 Table 19. —Individual variability in transpiration of sunflowers. Fibst Series. (Disc. = Discarded) No. Loss in weight. Ave. leaf product. Loss per ave. product. No. Loss in weight. Ave. lead product. Loss per ave. leaf product. gm. gm. gm. gm. 1 12.6 2,570 0.0049 51 13.1 2,609 0.0050 2 10.5 2,556 .0041 52 7.9 1,263 .0062 3 11.5 2,328 .0049 53 8.4 1,274 .0065 4 10.4 2,773 .0037 54 Disc. 5 Disc. 55 13.5 2,877 .0046 6 14.7 2,575 .0057 56 Disc. 7 Disc. 57 6.9 2,952 .0023 8 Disc. 58 Disc. 9 21.8 3,451 .0063 59 11.7 2,430 .0047 10 Disc. 60 13.0 2,450 .0050 11 13.4 1,943 .0068 61 17.5 2,536 .0068 12 12.5 1,998 .0062 62 10.1 2,084 .0064 13 10.4 1,768 .0058 63 13.2 2,594 .0051 14 15.3 2,739 .0055 64 7.3 2,097 .0035 15 13.1 3,120 .0042 65 9.4 2,069 .0040 16 Disc. 66 14.0 2,916 .0048 17 Disc. 67 Disc. 18 Disc. 68 10.5 1,867 .0058 19 19.5 1,899 .0050 69 Disc. 20 Disc. 70 10.2 2,219 .0045 21 7.0 2,073 .0034 71 Disc. 22 13.7 2,053 .0067 72 Disc. 23 9.6 2,689 .0036 73 9.5 2,538 .0037 24 10.3 1,708 .0060 74 16.4 2,364 .0060 25 8.7 2,363 .0036 75 15.5 4,505 .0034 26 Disc. 76 16.9 3,636 .0048 27 10.8 2,474 .0044 77 15.0 3,109 .0048 28 18.0 3,010 .0061 78 10.4 3,088 .0034 29 Disc. 79 14.7 3,284 .0044 30 Disc. 80 10.4 2,993 .0031 31 14.3 2,495 .0056 81 14.6 3,313 .0044 32 15.0 2,527 .0059 82 8.1 3,137 .0026 33 10.1 2,469 .0041 83 9.8 2,834 .0035 34 16.4 2,599 .0063 84 14.7 3,604 .0041 35 11.1 2,036 .0055 85 7.5 2,609 .0029 36 7.6 2,188 .0035 86 15.5 3.254 .0051 37 4.8 2,292 .0021 87 Disc. 38 5.0 2,315 .0021 88 5.6 1,886 .0027 39 Disc. 89 Disc. 40 11.3 1,838 .0061 90 9.7 3,241 . .0029 41 8.6 2,869 .0030 91 Disc. 42 13.2 2,085 .0063 92 Disc. 43 5.0 1,643 .0030 93 6.8 2,471 .0028 44 10.1 2,219 .0046 94 6.0 1,579 .0038 45 10.0 2,224 .0044 95 9.9 2,821 .0035 46 Disc. 96 9.7 1,932 .0050 47 9.6 1,490 .0064 97 Disc. 48 9.4 1,679 .0056 98 17.1 3,513 .0049 49 11.8 2,200 .0053 99 20.7 3,762 .0055 50 7.7 1,887 .0040 100 Disc. 100 THE PHYTOMETER METHOD. Table 20 .—Individual variability in transpiration of sunflowers. Second Series. No. Loss. Leaf-area (sq. cm.). Loss per leaf-area. No. Loss. Leaf-area (sq. cm.). Loss per leaf-area. gm. gm. gm. gm. 1 19.0 30.38 0.65 60 24.0 40.78 0.58 2 20.7 31.04 .66 61 17.6 24.26 .71 3 20.8 30.39 .68 62 15.9 29.61 .53 4 18.2 24.42 .74 63 Disc. 5 19.6 33.24 .58 64 Disc. 6 18.7 30.41 .61 65 Disc. 7 15.7 28.75 .54 66 17.3 23.58 .73 8 17.0 31.08 .54 67 14.2 23.85 .59 9 33.7 52.16 .64 68 20.7 36.29 .54 10 19.0 40.84 .46 69 19.9 36.27 .52 11 16.4 27.99 .58 70 15.8 22.59 .69 12 12.4 26.03 .51 71 13.9 27.02 .51 13 15.6 30.74 .50 72 13.6 25.34 .53 14 18.3 42.42 .43 73 15.0 28.99 .51 15 Disc. 74 23.6 39.85 .59 16 6.9 33.50 .20 75 Disc. 17 14.5 36.61 .31 76 10.8 16.05 .67 18 24.0 46.55 .52 77 14.8 23.77 .62 19 19.0 28.23 .67 78 14.2 26.92 .52 20 15.9 26.29 .60 79 14.7 22.11 .66 21 17.1 24.06 .71 80 17.3 34.28 .54 22 27.2 38.39 .71 81 Disc. 23 15.9 26.58 .60 82 22.1 37.55 .59 24 14.0 26.29 .53 83 13.7 34.52 .39 25 23.5 33.69 .70 84 23.3 36.47 .63 26 14.5 23.59 .61 85 Disc. 27 14.2 28.26 .50 86 20.0 39.12 .51 28 17.3 28.67 .60 87 14.9 29.46 .50 29 15.3 29.69 .51 88 21.1 23.85 .89 30 13.2 23.74 .55 89 11.3 21.46 .52 31 18.2 28.64 .63 90 16.3 28.98 .56 32 29.4 52.55 .55 91 20.6 17.95 .59 33 19.7 26.83 .73 92 Disc. 34 27.1 61.02 .44 93 8.9 12.18 .73 35 11.0 24.87 .44 94 22.5 32.46 .69 36 17.1 29.04 .59 95 Disc. 37 18.4 35.11 .52 96 21.5 36.33 .59 38 13.3 16.92 .74 97 21.6 41.72 .51 39 12.7 23.70 .53 98 16.0 27.12 .59 • 40 16.0 24.95 .64 99 16.2 25.10 .64 41 Disc. 100 17.9 23.35 .76 42 33.5 42.78 .77 101 20.0 31.44 .63 43 23.9 40.00 .59 102 Disc. 44 17.4 39.20 .44 103 17.9 29.41 .60 45 Disc. 104 16.2 29.14 .55 46 17.9 33.09 .54 105 Disc. 47 23.6 36.63 .64 106 Disc. 48 Disc. 107 15.0 22.06 .67 49 14.7 23.05 .63 108 19.0 27.48 .69 50 15.8 24.25 .65 109 21.7 45.87 .49 51 10.3 17.61 .70 110 21.5 34.46 .62 52 17.2 28.38 .57 111 Disc. 53 14.7 21.28 .69 112 18.9 30.35 .62 54 14.2 22.46 .63 113 19.0 26.13 .67 55 12.4 23.24 .53 114 Disc. 56 13.7 25.12 .54 115 18.5 31.43 .58 57 10.7 22.24 .48 116 Disc. 58 9.8 20.90 .46 117 18.6 32.61 .57 59 Disc. 118 14.7 22.76 .69 TABLES 101 Table 21.— Short-period phytometers, sun and shade, September 16, 1923. Sun. Half-shade. Shade. Loss in weight, 11 a. m. to 4 p. m. Leaf product. Loss per leaf product (raised to whole numbers). Loss in weight, 11 a. m. to 4 p. m. Leaf product. Loss per leaf product (raised to whole numbers). Loss in weight, 11 a. m. to 4 p. m. Leaf product. Loss per leafproduct (raised to whole numbers). gm. gm. gm. 6.7 54,171 123 1.8 21,448 84 1.1 25,796 42 6.3 29,484 213 1.7 21,729 80 1.1 19,261 58 2.5 12,511 200 1.3 14,110 92 1.1 22,135 49 3.6 18,946 190 1.6 13,257 72 0.4 13,394 29 Average loss: Sun, 185; half-shade, 82; shade, 44.5; percentage of sun, 100, 44.3, 23.5. Table 22.— Short-period phytometers, sun and shade, September 18, 1923. Station. Sun. Half-shade. Shade. 9 to 11 a. m. 11 a. m. to l h 30 m p. m. l h 30 m to 3 p. m. 3 to 5^30™ p. m. Station. Leaf product. Loss. Hourly loss per leaf product. Loss. Hourly loss per leaf product. Loss. Hourly loss per leaf product. Loss. Hourly loss per leaf product. Sun. 29,484 gm. 9.0 1 177 gm. 6.2 84 gm. 3.4 74 gm. 2.5 33 Do. 54,171 8.2 75 9.2 67 4.3 52 2.4 17 Do. 18,946 12,511 21,448 7.1 187 3.1 65 2.1 74 1.4 29 Do. 5.4 211 2.6 83 2.1 111 .8 25 Half-shade. 3.2 74 1.6 29 1.2 37 .3 55 Do. 14,110 11,814 20,692 19,261 2.1 74 1.9 53 .5 23 .2 5 Do. 1.2 50 1.7 57 .3 16 .2 6 Do. 1.8 43 2.1 40 .8 25 .3 5 Shade. 1.8 46 .9 18 .5 15 .1 2 Do. 13,394 25,796 21,729 1.1 41 .6 17 .3 14 .1 2 Do. 2.7 52 1.8 27 .7 18 .2 3 Do. 2 46 1 18 .5 13 .2 3 Averages: Sun. 167 75 78 26 Half-shade. 60 45 25 18 Sha.de. 46 20 15 25 Average hourly standard evaporation. 9 to 11 a. m. c. c. 1.56 .71 .70 11 a. m. to l h 30“ p. m. c. c. 1.39 .71 .42 l h 30 m to 3 p. m. c. c. 1.95 .83 .46 3 to 5 h 30 m p. m. c. c. 1.14 .33 .27 Temperature. 9 a. m. ° C 2 39.0 37.0 38.5 11 a. m. °C. 15.2 7.0 9.2 2 p. m. °C. 11.0 12.0 10.5 3 h 30 m p. m. °C. 9.6 9.3 9.8 s^o™ p. m. °C. 4.2 3.8 5.3 1 Raised to whole numbers, as in all succeeding tables. 2 The 9 a. m. readings were made at soil surface, all others at 3 inches above soil surface in shade. 102 THE PHYTOMETER METHOD Table 23.— Short-period phytometers, surface and angle, September 20, 1923. Position. Leaf product. 9 to 11 a. m. 11 a. m. to l^O 111 p. m. l^O 111 to 3 h 30“ p. m. S^O 111 to 4 h 30 m p. m. Loss. Hourly- loss per leaf product. Loss. Hourly loss per leaf product. Loss. Hourly loss per leaf product. Loss. Hourly loss per leaf product. gm. gm. gm. gm. Level turf. 14,110 3.7 131 6.5 184 3.4 120 0.6 28 Do. 11,814 3.3 148 3.8 120 4.1 173 1.1 62 Do. 20,692 5.1 120 6.8 131 6.1 247 2.4 77 Level gravel. 12,969 3.3 127 3.6 111 2.7 104 1.3 66 Do. 12,511 4.8 192 4.6 147 4.5 180 2.1 112 Do. 18,946 3.5 92 3.5 74 2.5 71 1.1 48 Leaves horizontal. . 21,729 2.6 60 5.2 96 3.5 80 1 31 Do. 26,028 5.4 104 7.5 115 4.7 90 1.7 44 Do. 19,261 5.7 149 5.5 114 4.5 117 1.2 42 Leaves inclined.... 25,796 7.3 142 9.2 143 7.2 140 2.9 75 Do. 53,335 7.9 74 11.5 80 6.0 56 2.5 31 Do. 18,856 5.7 151 8.2 171 4.2 111 2.2 78 Averages: Level turf. 133 145 180 56 Level gravel .... 137 130 118 75 Leaves horizontal 104 108 96 39 Leaves inclined. . 116 131 102 61 Average hourly standard evaporation. Station. 9 to 11 a. m. 11 a. m. to 1*30“ p. m. l^O® to S^O 111 p. m. S^O 111 to 4 h 30 m p. m. Level gravel. c. c. 1.137 c. c. 2.520 c. c. 3.800 c. c. 3.50 Level turf. 1.820 2.240 2.970 1.575 Sloping gravel. 2.307 3.266 4.260 1.657 Temperature (° C.). Station. ll h 20 m a. m. 12 h 45 m p. m. 2 h 15 m p. m. 3 h 30 m p. m. Level gravel: 3 in. above surface (shade). 19 22.6 21.0 18.0 Soil surface. 32 38.0 31.8 25 8 Level turf: 3 in. above surface (shade). 18.6 21.2 20.6 16.0 Soil surface. 18.8 22.2 22.6 20.0 Gravel slope: 3 in. above surface (shade). 29.8 18.2 Soil surface. 45.8 38.0 TABLES 103 Table 24. — Short-period phytometers, variability, and sun and shade, September 21, 1928. Station. Sun. Half-shade. Shade. Leaf product. 9 h 40 m to 11^40™ a. m. Station. Loss. Hourly loss per leaf product. Sun. 14,110 gm. 3.8 135 Do. 20,692 7.5 181 Do. 12,511 4.8 112 Do. 18,946 3.6 95 Do. 19,261 6.9 178 Do. 25,796 8.5 165 Do. 21,448 4.6 107 Do. 21,729 4.6 106 Do. 26,028 5.1 98 Do. 53,335 8.6 81 Do. 11,814 5 212 Do. 12,969 4.1 157 Average, sun. . 135.5 Average hourly standard evaporation. 9 h 40 m to 11 a. m. c. c. 2.64 llMCP a. m. to 2 h 40 m p. m. c. c. 2.83 1.56 .84 11^40™ a. m. to 2 h 40 m a. m. Per¬ centage of sun. Station. Loss. Hourly loss per leaf product. gm. S Sun. 10.0 121 Do. 5.6 149 Do. 3.4 89 Half-shade. 2.3 40 Do. 5.1 66 Do. 2.2 34 Do. 3.3 51 Shade. 1.2 15 j Do. 1.7 11 Do. .4 11 Do. .3 7 Average: Sun. 119.6 100 Half-shade. 47.7 39 Shade. 11.0 9 Air-temperature, in shade 3 in. above soil surface (° C.). 12 h 50 m p. m. 20.8 18.2 12 3 p. m. 1 17 17 13.8 1 21.8° in sun. 104 THE PHYTOMETER METHOD Table 25. — Short-period phytometers , slope-exposure, September 26-27, 1923. 8 h 30 m to ll h 30 m a. m. ll h 45 m a. m. to 3 p. m. 3 to 6 p. m. 6 p. m. to 6 h 45 m a. m. Station. Leaf product. Loss. Hourly loss per leaf product. Loss. Hourly loss per leaf product. Loss. Hourly loss per leaf product. Loss. Hourly loss per leaf product. South. 34,688 23,747 gm. 10.8 104 gm. 8.1 72 gm. 1.7 16 gm. 0.8 2 Do. 8 112 5.3 66 1 14 1.1 3 Do. 36,627 13.1 119 10.1 85 1.9 17 .5 1 North. 35,175 12.2 116 15.5 136 3.8 36 3.5 7 Do. 27,616 44,779 9.7 105 10.1 113 3.6 43 2.3 6 Do. 12.2 90 x 9.8 76 4.8 40 1.8 3 Average: South. 112 108 40 5 North. 104 74 16 2 Average standard hourly evapora¬ tion: South. c. c. 2.75 c. c. 3.64 c. c. 3.25 c. c. 2.05 North. 1.60 3.01 2.52 1.32 Temperature, ° C. Stations. 8 h 40 m a. m. lO^O" 1 a. m. 12 m. 3 p. m. 6 p. m. e^o™ a. m. 20.4 22.2 25.1 21.8 13.6 6.4 11.4 18.6 19.8 21.3 13.4 6.2 South, North BIBLIOGRAPHY. Baker, F. S. 1916. Aspen as a temporary forest type. Jour. For., 16:294. Briggs, L. J., and H. L. Shantz. 1912. The wilting coefficient for different plants and its indirect determination. Bur. Plant. Ind. Bull. 230. - -. 1913. The water requirement of plants. Bur. Plant. Ind. Bull. 284. Clements, E. S. 1905. The relation of leaf structure to physical factors. Trans. Am. Mic. Soc., 26: 19. Clements, F. E. 1904. Development and structure of vegetation. Rep. Bot. Surv. Nebr., 7. -. 1905. Research methods in ecology. -. 1907. Causes of alpine dwarfing. Science, 25: 287. •-. 1907 a . Plant physiology and ecology. -. 1916. Plant succession. Carnegie Inst. Wash. Pub. No. 242. -. 1920. Plant indicators. Carnegie Inst. Wash. Pub. No. 290. -. 1921. Aeration and air-content. Carnegie Inst. Wash. Pub. No. 315. -and G. W. Goldsmith. 1919-1922. The phytometer method. Carnegie Inst. Wash. Year Books 18-21. -, -. 1923. The phytometer method. Carnegie Inst. Wash. Year Book 22:303. - and H. M. Hall. 1918. Reciprocal transplants. Carnegie Inst. Wash. Year Book 17: 292. -, -. 1919-1923. Experimental taxonomy. Carnegie Inst. Wash. Year Books 18-21. -- and J. V. G. Loftfield. 1923. Permanent quadrats and transects. Carnegie Inst. Wash. Year Book 22: 320. - and D. C. Lutjeharms. 1921-1922. Slope-exposure studies. Carnegie Inst. Wash. Year Book 20-21. —- and J. E. Weaver. 1918. The phytometer method. Carnegie Inst. Wash. Year Book 17: 288. -, -. 1924. Experimental vegetation. Carnegie Inst. Wash. Pub. No. 355. Crump, W. B. 1913. The coefficient of humidity: A new method of expressing the soil moisture. New Phyt., 12: 125. Gain, E. 1895. Action de l’eau du sol sur la vegetation. Rev. Gen. Bot., 7: 15. Hedgcock, G. G. 1902. The relation of the water-content of the soil to certain plants, principally mesophytes. Rep. Bot. Surv. Nebr., 6. Heinrich, H. 1874. Ueber das Vermogen der Pflanzen den Boden an Wasser zu erschopfen. Tagb. Naturf. Breslau, 1874. Hesselmann, H. 1904. Zur Kenntnis des Pflanzenlebens schwedischer Laubwiesens. Mitt. Bot. Inst. Univ. Stockholm. Hildebrandt, F. M. 1921. A physiological study of the climatic conditions of Mary¬ land, as measured by plant growth. Physiol. Res., 2: 341. , Hole, R. S. 1921. The regeneration of sal ( Shorea robusta ) forests. A study in economic oecology. Indian For. Rec., 8: 163. -and P. Singh. 1916. Oecology of sal ( Shorea robusta ) forests. A study in eco¬ nomic oecology. Indian For. Rec., 8: 163. Iljin, W. S. 1916. Relation of transpiration to assimilation in steppe plants. Jour. Ecol., 4: 65. Jean, F. C., and J. E. Weaver. 1923. Relation of holard to root development and yield. Carnegie Inst. Wash. Year Book 22:313. - -. 1924. Root behavior and crop yield under irrigation. Carnegie Inst. Wash. Pub. No. 357. Johnson, E. S. 1921. The seasonal march of the climatic conditions of a greenhouse, as related to plant growth. Md. Agr. Expt. Sta. Bull. 245; Mon. Weather Rev. 50: 197, 1922. Livingston, B. E., and F. T. McLean. 1916. A living climatological instrument. Science, 43: 362. Lutjeharms, D. C. 1924. Environmental differences on north and south slopes of a canyon, based upon measurements of climatic factors and plant growth. 105 106 THE PHYTOMETER METHOD. McLean, F. T. 1917. A preliminary study of climatic conditions in Maryland, as related to plant growth. Physiol. Res., 2: 129. McLean, R. C. 1919. Studies in the ecology of tropical rain-forest, with special reference to the forests of south Brazil. Jour. Ecol., 7: 5. Ridgway, C. S. 1918. A promising chemical photometer for plant physiological research. Plant World, 21: 234; Mon. Weather Rev., 46: 117. Sampson, A. W. 1919. Climate and plant growth in certain vegetative associations. U. S. Dept. Agr. Bull. 700. —-and L. M. Allen. 1909. Influence of physical factors on transpiration. Minn. Bot. Studies, 4: 33. Sachs, J. 1859. Ueber den Einfluss der chemischen und der physikalischen Beschaffen- heit des Bodens auf die Transpiration. Landw. Vers. Stat. 1. Taylor, W. P., and J. V. G. Loftfield. 1922-23. Destruction of the range by prairie- dogs. Carnegie Inst. Wash. Year Book 21: 353; 22:314. Weaver, J. E. 1924. Plant production as a measure of environment. Jour. Ecol. 12:205; cf. Carnegie Inst. Wash. Year Books 20:400, 22:312. - and J. W. Crist. 1924. Direct measurement of water-loss from vegetation without disturbing the normal structure of the soil. Ecology 5:153. -, F. C. Jean, and J. W. Crist. 1922. Development and activities of roots of crop plants. Carnegie Inst. Wash. Pub. No. 316. -and A. F. Thiel. 1917. Ecological studies in the tension zone between grass¬ land and woodland. Rep, Bot. Surv. Nebr., n. s., 1. CLEMENTS AND GOLDSMITH PLATE 2 A. Mixed prairie at plains station, 6,100 feet, Colorado Springs. B. Montane forest (Pseudotsuga mucronata) at montane station, 8,600 feet, Alpine Laboratory. CLEMENTS AND GOLDSMITH PLATE 3 A. Subalpine forest (Picea engelmanni ) at subalpine station, 10,800 feet, Pike’s Peak. B. Battery of large wheat phytometers, montane station, 1920. CLEMENTS AND GOLDSMITH PLATE 4 A. Battery of sunflower phytometers, plains station, 1918. B. Battery of sunflower phytometers, montane station, 1918. C. Battery of oat and wheat phytometers, montane station, 1918. CLEMENTS AND GOLDSMITH PLATE 5 • ■ - 7 ’ B. Half-shade station, 1923 A. Sun station, 1923 CLEMENTS AND GOLDSMITH PLATE 6 A. Full-shade station, 1923. B. Photosynthesis and respiration phytometers, sun station, 1923. CLEMENTS AND GOLDSMITH PLATE 7 A. Sunflower phytometers, sun station, first series, 1923. B. Same, half-shade station. C. Same, full-shade station. CLEMENTS AND GOLDSMITH PLATE 8 11 11 1 -&44I Jif m ill jl L,. i 1 Jii m /fl # M fpl a !J| l#A\ j§g§g§||f Wmm mbseM fm ABk.. flSSBS 17 33 A. Growth of shoots, shade, half-shade, and sun stations, second series, 1923. B. Growth of roots, sun, half-shade, and shade stations. CLEMENTS AND GOLDSMITH PLATE 9 A. Battery of sunflower phytometers, slope-exposure transect, mesocline station. B. Same, canyon-bottom station. C. Same, xerocline station. - CLEMENTS AND GOLDSMITH PLATE 10 A. Sod-core phytometers and details of installation, Burlington. Colorado. B. Clip-quadrat phytometer in Bulbilis-Bouteloua short-grass, Burlington. CLEMENTS AND GOLDSMITH PLATE 11 Total Protection Prairie Dog plot Cattle Grazed PLOT A. Agropyrum glaucum from clip-quadrats in cattle-prairiedog inclosure, cattle exclosure, and open range, Grand Canyon, Arizona. B. Cattle-rodent exclosure. Santa Rita Range Reserve. Tucson, Arizona, showing growth of desert-plains grassland under complete protection. DEPARTMENT 0> : ' lk - ' _ r r • i , ,K UW»* Y, STATE COILT-G' • ,-r ii it. M T . .. n l i i h w i f