The person charging this material is re- sponsible for its return to the library from I which it was withdrawn on or before the ; Latest Date stamped below.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. UNIVERSITY OF ILLINOIS LIBRARY AT URBANA-CHAMPAIGN BUILDING I L161 — 0-1096 GROWTH IN SEEDLINGS OF PHASEOLUS VUL- GARIS IN RELATION TO , RELATIVE HUMIDITY AND TEMPERATURE BY CECIL FREDERICK PATTERSON B. S. A. University of Toronto, 1918 M. S. University of Illinois, 1 920 THESIS Submitted in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY IN BOTANY IN THE GRADUATE SCHOOL OF THE UNIVERSITY OF ILLINOIS 1921 « « »•¥ "^■f-. 1®^ ‘'w • ■*^<"’ ■ •* k;- .-■^ . me^''’r- ■....' 'rare A^^vife.'--/ .’..I vi0j-44itA ! . >':>i«ii54a(;i'r' ,j - . ii ?r -'I 6 |B!( .*»tRaa? 0 vi-r»/* < • ‘■* •ffi.^ '^, - ; J ■ wvilu i 9 ,v jr^>3:^ udi ‘t*j\ oa3fl!4»tf-'.-> ■ 1 W 3j% Dj . .^- 5 -■■’ 'J -'■. V • * cn C#tl * . ■?. 1* j -4s i r « I <» UNIVERSITY OF ILLINOIS THE GRADUATE SCHOOL Ma y 9, I HEREBY RECOMMEND THAT THE THESIS PREPARED UNDER MY SUPERVISION BY Cecil Frederick Patterson F.NTTTT.RD G rowth in Seedl ii Relation to Relative Humidity aiid Temperature BE ACCEPTED AS FULFILLING THIS PART OF THE REQUIREMENTS FOR THE DEGREE OF Doctor of Philoaophy. In Charge of Thesis f Head of Department A Tr, Committee on Final Examination* ^Required for doctor’s degree but not for master’s Digitized by the Internet Archive in 2016 https://archive.org/details/growthinseedlingOOpatt TABLE OF CONTENTS. Page I , ACKNOWLEDGMENT II. INTRODUCTION 1 III. REVIEW OF LITERATURE 7 IV. MATERIALS AND METHODS 14 1. Apparatus 15 2. Preparation of Seedlings 18 V. OUTLINE OF EXPERIMENTS 24 VI. PRESENTATION OF DATA 26 1. Growth of Seedlings in Continuous Darkness 27 2. Growth of Seedlings in Darkness Alternating with Light 40 VII. DISCUSSION 46 VIII. SUMMARY 59 IX. CONCLUSIONS 61 X. LITERATURE CITED 62 XI. VITA 73 I. ACKNOWLEDGMENT. The work here reported was performed in the Laboratory of Plant Physiology, University of Illinois, under the direction of Prof. C. F. Hottes. The writer feels greatly indebted to Professor Hottes for suggesting the problem and for his ever- ready and continuous assistance in constructing and arranging the apparatus. His suggestions on methods of experimentation and on working up the data are fully appreciated, and only through his efforts and his encouragement, during the course of the investigation, has the material here presented been made available. **<.i V -I ( . * ' '*%-2 i- V ■■ V ' 'i..tK 'r>* i '' , ;,'■'/ -L»'- ■ '; . ' ’ ' a ■% " '#^*13 :fl y yV 4.'> r ' ■'■%•' ^Bi Ijr 'if ' ■, ■’ it - 1 - II. INTRODUCTION. It is an undisputed fact that environmental conditions play an important role in determining the rate of growth in plants. Agriculturists, horticulturists, and others interested in the growing of plants have observed that certain conditions of environment are favorable to growth, while other conditions are unfavorable and retard this fundamental life process. Dur- ing one season, plants of a given species thrive and produce vig- orous growth, while during the season following, on the same soil and under similar cultural conditions, the corresponding growth rate suffers a marked decrease. In a like manner/ growth during one period in the growing season may be more rapid by night than by day, while during another period, in the same sea- son, the reverse may be true. As to what factor or factors are responsible for the differences in the responses of plants to the physical environ- ment little is known. In the literature on plant physiology^ some of the differences in plant response have been attributed to variations in definite environmental factors with little or no experimental evidence to substantiate the conclusions drawn. Plant physiologists, plant ecologists and others, in studying growth, have noted differences in the behavior of plants grow- ing under different sets of conditions and, in many cases, have ascribed the differences in growth to a variation in one factor '■■•r ' ', •< , ®’ ’' '’ S ” E^f* n'- r J ' . ■ Si!-. ■ *_::.■ |!f; *si.’i: ^ ^ ., /^: ^ :^:^^ar ' .J ^ e- jaig'- 1 ', K> i-)«' Wii.-.t life ^^?h' i^a^fftiiji-^i .' ■'.X'V': V - "'i., - .:,it_ ' • ■ * , .'• r - •:'- .•y ■^v„ JKV *' '*r •■' ' "' ’ ^ ■-; ’ '.' ' *• • '■^ V' "' ' ^ ^ ' ■^'^ •"'” '■* ^ ^Wv‘.Sb^' *K . V ' ■ - '^-- ' ■' 'y'^ .* *"“■« '. -ip ^'.■ v>'^j iti^^^:^-^r.;*Se ,.f 1 ■ iV A-v. /". ■• i > '» ‘‘ . •' 1 ■ ' L-> *31.4.. ^ '’■ , Ti VI 6kei«! I... ’ , ■'•'*■ ■■•■'*' ^'V '.Vj>- »- . ^ ^ .’■'r^'Yf 4tr xjiJk a.riv’' ir£'.v-nv*"^ ’. ■' ■ ■• ■" o ■' ■■ ’ ■■- ^'.fe-^,i. / -■ '4 '■ii- • V . *. ■< ■".'j?'. 4TI‘ . .: ‘ ai. - 'atn^vrr 1 Kl^' 'v *'' '«■■■; ' ‘ ^'v. ^ 1 '" ‘ ' -■• . ■- -3- when the cause might reasonably be attributed to a variation in several factors. In such cases it was not realized that the changing of one environmental factor resulted in a changing of two or more factors. For instance, Reinke ('76), in early studies on plant growth, observed that a change from light to darkness was usually accompanied by an increase in the relative humidity. The conclusion of Brefeld ('77) that the formation of the pileus in Coprinus depended upon the presence of light was found to be in error. Lakon ('07) showed that excluding the light from the vessel in which the fungus was growing changed the temperature and the relative humidity of the atmosphere surrounding the fungus. Experience has shown that, in nature, light, temperature and relative humidity are closely interrelated and that the condition of one is dependent, in a marked degree, upon the condition of the other two. As the light decreases in intensity the temperature falls and reaches a minimum during the hours of darkness. With this fall in temperature an increase in the relative humidity follows. On the return of light the temperature rises and a fall in the relative humidity results. To these rapid and often wide changes little attention has been paid, by many workers in the field of plant physiology. From a study of the plant environmental complex, as a whole, it may be seen that, in growth studies, every factor must receive due consideration. Jost ('07) recognized that the daily periodicity in relative humidity, in temperature and in light, occurring in nature, act unequally and often antagonistically >. . . . Ij t 1 ^ ■* *, *V ^ •*•■ {'■'■'•■ 1. - ■ ■' I # . Vi . ■ f. -»v ' -- ,*-■ vst v8^ ’Jf, S»i f ■•*’ ^ Jl'^' '”* '■ .it^^ •. ' / ^■ a|o‘. Y#*" / ■ liLW^’’#ffci;' ■* I] • ■ Ww ‘■^ - ;■ r ^ w ^■Vt i » ” 'T^,' i^if » % y r ‘■^'^ • « ■ > . 1^ ■ *K .-^i . if}- . j. ■' V • V-'W *'■ * •i^Jlfc ... .... .tt '._.... . ... '..ll'^ -3- upon the growth processes* The same authority acknowledged that it was impossible to interpret growth responses as affected by three variables combined. High temperatures, during the day, may retard growth and during the night, when the temperature drops to near the optimum, the growth rate may increase. Like- wise^ conditions may exist where the converse is true. Still more complex is the problem when the relationship of soil temper- ature to these factors and to growth is considered. Free ('ll) maintains, "As a part of the surrounding temperature the temper- ature of the soil is scarcely less important than that of the air". On the other hand, Godlewski has shown that a drop in the soil temperature from 20.7 C. to 5.5 C. results in an insignifi- cant decrease in the growth rate of the shoot. MaoDougal ('03) has shown that the soil temperature, at the average depth for roots of herbaceous plants, reaches a maximum between 8 and 11 o'clock in the evening and a minimum between 8 and 10 o'clock in the forenoon. From this it is evident that when the atmospher- ic temperature is falling, during the early hours of the night, the relative hujjidity and the soil temperatures are rising, and v/hen the atmospheric temperature is rising, in the early part of the day, the relative humidity and the soil temperature are falling. In order to avoid making the errors so common in much of the experimental work in plant physiology, it is necessary to carry out experiments under conditions that are absolutely under the control of the operator. DeCandolle ('05) recognized the ’J ) - r r ;v -F • fpv ' ;'' -I USk^' j ' • ^ ' j ^ ^ V j* ' ( ' * tv ' ’" *” ' 1?^W^ I '"TM>n, Xi ■ ■■' •f;: •/ ill '4 - '.•% .vr ci'‘-^' tio'i^^* '^03 V. Vf.- , '• ■ ^ 'r- /." ' , ■ T'.'^ l'/;j ■' ' TOil.'XC 'r;^if^ & . $tf- 'ifjjii ^ ■Eif^o^fk'USh’ff [U ‘q(.' ,. *^- .- ;. '. ■'••'■■: ■'" ■ «■•• '»• . '■'j>> » • ■ *'' ' • •• ^ **/u ■ • ' * k • 'ilt‘'i .'' , ■.■^’'•ww , 1^»- '■ - fijVJ H'> ' •. SCI ti 4f%s^va^k4; J^.-lii »•(' ■■ ’• ' ■ *“•'.• •'■ '^'i»'-* *, ‘ *' ’-j'j • ' i'V '; -^‘i'' • , '■ '■ ( -.;, ■• "*'/■ • ''*' X*j>' ;'«* .;■ ' ' ,; , . i f ' .^. '■- :, 4 • ., W: -4- importance of controlled conditions in a study of plant growth, and in an address, cited by Abbe ( '05), emphaaized the need for plant houses in which the various environmental factors could be controlled and changed at will. This need received the endorse- ment of Abbe ('05)^ who recognized the limitations of correlating field observations on plant grovrbh with climatic data. In a re- cent work^ Livingston (*17) has sounded a note of warning to the investigator and has drawn attention to the fact that, for solv- ing the fundaiuental problems in growth, an environmental control apparatus is indispensable. Only recently has the dream of DeCandolle been realized. For some years^ chambers in which the light and atmospheric temperature factors could be maintained constant or changed as desired have been in existence; but where relative humidity plays a part in determining the growth response, the usefulness of such chambers is limited. In the plant chambers recently de- vised by Hottes ('21), the humidity factor also is under control. These chambers, which are sufficiently large to accomodate higher plants throughout their entire growing period, are so arranged that the light, temperature and moisture factors are under perfect control of the investigator. From a study of the methods of experimentation axiopted by the various investigators in this fieldjit may be seen that in many cases the conclusions reached are unwarranted. The in- crease in the rate of elongation in shoots of sunflower during darkness, obtained by Reinke ('76), may have been due to an in- ^P; ■ : ; :: ^lai ^..Q:f^x- -teiC U,'< \l4fh l . c^^.%■T^.{> . 1 ». V.. ”■■ ■' ■ jf;- ■ ■■ . ■ ' a ‘ y- • n ’i^Wi f 'V* i . k fc“ • IjH' ' Tu,-; V, ■ '• . • . fi . ' » ' ■-■' • • 'ft, i'" . . ■■)' . : ' ' ^ * i V- i^: n'i^.lc* u « sf 4 ,%i Jfe.. ^^^‘^V.. 0 ^’^* • • *- -•, ■ ' ‘ "* i . ^ '’v/ , '* \^t-. •••'>'!""' 5 Ittf riju*ih v.\. #'i ^ "v' 1 Ik:- ‘ t '’'-V "■■' ' ^‘'^<1 |f‘\~ 6 j:. v*\t, ,<»>! ^*i,rz0ipjcj€i^ 4 fi* >1 .f^O'tC -Sv>, H t 1 1' 'r ' / ; A:< iJ.tW , .U> 'T«i4%* :«■«•?. ttvii i.- ,- i-cc^i.' oj^W < Q f • . ' . '' tj ■ •■' • ' "“ £, ' " u o^r.-arSf' r-i^' -to [ ■.-' ^'' • *' ' ' i'‘ 7 l ’ ' • , . ' . iT , , _ . ■'-'i-i *'■- i' '<4 ■ fiC ja-ij ;. ' 5 \>i.', ^'tbgt >4JL/u:, r«'f*r ed !Am,f S i:'»iii>i'Sf .• 6 ■ftf^.:iffi‘:'4!^0'^^^^isi t>\ -tbiy;!'* ,^s^' a , . ','4Juf^; , p'^C' A, i “Jf ; & ' f A . .^ r,> T; '8 ^ .<1 *-i r /Ortki t P' '^s ' V ? ' 1 i''y'^^^'j^'k''‘ '^ 1 ' * 4 “’ ' ^ ■ ^ ■: , ■' ■" t:'' r ' ■' TM'^ -5- crease in relative humidity, as he maintains; but since the en- vironmental factors were not under control, temperature may have played a part in bringing about this change in the growth rate. The agreement of the growth curve in Cucurbitaceous fruits with the changes in relative humidity, observed by Clark ('78), Darwin ('93) and Anderson ('94)jmay have been due to conditions of re- lative humidity alone. Since, however, the periods of high re- lative humidity, recorded by them, occurred when the sun was ob- scured and the periods of low relative hiimidity when the sun was shining, temperature may have been a very important factor in- fluencing the rate of enlargement. The increase in the growth rate in Dendrocalamus during the night over that during the day at Perad.eniya and Anuradhapura^ recorded by Smith ('06), suggests that the lower temperatures, obtaining during the hours of dark- ness, were more favorable to growth than were the higher ones characterizing the day, and that this increase was not the effect exclusively of an increase in the relative humidity. The in- creases in the growth rate in plants during darkness, observed by Sachs ('74), indicate that factors other than light may have been responsible, in part, for this phenomenon. Owing to the absence of proper means of controlling the environmental factors in previous investigations, little is known absolutely concerning the effect of relative humidity on growth in plant shoots. The problems in growth cannot be solved from observations on plants growing under fluctuating conditions of environment. In order to be able to draw correct 71*, ■• ,-_^J f>MW/Ww • *'i' 1 - M i i‘ I’v.'lfoi^ rt' ?» i *■ ' } ' * .' '** '-'t-’''''*- ' •-. 1 l.'n ’'.'■'Blr-' M .'.Na' . -V t '' I V. @ ' ■■ ^ u' •I'l ' i'^''-'*tJilj||W .■'' 'v.^' . ' " ' ' 1 '’‘kJH ' ' ' i'f'") ■■‘‘^i- ' ^ ’ ' *!>»- ^ ^ . '■ f / v’.V -,' > ■ ' • ,• ■ u' r. ^ »V -^1 I . ^ ■ ■“.’ * ;-f r ■ -■’ ■ '^' ^■'•’’ - ’.'J . -, t'** 'i.‘- V .L#< K'v'i, :\ ,n ^4.' ;■.« .ibi ■; '- ' ■’■ -•. i'V'. ■' \^- ’■■' , ii * ' ' ■ |i ” *•■ jv^ _ ^ ••) 4 i!;s ', - . _•? S^'.'' ' ' ^ ; '* ,j5i^ • .j-'u: . ^''0^\A !?*”•; ^ »i' . t i 4xtSiXA r:*iW-r» ' '"t"' «•• '*^ 'A VJfU A. 4 . Ml • /. Vi-'' 1 , .irw'x ■'. •; /• i it ' r* ( i’ * -;l f 1 ». \ ■ ' . e rt '•-t ■ , ; ^ / *>.rl1 :!•?" ^V^.i'v v t5i /rr.; -. *i •/r.'A.A •‘ *,>i‘ ■ J Ir r. ■■ ••■ : .^' 4 . 'Tv;^S't / ' . ' I ' •A.' .. -v.U' 'V^-fi . I;-. '■ '. "■ ■''••'"' ' fii S' rirMiiC' . Y j if, i (vC i ■ ^ f / ;♦ rlli fii ^ ^ ^ w ’r ^ ' .j ^ ■.*•’..• .V to''':'- ' - 8 - one under a bell jar and one in the free circulating atmosphere of the laboratory. He observed that the growth rate in the plant under the bell jar was much greater than that of the plant in the free air. This increase in the growth rate exhibited by the plant under the bell jar was due, he believed, to the higher relative humidity obtaining in the atmosphere surround- ing the plant. Where the humidity was not controlled, growth during darkness exceeded that during light. Later, he was able to show that under conditions of constant relative humidity growth in plants exposed to light was more rapid than that in the same plants maintained in darkness. He explains this dis- crepancy on a basis of h higher relative humidity obtaining in the absence of light. In further investigations, he found that growth in thickness in stems of Datura was proportional to the relative humidity and that Datura leaves exhibit a more gapid growth by night than by day. This latter observation can be accounted for, he maintains, by the existence of a higher relative humidity during the hours of darkness than during the hours of light. The researches of Sorauer ('80) on summer barley show that with an increase in the relative humidity an increase in the rate of elongation results. The plants grown in a dry atmosphere, however, were stockier and possessed greater fresh and dry weights than did those grown in a humid atmosphere. Later, the same author reports results obtained from subjecting ^EfcW r>/ >»-•• -■ ■ M~. :tW '•«C VffZ , ‘ ita »■ ? ; > 1 ^ 1 ’. '■■'f‘<‘ • fVi . -■ J". tv -in-i - ’i- . , ■ r *T'ni few ^ ^ vT- .fS • . '' r, ■■, .■ ' . ... A.i>-*-'i:, ■■“ - ;.; ,i».^ 2»', I.. ' .xmxihJ 1 ■ ■’• '■’■ . ;■ r".'/^ • ^-'“' . ,'i "■' ' ;'f4>'^! ' ^ ., .. .^. ■ X'4-x . ' fc'. 5 Xj' ^ 9 - plants of Pyrus communis, Vitis vinifera, Ailanthus glandulosus and Lupinus luteus to dry and to humid atmospheres. His observa- tions show that in plants of some species a humid atmosphere accelerates growth, while in plants of other species growth takes place more rapidly in the presence of a dry atmosphere. In Lupinusjthe plants grown in a. humid atmosphere possessed longer stems and greater fresh weights than did the plants grown in a dry atmosphere. The plants grown in a dry atmosphere, how- ever, possessed the greater dry weight. Reinitzer (*81) demonstrated that atmospheric humidity plays 3 significant role in determining the rate of elongation in plant shoots. By subjecting shoots of Evonymus japonicus, Tradescantia viridis and Nerium oleander to dry and to humid atmospheres, he observed that the rate of elongation in the humid atmosphere was from two to four times as rapid as that in the dry atmosphere. In pea seedlings Vesque and Viet (*61) observed a great difference between the growth rates in dry and moist atmospheres, respectively. Without exception, elongation in roots took place more rapidly in a humid atmosphere than in a dry atmosphere. In shootsjthis was true in the case of one plant only. Taking the average values, elongation in shoots . proceeded more rapidly in a dry atmosphere than in a humid atmosphere, while in roots the converse was true. Hellriegel (*83) demonstrated that under favorable conditions of soil moisture a low relative humidity may be not » 4 4 r: ;i^ '.u.a:.: ;T;.C-y.&_^i;:'i:7 1 '^ •*'•*. vXt«yx /.••:■<■ ■ ■ N iii.%\' n :• [..':■ j sTj-rn^j - 10 - less favorable to growth than a high relative humidity. Plants of barley, grown in a soil whose moisture content varied from 30 to 60 per cent saturation, made as rapid growth in the pres- ence of a dry as in the presence of a moist atmosphere. He ft * states "Diese Anderung der Verdunstungsgr6sse tLbt aber keinen Einfluss auf die physiologischen Funktionen der Pflanzen, auf ihre Produktion und Gesamtentwickelung aus, so lange die Boden- feuchtigkeit innerhalb normaler und gflnstiger Grenzen erhalten wird". The researches of Brenner (’00) on Snmpervivum assimile and on Sedum dasyphyllum, indicate that a high relative humidity brings about an excessive elongation in plant shoots. According to this author, plants grown under very humid condi- tions resemble, in respect to height, those grown in the absence of light. In Sedum, he observed that at distances of 1.5 meters and 5.0 meters from a window and in the free air seedlings made, in a period of 14 days, a growth of from 3 to 6 millimeters and from 6 to 14^ millimeters, respectively. At the same distances and during a period of similar length, but under a bell- jar, they made a growth of from 5 to 8 millimeters and of from 10 to 20 millimeters, respectively. Unlike the results of Brenner are those obtained by Schaible (*01). This investigator exposed potted plants of the bean (Phaseolus vulgaris) and plants of the same species, grow- ing in nutrient solutions, to a dry atmosphere and compared the growth rate in these plants with the growth rate of similar J T j. rr : ,'' 4 . '.'i( ■ r ' . ' _■'>.. . i, ‘ J*r ;,Y>; .. ™ r.' ' . :ln ■'i'A? , ■i ' 'V‘' W ->> 1 - '*^io')iS"'ij'*isX" ▼«ffi£d , 16 ^- ;. - 0 s^ 4^^}^ M :|.i ,Wh 4 bw?ki£ oi.'^ ^ W- : ’V -V* ,»e S '! • *^ ■ X. 6 W fU: *;xV 6 .i^' lo ’ '• . f* .-•••, _>J.' ' i » ’ • /• ;*Jt f^-u{l OS ttldXr: . '; iv ■%;., s •*. ' ‘ ’ . ’• ■ ' ' ;.•*• ■'• ■■■ :\.W:A.'?k-.' ■ -V j ■ je ,♦ 4 ^'f(tE 9 iWk^\o ^^i . 'IR 4 ^ar*. ,Ti /V > . ,, . . , _ ■•<■ '“.i ■ ^ «fjylT^.^q[iiti3 vro (Ou'; 're/!!Tflt:5 a if '•,'*' I ^ . h ' h-i T '*’’* I ■ ^aEai 'n ^ . f Cl . I' ■' iyi d^rXif. [ V^^zk y:. or ^ , -ctl' • ' /.’'J ''' -- /• ''o. ■ '■,.'• f ■■ '“■' .. 5 ...^’jwrfrf-.V^ • I'**; <, .*' * !■'-. '■> ., 1 * -1 ‘ f ' ;'*.'■ f V ‘ - •'■■m tilts >I oj ,> (•' ... 4 : «* r X- . : »■ ■’" .'Vi ./' ’■’ ’^'- ■ ' *^’-' V'iSfi ' lo ixi 4 B 5 B ‘’■|ftc-'? 1 r raidlt X9d.t^ "'I ■•'{ 1 iv »'.’ • ■'t" ^ . . «X%v .aV^-.SSriifiiE.O't; ••'' ... , . .1, ■ ,.tt... ; , , y. , .. .. I ' l^ ^ ii> Ti iy jo » >ij q>i » adrw^ - 11 - plants growing in an atmosphere charged with moisture. In one series the atmospheric pressure remained normal, while in another it was reduced to one-fourth normal. Under both conditions of atmospheric pressure^ the growth rate was more rapid (and the leaves larger) in the plants grown in the drier atmosphere. He states, "Nach diesen Resultaten hatte die Luftfeuchtigkeit kein- en Einfluss gehabt". On a basis of dry weighty Ts chap lowitz ('66) found that seedlings of Pisum sativum growing in a dry atmosphere exhibited a growth rate unlike that of seedlings of the same species growing in a humid atmosphere. He states, "Wie Zahlen ergeben betragt das Gewicht der absolut trocknen Pflanzen- X substanz der oberirdischen Organe der in den HSus^ mit der hOhern DunstsEttigung (63 und 47^ der relativen Feuchtigkeit) gewaohsenen Pfianzohen bedeutend, nahezu 14%, mehr, als das der betreffenden Organe der in den trockneren Vegetations- raumen (mit 46 und 39% der relativen Feuchtigkeit) erzogenen jungen Erbsenpflanzen" . In plants of Phaseolus multiflorus^Godlewski (’91) observed that an abrupt decrease in the growth rate resulted when the plants were changed suddenly from an atmosphere possessing a relative humidity of 64 per cent to one possessing a relative h\imidity of 38 per cent. This increase in the rate of elongation, however, persisted for a short time only, and the growth rate soon assumed its former value. On increasing the relative humidity from 38 per cent to 87 per centra sudden r ^ •(V' '*''' i '•’■■' 'S' ■'■' ■" ■‘"^^’■K.'-’lV^''' "*'''^ '''^’'' ■'•^'''1 •,*.'1'^^*' ' ?■ i '\x^v>^>P . . -i ''',■:: ^ i rt- «(XAaS e*?f’'Tfi"*cJ^S' fc.fi .-.i.'.(!*i*i!.4 I "■ ^ - 5fi^9 | ’< ■’ t'-*'’ M- ' •■’■r.r ‘^■ '1 : ' ^£<: Oij >,CtX ; ii' s,' / ' ' A' ' > ’ •’ ■■' '^' */■»-■ ' \’ i ?.:=^ J C •! ^ *^v;j v^'rA^-'^ V .* • • - '■• !,^i-r, 1 1 ' edt' •tr&fr -,»# .. i. ^* _!•. . VC* ••,*#•.. ... • Vj!>f 'irv ■- ■ '^ '. ^ ■ 1 ! ... ■"'■ ■■ I i I .; ‘ :. -u.il Xi^c. ‘jsfi.t-p.ua j;-- u.*'*'-'- ’'-■A. ... r ■- 'il’'.V'.^7 i,-':''M.;’ . k.'.:'l ^,Xii.- • ’5 1'Vs W V »•’. , I > ■ , -•'■..•/i ^ 'il;;-) Si'i, ;.i '.-.V.*-* .* ,; ..J ..MJtH' - ' ■:‘\u .' . ‘ \i C S.A'i f' ’ . : ■■-' i ! ‘ lii r^'. (r\ < " ■/ f' ) y V I ► rtX ■'■■■■ -I^' I , 4 :.. '.. i •■ - •. *• ■=, ; :-’^,..i'. i/» ' ' ' ’‘/’/■'-i j" V :> ’-■'■ ’X*' ■ir.- J * * *.,;•» >4^ ’ ov: < d ..iTi.oi, ... j' -,c-ii,:.::^ .. ,■ j u/ . ■• .. '■■ '■■ ' T;t 'i . .■■•;, 2 .,-o» j^JUL r •,: ,v . ^.vT ' ■■■'1 ' ■ . .'■ ■ ,.i - -.r ., I : t/i; r«x iTC^7U:'i/ .. . r:-^' V:*. v-” ; W«..,t. .*■’ 'i V.,4,;f ■ ' 1 ’ . [' , ... -*r J ttil.t •■ , r i iu"’ <: ’. ZiJ\r -C‘y “^-. - > ■■’■'V’?'"- -13- relative humidity. At times this correspondence was perfect. At other times, however, the data suggest that some factor or factors, other than relative humidity, were operating in limiting growth. An attempt to study growth in relation to atmospheric humidity, in a systematic way, was that of Wollny (*98). His reseaJTches in this connection were confined to plants of bar- ley, vetch, lucerne, flax and potato. In general, an increase in the relative humidity brought about an increase in the rate of stem elongation and an increase in the production of plant substance, both fresh and dry. One of the most extensive investigations on growth in plants, in relation to relative humidity, was carried out by Eberhardt ('03, '04), Plants of many species, including Lupinus albus. Mimosa pudica, Phaseolus vulgaris, Faba vulgaris. Coleus blumei, Ricinus communis and others, were subjected to three different conditions of relative humidity, namely, "Humid", "Normal", and "Dry".. The plants maintained in the "Humid" atmosphere consistently made greater growth increments than did those maintained in either a "Normal" or in a "Dry" atmosphere. Likewise^ with but one exception, did the plants maintained in a "Normal" atmosphere make greater elongation increments than those maintained in a "Dry" atmosphere. Similar to the observations of Clark ('78), Anderson ('94) and Darwin ('93) were those of Lock ('04) and Smith ('06), — ■ I '\ , , 'I ; V -•* . 1 * r . ^ ’ ■; ' '■ y' ■ '"'V !^ ■ i,^- r • • ^''»**•/^ •. ^ » • '•'► V w. IV f|' is ‘ *A#t- t'v: ,£*‘S~ 'fl.'iii: * . . • t.A-‘t | r‘!'.*f' r • - ■ ■"' ¥ J , 'C jtc^ :'• V ; fic^j r>. \c - bflA , ' TjL- jfivi ' k'l; L| - a*; i.^-fy ■ r ;■ t.* V '’-r;' '■ V'' '■ - ,;' ; •:^JW «AV . .. 4 »-’.;‘ -■•■■- •^ 2 '^ ' . ‘ ‘ ; . ,;'■ . '^ : ■' .^''■. •■ '■■•.? , ^ ,.' . . 4ij/n.ri>.vXvfii, Ay^ioa^^y. . • ’ ' •■ • •" / ^ ' ■ ^ ■■ •, . .iV’-ibiJ-; ■ u> .:JV ,'t^A ■ ». fi , ' , * ’'>1 ■ .' » r j ••' M\. V- . ; ... •■ r :i ■;:• IH : * "«'r,L- 1 c| '^ksktloX!, ' . " ' ' ' ■.' i .J • "•"** ,. ■.;,*■> 'V.‘-rT .■:ir, ». • .t'tv’X-- . . ‘i-c - ••: rit r/.':. ' ■’’tr'ii:* ,'’ ^ a,T i.^U io5P’ itfv .y.-” ■; V: '',:-i:,u*#'; . ..: ^ -' ’. ' • • • T'i f. ;- "s..- .T ) ....:. Ji'C”.' * ^ m;^w j .. *. o ,. .£..4. '5 if- ,v'£.i,1»9iU J irei'j- etfi^'r-.’f.'rCCi'X '',70 ■ :• 'Csi . ■•■-■-’ iv ■.•i • * ' ' ' ' ' , ■ • • **T* ^ ' ,. ' r^'/' iV •■ .- .. .p ■:%- '* ■ ' . -ic..' -\. '■’ ■jfr? ■'■ '■ o^u (■. . ')> ir ., ■' '■ ■£_« {■**»> ' )'■■ > #f ^ -• » -14- Smith observed that the growth curve in plants of Dendro- oalamus giganteus followed closely the curve for relative humidity during the day at Hakgala and during the day and part of the night at Peradeniya and Anuradhapura. In shoots of Capparis, Stifftia and Eranthemum oinnabarinum the growth rate during the day showed a close correspondence with the relative humidity. Measurements of fruits of Artocarpus integrifolia, taken twice daily, morning and evening, indicate a much higher rate of enlargement during the night than during the day. This^ he believed, was due to the presence of a higher relative humidity during the hours of darkness. Lock’s observations on Dendro- calamus giganteus, Gigantochloa aspera and Bambusa spinosa were similar to those of Smith. Rate of elongation in shoots of these O species, was found to follw closely the fluctuations in the A amount of moisture present in the atmosphere. IV. MATERIALS AND METHODS. The experimental work upon which this paper is based w^s carried out on seedlings of the common bean (Phaseolus vul- garis) during the winter months of the years 1930 - 1921. Two adjoining sections of a glass house, in which the heating was under thermostatic control, were appropriated for the purpose of carrying on the investigation. Through a system of ventila- tion in combination with steam heating, the room temperature was maintained easily within the desired range. The excess light. ' ^'rt;rV "'- 'b "^•j i ' '■ '^Hh . I?' .==■ :'.4r nS-.'. It-, /iff isi^xto 5iJif i[J8A? ^ ■if-'' Turtt'^ -A4:^X^*Q‘ip Jbrjs/ vxX KS 'i ' ' itl. '• 1 . -X'V'. ■ ' >’ ■; • • d3|hp;fi< t’iiv aiiirXiaasiXisXc*'' F '" ' ' . ' • ^ > ■ ‘ •. '*•, 1- ?■ •, _j*.‘^>j-_ '- " T' ' - ■ ,^- '<’^ ^ '’■•*' 'vT -; -X . ' % •-'■ ■'* ' . > V"'' • '■ ' V .’■ ■'-. ' . ^ ■- Jsn4^»X*TiO’i e^tyr,^ -,' ~»y .' ■ IQ . ■ hi \ i ^^z, 3b £UAi§ ‘'iSkr ^nixi'V ri'"'* i ♦■ • * \ ■ •-< • ^ • <• ' ' . ;. ';•* . . .. byiJ-i'Xs’j B ’iro i-if ’ '• ^ « ■ .'t T . , ■ * "V _ ,-j^ 55 /fv • 1 trUP^ v , ;i/ It ■ , , '' rg’; rJt- lifrrt r,|^xq aTpj|ie« *io ''•' - J ic < r^ ; : r? ■ ■> Ic # h, .y- i , y.i f': ; . i;.v ' ■■ '^v,,^ / • ' , '-- • , , • ^ J .Jjil:- ^ ( ,k y. '.H I I- . , - „ I V ' ■ -S^xh., ■, ^ fvcl', 6 f{ j id jil^r -■, 0^T£ 51'^ (n.i:;dS F\‘'- ' ’ ■* ' ' >> '■ ' ' ' ^ h' ' ' ' • ' ■V;'''. -'"^ ,• ^ ■ <'» , . JJ '■ ’" '■■ ■*' ' V ■ •'. V -. •_ -'■ ' ^ • '■ • ■,v,T,..':^ fl>, .1. ,_ 'J ' ,. . . ..,' • • ^ 't-< .... ■ • V. t, ^>» rtOcX ^4;^^ % flo3';?Aaid|jJpi?^ tr/ ^ [" • ■ ' • . .♦» - «< /*• •. >f V ' 1 . I ^ ;,T * ' ' . ^ ' ' * " ^ ^ ■ ' "’ij ■ rxiHt . \Hb 4^ j . '■ >/V‘‘._, < .. • •' , ,i /^.rrSii .'.^ j -15- on sunny days, was excluded by a coating of green paint applied to the inndr surface of the roof, and where necessary the plant chambers were protected by light shades. 1. Apparatus. The various forms of apparatus used by previous in- vestigators in attacking this problem have been of a very im- perfect type, and the conditions as stated in their reports are, at the best, only approximately correct. Brenner (*00), Eber- hardt (‘03, '04), Hellriegel ('83), Reinitzer ('81), Reinke ('76), Schaible ('01), Sorauer ('80) and Vesque and Viet ('81) employed bell- jars, while Godlewski ('91), Wollny (*98)and Bovie ('10) employed chambers in which to grow the plants during the period of observation. The atmosphere, in the bell- jars or in the chambers, was maintained either dry or wet by passing the air, as it entered the enclosed areas, over sulphuric acid or calcium chloride, or through water. To further assist in re- moving the moisture, Sorauer placed open dishes containing sulphuric acid under the bell- jars, and Schaible relied on this method entirely. A few workers have given the actual values expressing the relative humidity obtaining at the time; while others have merely stated that the atmosphere, in which the plants were growing, was dry or moist. In no case, among the investigations cited, was the relative humidity under auto- matic control. Since it was desired, during some of the present A t ’ '"I /■•SI f \ •* *>«■ $ f.'ik I ■■.' \ .. "-/• ■ ■■/■•;» rr ..' .. f » ,cw‘ ; r':^^ ; i • i t CCg' / ■ d ( . , .pff Ic^ti 'J. famni -16- experiments, to maintain the temperature of the root at one point and that of the shoot at another, it was necessary to em- ploy an apparatus by which the temperature of the root could be controlled independently of that of the shoot. Preliminary ex- periments showed that this could well be done by utilizing a con- stant temperature water-bath, in maintaining the temperature of the root, and a combined temperature and hxamidity chamber in the control of the environmental factors of the shoot. Water-baths . The water-baths used in maintaining the # root temperatures consisted of galvanized iron tanks, 20 inches in width, 7 inches in depth and from 3 to 7 feet in length, filled with water to the desired level. Heating of the water was effected by electric heaters, two in each tank, under the control of a thermo- regulator. The temperature of the water was maintain- ed uniform throughout by a system of aeration. Covering each bath was a sheet of an asbestos compound, known commercially as "Transits”. In each sheet, openings were made for the accomodation of the plant shoots and for the lead tubing which conducted the air to the baths for purposes of agitation. In one of the sheets covering each tank, two additional openings were drilled, one for the thermo-regulator, and the other for a cork supporting a thermometer. The openings for the plant shoots were nine in number and measured one and one-fourth inches in diameter. These openings were arranged in the form of a square, with a distance cf four and one-half inches from centre to centre. -17- Plant chambers and air-conditioning apparatus . The plant chambers and the air-conditioning apparatus, employed for controlling the environment of the plant shoots, were essentially the same as those described in detail by Hottes (’21). During these experiments, however, the walls and the door of the chambers were rendered opaque by a covering of heavy paper boards. Since a means for cooling the atmosphere in the plant chambers was not provided, it was necessary to take special precautions that the temperature of the air in the room did not exceed the temperature of the air in the plant chambers. The temperature of the rooms was kept down by adjusting the thermo-regulator to give low heat and by ventilation on sunny days, when the air temperature in the house was likely to exceed the maximum desired in the plant chambers. The apparatus, arranged as indicated, worked admirably well and gave highly satisfactory results. The thermo-regula- tors and hum i do- regulators proved very sensitive to heat and moisture, respectively. With these instruments properly adjusted, the atmospheric conditions in the plant chambers were main- tained constant to a marked degree. In respect to temperature, the variation from the mean was kept at a value less than .5*0. Records, given by a humidograph, show that the hum i do- regulator is capable of maintaining a relative humidity with a fluctuation of less than 2 per cent. To avoid making unnecessary claims. w I fL< . : li v,l'. ' , -l’ .V'tN ' /' 4 at’ i' '^ ^^ ■ '- V* ' fyS i' '>)> : . t -vJ,J ;t*iT*.u\: ; -:.i- . ■■ ) ;"r ^,ini4 : r ‘. .■ ' A ■'. ti '■4 ^ j. v; iu; ■ ■' - • «i . , ' ' A •' ; 1 ■ ■ . ,:. ;.Vt^I,;,o / ’ (1 ^ <»< ■* ‘‘V .* . VM-' r 0'' ■ c : ,' il-Vw'?' . ‘if ' t 1 J ■ 1 . • wi ■ 1 j ' ' m ^ 4 / ' ^ 1 , V , I -■ , *, . '■ . 1 » \ 1 1 (/’;!'■ 'C i >. i !>■ 4t ay. <•* - J.. , j ; cr .Jn- . ■ \ ♦ L. L V '^'.r *hJ/, t-l' * ‘■'■ ^V'*’ **v ’ '■ ■ ' ■ ;., ’t'V)*-' V ■' ir w 'I *• ^ ‘T i'*vT M . ,1.'. j.:ti . , ,■ * ■; ' r ,v ■ ' ’■ ■hr, ', . ‘ 'V «t. ' '1 ' . ^ ^.' >■([■* -.' /V '■• si •, ( ■' ''/»■&'■’- ,4 ...S' • V- > * ,' 4 ,' ^ r ♦, . ' ,* ■ j li: V .f. r >■'.'■ ,'■* if -I’.'V , • *»i 0,! ■ !• *>, M', .. .. ^ M , ,k' J J. ^ -•’i i' i.! •iVJ *J .■ ; . ;''V»i ■•; r - 1 ■ *, A * . < V i ' ■ / '-Vi:, ■ V' ' . t- .'^ r''^' , j->i' ■'■ , . ... Uio',' ‘.w *..,'r.'.. IJ ri-'V, ' . ,'S tA , I. ' -la- the variation, during this investigation, may be put at a value not to exceed 5 per cent - two and one-lfialf per cent in either direction from the mean. A variation of 5 per cent in the relative humidity is not excessive and, within the limits of these experiments, is as little as could be desired. 3. Preparation of Seedlings. As previously stated, seedlings of the common bean served as plant materials for experimentation. Seedlings of this species were chosen, owing to the ease with which they can be grown and to their great adaptability to laboratory methods. The seeds were of the Red Valentine variety and were obtained from the Burpee Seed Company. To insure seedlings of uniform vigo:>the researches of Blanchard (*10), Bolley (’01), Clark (’04), Cobb (’03), Cum- \ mings (’14), Desprez (’95), Fruwith (’17), Grenfell •( ’01) , Haberlandt (’66), Hicks and Dabney (’96), Kiesselbach (’17), Love (’12), Lyon (’05), Miller and Pammel (’01), Montgomeiy( *08, *12), Sanborn (’92), Shamel (’05), Shaw (’06), Snyder (’05), Soul and Vanatter (’01, ’03), Walls (*05), Webber and Boykin (’07), Williams (’03, *05), Wollny (‘77, ’87) and others (Kidd ajid West, *18, *19) show the necessity for employing seeds of uniform size. Though the investigations of Middleton (’99) indicate that, in the bean, size of seed has little influence on the resulting plants, the evidence appears to be in favor of the conclusions reached by the former mentioned investigators. Accordingly, the sample of seed, taken at random from a large >£jgidk- .t ^ . V & i) / ■ ■ ;;• .' 0 A% ^ 1 ^r\ T ■ i t ,ju', I* •> I .. ' ■' 1 . r !^:-i.L;-X' tc' fc/j';);,' ■ ■ ■• •- j J: • . I • > . ' i:^( . .r>.' r.- -:i ,ii i A • . :X‘:r *il4- .^k^^Cij'ru C>. ■.■' ?/ &V *'.■.* \ • J ^ r .A c-'‘,v;ui ..i;-:'' .. . . ■' ^ V* ) \ :»w, * ■■■■ ,. •f- * 1 ■ ■* ’ - U‘1-^ 4 ' • ^ ■> * ...s V' ' Trl . ' ' ': , (< ’ , 5&0 ■•. ,c \Kr' ^ - C-" < / -'to^ «v.o. . t ,. < ’•’' i WTi^k ■/(.;••'). ' . I J ‘ * •■ ca>iuc j W . ' - ^ V •' • L* . ' fri< V yo4^|0^^ ■ s 'V 0 .in I :. ■- ^7 . . . -’ / -I ' T /• lit i ^ dfc' # ■ ’ *■ i ;■ : ' ■> : .r v .7 Ji ' y*d iR ■ ......w.iX .>x:.r t •»-.•; >:. C* 7 ,*e.,- --•^• 4 ®^'' t ■ i, *ADT‘i.. * J) I ixj ■ . ',' 'i I 1 -19- supply, was divided into three grades, on a hasis of length, by employing a measuring caliper. The first grade included seeds more than 17 millimeters in length; the second those between 13 and 17 millimeters in length; and the third, all those below 13 millimeters in length. For the present study^ seeds belonging to the second group were chosen. In order to determine the relation between reserve (food supply) and growth, under the various conditions of mois- ture and temperature employed, each bean was weighed individually and its weight recorded to the second decimal place in grams. The beans were germinated at room temperature, in moist sand, in a germinating pan. Upon the radicles reaching a length of from 2 to 3 centimeters, the seedlings possessing radicles showing a small departure from the mean, in respect to length, were transferred to one-quart Mason jars containing the desired culture medium. As a medium a white silica sand, brought to the de- sired moisture content by the addition of water from the Uni- versity wells, was employed. The sand is almost a pure silica, and the water is in itself a well balanced nutrient solution, as shown by the following analysis, furnished by the Illinois State Water Survey (’15): Mineral salts KNO^ KCl^ Parts per million 2.3 .8 2.0 6.4 81.7 7.5 Mineral salts MgCOa CaCO, FeCO^ Parts per million 105.3 144.8 Bases Total 375.0 4.4 . 6 15.8 3.4 '■■' ' 5nv -^4 - ' -Ww '«.^tt»^.iii^W,i{i»^ .mm, X . m> m- ■^::. •rf Tf ’ ;ig '“ ty;j •■' ■ ' ’ ir'^^ir,-: .' ' ' -.. - ’ * • ' t. . .•v..';.- , ■IH^V.'l" ii&t ifX^'i i Aii^XS^ t ;!t ,JKirr a. r« j j|i)- •«’ •• • • . .',■.-,■ ■■••Mt ;•.: . f. .. ', • ■ >•'''>■ ; . f ' ■ .' ' ■ '' / A ' . ^' ' ' ■'■ ’ 'ft ' . f =.*Aff ,r' .J ua«il()a)ccto't .5*i%.t3f. ji, , y ,a.«i <;fcODCj^ <'' iiitl ' ■ ty ‘t I \v4t4fc ¥.i^X051 A'l:,;..,.*^!:.' ’ ■’. '<’ ii. , : •' ■ V M :.I ‘ ■ ’sV . '■', ■ *'r *-‘ ^ , .T ..■ ki*/ ) ^r't ’■ ia A j-*- -4 ■ ./ ;y * , .» ■ ^D'. 5f,;'*:.,}i^'vvi.XlI .fexf, 4 ■*•.%=•. 'tn^P'iKfQ . • J ’•’ . ;Xj . ; ^ ... '■ . :-:V?Sfc-rf‘-, -% i'. pry ■•.,«> if r : ;.. : .’ . .'■ '..' ■ . •' ' v ' ‘ vkv ; - iivV;/r ‘iteli ■ V ^t^p aX ,Sxjy.*^iifffc ’ ’Vr'l' ''' ■■'’'• \ " ‘ -• ' * ' "l 7 ‘ i" •■ ■' ■•.t» '-Ai ‘‘”.<* . ■■' '■ ’ ■' ’. " . /■'■. ■*• " ■** . - P--X^ i> '' ' * » ; (^’ )^ •’•{ibr.ai/a \it4iW' ™ kk- ..•■ .■'' •■m •”■;*" ^ >1 .*■'» » O ♦ ‘.. .% w. i'yi z' . f./ ."i;.>;v -ie;.:'^:- ’xBOsg*'!' :^r- J x*3ot ■'■■.7'ifv. ■*/-„•■ .-,> ■'.rrsEj^ , ' ,ri x *y rvx< >rri -30- To overcome the difficulty experienced by Briggs and Shantz ('13), Kiesselbach (*15), Montgomery ('13), Living- ston ('18), Brenchley ('30) and others in maintaining a medium uniform throughout, in respect to moisture, the sand was brought up to the desired moisture content before putting it in the jars and undue evaporation prevented during the development of the seedlings. The respective moisture contents were obtained by mixing together, in a large bowl, a known weight of dry sand and the correct amount of water. The weight of water required in a given case was determined from the value representing the water holding capacity of the sand, as ascertained by a modifi- cation of the Hilgard method (Hilgard, 'l9)» Preliminary ex- periments showed that, with ample precautions, the loss of water from the sand in the jars during the growing period of the seedlings did not exceed 4 per cent of the sand's total water holding capacity. To offset this loss^the moisture content of the sand, at the time of mixing, was made to exceed the stated value for each series of experiments by from 1 to 3 per cent. This treatment provided a sand with an average moisture content, throughout the period of experimentation, equal to, approximately, the values given in the tables. For instance, in the series run in a soil moisture of 30 per cent saturation and in an atmospheric relative humidity of 30 per cent, the moisture con- tent of the sand, at the time of mixing, was made up to 33 per cent. At the close of the experiment this value was found to be approximately 18 per cent. The average for the period, therefore, was 30 per cent. .■Tr ^ . :* ; J U ‘ • ■ ' • t j.'-'-^ * . >.w, ,..i sl.Utl>C - I \ N ^)r, ,JSj.iutj> t I.. ' . . . : - L. V t ^ - ■ Si . JL ■'>': 71 •/.-'' <> 3 i. • 7 »i';i ■•-=♦' ■ ' ■ \iif . : (jfc/'jV'Jf- '. tr%i. ■•YA’- • .' ' t/lU I •w«' s Jt;j ,J, . Ito t .J .1 ‘p>. , ■ ^ ' ■yrt -:.i'V ;4 '^- H' , 5 j : dv:iv .y '’.fi ,' - rJI ic jvol .1i - . 7*^-.? li ■ :-.a ••■'w^e.tl'tP’--, -,j i-j-.:. C • ::-;■ , t i :■.-. ;■ R> ’■ I ' ' . ^ / fisT’o. mit t '-. '■ irf- S- O'." . ‘ : 5 r: ' 6 ^j.. ,i • • ■: .■’ xno;i* , • fli j ^ 03 . ( :. ^ , o:i |'~ u f. fl^S ^ ■- ' / ■-•:• i 0 \3 a . i VI n-' ^ ''-f '■; -Tf:^ vv-'^WC•il§ll3i^: Iw iic If-.. . uii'tj a-iirxb '^^K7 y ■ i •( - -; . . Ivv ' fv' Kii orfir Vtt: r' Lr.'i- Vi:,! .Tri';; V.' V;: :•: C './ v-ii' »». ►fi Vo 'i‘«u •■ V . .-. , b,i: {.' : ■ ' ■ ; ?< :%V 1 *«■'•’. /'■:.« t^;.' '•-r *•->!%’ J • ^ ' ' ' ^ Oii.- ‘•C't' ^ -f •^-... . 53 Ju ;• ' ■q ;. 7 . » *r • A-» ■.S t( I - 1 - O' 'li^^ararr^ .- WjAVi'vrtt - 21 - To secure uniform compactness in the aand, the jars were filled loosely with the moistened sand and were allowed to drop a set distance on a padded board a definite number of times. After this operation the jars were refilled and, with a slight pressure of the hand, the level of the sand brought to the desired distance below the top. The germinated seeds were set one in each jar, at uniform depths below the surface of the medium. A metal cover, with a small perforation to peimiit exchange of gases, was placed over each jar. The cultures, thus prepared, were enclosed between two circular pans. The cultures were set in one pan, which contained a small amount of water, and the other pan was inverted to form an enclosure. The water in the lower pan was provided to in- crease the atmospheric humidity surrounding the cultures, in order to prevent excessive evaporation from the sand in the jars. When the cotyledons appeared above the surface of the sand^the small metal covers were removed from the jars, but the cultures were retained within the pan enclosure until ready for trans- ference to the water-bath. In all oases, twice the required \ number of seedlings were prepared, in order that those exhibi- ting malformations and that those showing marked departures from the average, in respect to growth rate, might be eliminated. Upon the seedlings reaching a height of about 4 centimeters, the required number for experimentation was select- ed, taking those that showed uniformity in height, and prepared for the baths. To the top of each jar was secured a metal ‘,'v ., ■a"':’''’., . '■' ' ''' ' \,s*' a: ;-''v t- ^ t’Sii ' ' .'''7i 3 • . “^ ■•>• ''4 try’i'y ' if*, , 't ’4 - ' '5_ . ytv^*^^yVB.,43<5 0r.'.6«wgrj£n ■ -■■ ■ - • . ■■ %-•- - '-v *^;' ■ ,;• ir*-. • ■•' ^I:«-ivf^■.•^lp ^-/eoiaui^ .f'l'^Wr »BlBc I ^/, /. fS-ff V * ‘-^ ■ ■ • -‘y''’ « ■'. t*-fr ■ 7^3 »;•:*• '‘'^^r*’. ■ 9-V' !> • '■( ■ "' ’ ^ * Jt'* i A'-, v4 fce-T-L^vW^s^if cfL li(^ id\sditoxii^l^ ' r ^R C QiS i 4 Q’i Xt' tt,SK 5-r; . sidSf^jC Cfd T ■' OuQ W^S tj , ' t''. ' '''‘j?'-.' ' ' ■ ' ■ .' '■ - “SVi il' /'■ * .■ ':'• ' ■.': ‘ ..y'''::' , '■ , / .' . -^'r ' ’ ... ■- ,yv r ' ^ .": ., p M 'm4% 'cti /i* ^■’ '‘ t ' .; ' M\i. ' .i'j; V -’.. r ^ •' ' ' • * m- *♦ t - Ji r^w ;X':^ ; 91111 \issf'^^lt:r»p:^y.‘ If fvj ' , • “/ ," ■ ■’. ■'! •• . ' .'>1. '. .'. *. ■ _ . »TjiEi.» /' •- •W A Skj'A . -1 *■ 1 ^ --4^ %7 ^ • -t" ^ ■«*<» > »» . 1 ^**1 -23- secured by paper clips to a metal strip supported by the wire upright. The seedling was held in contact with the combined scale and support by a small rubber band, sufficiently large to bring only very slight pressure to bear on the shoot. As a precautionary measure against the stimulation of growth, through the agency of contact, the rubber band was placed well below the growing zone. With this arrangement the heights of the seedlings were read with ease. During the early stages of growth^ the readings were obtained through the small openings in the base of the chamber, provided by the doors in the condulet covers. In the later stages of elongation, the readings were obtained through a large glass door, with which each chamber was pro- vided. After the transference of the cultures to the baths_^ a period of from 2 to 6 hours elapsed before the first readings were obtained. This was permitted^in order that the seedlings might become accomodated to their new environment. Readings on shoot elongation were obtained twice daily, with a period of 12 hours between readings, and the increments in the hypocotyls and in each internode were recorded separately. At about three- hour intervals, from 7 A.M. to 10 P.M. readings on temperature and on relative humidity were obtained. In this way a close check was kept on the behavior of the thermo-regulator and the humido-regulator. Occasionally an instrument failed to respond. t iw fc e Wt ■‘ 'i y A Vfcj" I ■ -^' 1-^ ■ivy: l: ..;•> f.i’o- ifXii tr Cii^ ■ \ ,*t* f - iWfv '- '6 '' 'J i’ , ' 4 ' ’ ... . (ft.-'. V .(? /• 1 1 ’ '•« / ' ' - . % >*- 1 --vv.V -V. r- ... ;eb*rc:<'iS'4;^ • • . • ^ e*. : '•• t - ..If. uT , ^iA V ' - ffcJC '•■\V 4.iXjft,jir ■ . ■ , MCi-ti',; /> y,C. * 7t, ;.. :./ £ . '.«■. ■ ' '.v'Vt ;'45^ '’"B ' ' « t ' A 4 *1 >'* . f ^ ^ ^ ' j6 *i'crv;.*ifr‘0 >>4y i' 'i . ‘ . - “ -■- ■• M'l ' 1 .' ' ‘ 1 I •■" ■■ 1 ^ . -V ' , j® - 22 - coger provided with a short bEass tube, centrally located and of sufficient size to permit the passage of the cotyledons and bent hypocotyls. After putting the cover in placej-the opening in the tube surrounding the shoot was sealed with plastic clay, The cultures were then labelled and the weight of each ;jar and its content^^S’ecorded. At this stage the cultures were in readiness for transference to the water-baths. These baths were situated, as already indicated, below the plant chambers. To permit this transfer^ the plant chamber, with its base, was elevated by rope and pulleys, and the sheet of "Transits”, which served as a cover for the tank and as floor for the chamber, was removed. The cultures were then put in position, nine below each chamber. The water of the bath was brought to a level of about one inch below the top of the jars, and the sheet of "Transits" replaced. To prevent the entrance of moisture to the plant chamber from the bath below, the joints were sealed with plastic clay. After replacing the chamber and its base^the growth measuring scale and the supports for the seedlings were put in place. The support for each seedling consisted of a heavy- iron washer, to which was riveted an upright of No. 9 galvanized wire. In addition to offering support for the seedlings, these uprights served to support a millimeter scale, from which the height of the seedlings was read directly. The scale consisted of a narrow section of millimeter cross-section paper, which was • -jr Ilf* KOY''-*^'-; * *•'* ‘ ■- ' >r‘i'-^ i’ ' ft''. , *> ■ t:- 1^ ^ Bn * * ■' ^■■' * ' ri? ' ' ' ^J®8p '*' *^^5^ ^ t^d;$-^^o^l-i-ai "iurSo.^ ^janiv^. iiil'' ‘ .»?4\ •’ /’ ■' . 'V-fti' .' ''■', '" ■•.^' 1 ’jfe Ic ci/'-.*«>ii I or'-^tlv ’ ii^AsSfwB '•!t^.a‘;-i >a.: ; ciwi[' • ,v^ ■ ^ '^•5‘^^o’^^i^ '%H' ''T.s - ■■* ' ■ '•-' •'■ W' f eWii%y?,WA l»Jf’‘jS^- ,.>tj ^a . s?Vi ' '" ■*.' , *V; f •/*'."» 1' ' ' ' I I ** • ' ^ o.il^J ‘ ^::^$’l:a- y-zyt* * !k .' 1 '^ W' '- . '■ ■*"* . ' ■'■■ . A '■ '■•.*/ii ' ‘.'f ?^>'-'r ’'*'•' ' ' -i ' ,. ' ^ '** *' ' ** w' ' ’*- ** \ ^ ^ ' '' ‘ "q K* i ,ivd^ ' • /•'>■ ■,, 't ■. • - V^. ,‘_r.v i 'J- ti ft4ie iLCfi. \.'> f p;^ rA&4' lo» <}J^- i '. ■ '« -V.-. "’s F .', ,'■ .' ', , *.-'*v .'i K5^;,V-'''' -fj « i:J}’^' ■ p '*■' . «>^.a ‘ ‘p J X. . adit to ' ' '' '^■•« " "T^- ; r ■'■' ^ '"■ -M'"'':.- :r\4 ' .,/ V ^ ~ ' ■ ; ■■ I' ' , . ■■■' A .’"y - b V’’ '■" ' ' ■ ■ ' ^ '4'f ^ ^ [. ■■••‘t,, - • i- '-m . ‘ . jTjf'' V' ■ ' ■ •' U* V'rft ■ ’: : ,>:yv':;”^. ^ '‘i* ‘ Ml . ■ ' W '• '’_‘^.;* “ *7 ■ ' \*- vi •<'«■.! ••-.,T' • »:• '■'. > ' { , ■• . . ,. .jS'^ ... * i r 4J6 x;1j» - i Xifif 'i,s di U '‘/tS ‘ 9 ;. Is'-'" .li| ■■fesfjM8X«u-^Xl n ^‘§Kt iO ' ' - ' '■'* ■' ■- .^■i'WiT >1 -.f. ,j/i • ■ ;.(,’■ _ ■ . t,.j,',^ !»nua .>jipvw a t8s>i w y ^4l l| ». ii rt « *^r -24- In such cases the data obtainedwere discarded and the ex- was periment repeated. Observations on each lot of seedlings were continued until the shoots ceased elongating. After elongation in the shoots came to an end^the cultures were removed from the baths and weighed. The seedlings were then removed from the jars, and care was talten to secure the entire root system of each plant. The particles of sand, clinging to the roots, were removed by washing in water. Be- fore weighing, the excess water adhering to the roots was removed by the aid of dry cloths. Immediately following this washing and drying, the fresh weight of each root and shoot was determined and recorded separately. After drying for 24 hours at a temperature of 30**C. , these products were trans- ferred to a high temperature oven (96*C.) and there dried to constant weight. With the dry weight determined^ the securing of data was completed. V. OUTLINE OF EXPERIMENTS. For convenience, the experiments are treated under two sections: 1# Growth of seedlings in continuous darkness. 2.. Growth of seedlings in darkness alternating with light. As already stated, the major part of the investigation was carried out on non- illuminated seedlings. These seedlings »■ f. ■' Ibijlfc '■•..I'” : i't;: '.> 'i^ A' ?i, ! '■( ^K-. «1 ' w. • r ^ -Ws’, ‘■■'■kp- ' i 1. ». ■•..: 5.-: : : , t' ■ i ' {V'‘ > ' 'Ilf iJ '-J \C 3 V*S^'-A •'• I'i^.k.,.? ;v- f; t ■ ::’t Wv . ^ -;: i 7 i'^t r*.;* if . .4' i * /u , ’C;?' 7'-’ ; ; i .V' 1 ' -. 1 ' ■ -tM . "■ ''^ihj' .i,^- "’^ '•■ ■■ , ■ ^ , . -1 ■ riC' bw, '• ■' '.V xi i c-^ 1' '\:V' • •• '..'•■a, Ir .•''' '1*45 f;:'' ■■;' ^ ‘4 X •'* ^■ • ' ■> ' 4-^^. 4 ••• •> Y.-1, ;T;':;;a;^‘V4:'^'> r . .- i . ■ ^ ■ ' ' ■ ' ' ‘ -'■'7 *5 ;JV^ ‘i *:•*' < it'? v'i.vf' " ,'. /t ' • if j i-'.f r ■ ■j .,.j (j.-o ^ ■ 'I ,*';'Vx',-v\ . .trtO i .T ;r;i j r IS V n j, v .iw , • 4 .ii-f M a I. « •".JVVi* - V « r- If lir^r ■" •,; ' '4. -25- were grovm under different conditions of temperature, relative humidity and soil moisture. The conditions obtaining at any one time, however, were maintained constant during the series. Lack of time prevented the using of more than one root temper- ature, but two shoot temperatures, three relative humidities and three soil moistures were employed. The root temperature, in all experiments, was maintained at 25 C. The other environ- mental conditions were changed, when desired, giving the follow- ing combinations: Shoot temperature Soil moisture Relative humidity ( C.) (per cent (per cent) saturation) 5 30 60 90 20 30 60 90 60 30 60 90 5 30 60 90 20 30 60 90 60 30 60 90 The seedlings, included in the experimental work of Part II, were illuminated from 7 A.M. to 7 P.M. Illumination was provided by light from the natural source, entering the plant chamber through a glass top. This was aided by the light from a Ray No. 90 Mogul Projector, furnished with a 125 Watt tungsten bulb. This projector was located 12 inches above the chamber. Under this condition of illumination^ a root temperature of 25 C. and a shoot temperature of 30 C. were employed. Pure silica sand, saturated to the extent of 20 per cent, served as a medium, and a relative humidity of 30 per cent was compared, in its effect upon growth, with a relative humidity of 90 per cent. '/'V , r':r " ; -L f;'*.-. L. , V, '.T «-'^T»5 ■'^■' -M: > '■.d’'-i..: -•.. i ■ * i6'Xi IZ'. 'L -• '■ i ‘' ■ .’. (c/ff&o ' 0.,' ;, • -.b s? ' :,'j ^?,’ ■'’ ' '■ •■ ■ ''^ ‘ ’■'■t-'"* V'J -' '' '':-A :ei^cX"v0tc««^ 3-rri 4 ':r'% ■ ' ' . s'i';cV V,:* i iV ■' I - I i )■ ( i ' ''.■OS' t: ► V t 4 “' '>!• Cf. ca ■ u Ml ■' -■■ ■'^‘ ' « '■“ .' 4 A ./•' »» .'/ .,-4Xr, ,Ti ’,: ■/ -f^ ' mj%. »"i /.ijitS , - -:-;r ’. '•'* '<. 1 ... ir ' '. 'k'- V ' f' is'i • X^'r ?.r. (fi .“ . 44-i 1 ; t ■ . ;■• 4 , ti ,& ' : If •. ., .j <, « ,. ... 4 ? iJtC' ■'■•.* '•a. , t Z 5iV.f y?3 .'■ ax e; viti -a •■:• k/ I ,, 1 v’^ .y'a. ft ^ ao ' . .03:': ,. ■.5 T.i.'v>*7i’';v; . ’rcn.'jr.^ri*. ■ jtu »> .; . . -.(Vl* ■v#<- -..1 Ho f k ■' . ‘. ■* 4 ->Oi.Xi>- I - ',. '#,•,' 'r' , - rj. w r* n-.r:- fHq.O&'h y ft - '7*5 '' , ,v i. . 4 ' f’f . ’ ' ■ A\ •■ . • I. wiiwiini,Mn|>4ijg i- '-.- ■■■■ ■'.'»•! -26- Seedlings growing in three chambers were simultaneous- ly subjected to a given set of the environmental conditions al- ready named. Since each chamber accomodated nine seedlings, A the data on growth, under a given set of conditions, were obtain- ed from 27 seedlings grown in separate jars. At times, however, some of the individuals exhibited growth rates that departed markedly from the normal. Askenasy ('90), True ('95), Lehen- bauer ('14) and others discarded such plants and based their conclusions on the data gathered from those individuals ex- hibiting a normal growth rate. This procedure appears legitimate and in the present work was adopted. In such cases^the number of individuals for a given experiment was reduced. In no case, however, was the number less than 23. VI. PRESENTATION OF DATA. Since upwards of 500 seedlings were studied individually, it is evident that the detailed data for each seedling cannot be given in a paper of this length. Even if it were possible to present all of the figures, it seems inadvisable to burden the reader with a mass of detail, especially when the data can be condensed and presented in a form that will show at a glance the relative values of different treatments. In the case at hand^the data has been much condensed, but the aim has been to present as much as is necessary for a clear and correct inter- pretation of the results. Bf;,’' "' r ' "T;V ■’* i- -M. iHiWWI \ , : .4c-ff( l;'ij v\:. „.y^- 'C^ £;.*».<■ ^ •• ' . ^ -"-c' ./ K...‘t? ’ ■X . ;•■...- '. . . .‘, V ■! ■ ^ ..-.^W ' ' ■ j.'-' i'i'i ?i f\A4 / /» («> . . X'*. ■ V- t ■: i .:. : kj^'V N; •>. . 0 )'. ^ .. . , Jl . n ^4 X ■*' fi U l/i .-X 'V !■!& 'V.c-.ir. •■ ,vua-, ( ■ • ,| ' ~J,‘ -■;.. .1. ::'!.* 1.5C i ^ t,. i. «!, L' ^ '■* f ^ *:c* U xc;i>$i‘^:>rpc- -J.’,;,| 'ff f 1 > •'■ 1 . 1 . ‘. .' ; •: ' -I :. »- ' Toli.! - ^ fi .;t ti:A 1^4 - v :', -jA -^i *i * . Aj :A‘ . .’V ■ 1 f.'.- Afv"'*‘%<4 :v‘fy .i-y- hr- "/: 'I I ilv..,,;..j-f;>v I -:,.a.A >i‘j : , :'c -• • ■';i.b >'0 V ' V "’ f -vlrfiTV ^ ^ V*-i • i? -t * ' './■ J i'}.-? - ■■lit .'fe i»! ■is j, •' ' i. ' ; .1 w rj , ■'.-' ■- .i :: ^C. "'“■ ,•.. :.'1V1 > ^[\ y i'> ■/ ’ L‘; i-fr X VC' r'tl' ■•«*> ‘V-’ • i > . ' ;T4 y:-^:r . -p --x* rf :. ^1 I. v.a4. ^!3^»i- ji< r, ’ •'" : , ‘ i : >=' >iri .:*■ ■; ;t< '- u. >• v,2‘-' t'c-i v* ^ ■ ■' , _' i 'r ; , ' -27- For each character studied,, the mean value and its probable error were determined. The mean weight of the seeds was determined from the values obtained before the seeds were placed in the germinating pan. The mean weights of the shoots, both fresh and dry, were obtained from the values secured at the close of each individual experiment. The average 12-hour increment of elongation for each individual was determined from the value representing the total increment made during the period of observation. From these 12-hour increments the means were determined. The standard deviations, the coefficients of variabil- ity and their probable errors were obtained in the usual manner (Davanport, *14). 1. Growth of Seedlings in Continuous Darkness. In Tables I and II are presented the data showing the rates of elongation in shoots maintained at temperatures of 20°C. and 30®C. , respectively. From inspection of the data in these tables^it may be observed that the differences in the increments of elongation between the seedlings grown under any two conditions of relative humidity indicated, in a soil either 20 per cent or 60 per cent saturated with water, are small. Comparing the seedlings grown in either soil moisture, the great- est difference in the rate of elongation, at a temperature of 20*0., occurred between those grown in a relative humidity of 60 per cent and those grown in a relative humidity of 90 per cent. With a soil 20 per cent saturated, the difference in the ',•.- . - If , V . V I' :, I ■ if ■ u t Jf >;..- vtMV * .-b 4 ’.: ' . % ' ' „♦ W •^.' ' !' . ' ■ ■ Sit. f fi tolled t^ii-.-’' V ■ ■*• k'^^:'J ‘: o : r I-'. /' . n 0 " V " :' ■ - ^ J - Kgi /-/I ‘ C \ , . 'iU<£),d ■'••« i ^ '',.r ". ''V ' (MI'v .' . ■ .■ - «f ■:-,i nrw" I ■p ^ " t'Ul LT .:/' .<* '■ '^j,. . .. lU : lirf "• ".'■ * ' f' c ; w' Aj \ { jrjl'cf - ■ f V * f '0 '! - : c ' 1 JCL ’ T 4 >/ u > :;> j « ■ i ,(:.l' <:? lOV 3 V.I)C-) \ ' a.v'i^.G ?o’> lU '^js w ^;X -, • '.• vV ' vvi'v ■1 ‘,‘'*1 acj . i ' » iU /).^ o : cii .; * ■• fe,r'J2^'jjEl3Ci^' ; J wT' lit)' ij' -*.'■ *•■■'■'> -•' J ;'■•■■ ;: I" i ' ; - . ^.4-^ ■ .',3-1. fjfii. lo ac.XiiO;5C ?tr;i ;i.’w:X'‘i ' , v f. piu- . ^ '^TC. ^.■■. :: ‘ ■ = - '■' •' . ■ , ■ - ' V , , 'i'- ■ ' L' ; : pri:^ -::i • i - -’-' , t ' i » it • - V* ^a^dP-V't >,n >. '■ r. '^' ■ 1 'i ~.: rii'T ' •} f%J ' ■ \ -^ ■ . y -- Ij O . r . J ^ S ' Spr :. ,1 ' jL": L ': r.: 'ep . ij;? C/i' ^ .• fc [iFf*'*' -O ' -': , r I * .■.,■/ . . ■ i ’■%» ti utiil '• V '.' •J C . '^y-. ... ' 'vj j V ■. ^. •■:;-^. C ^> *!;,i .' ;-J C ':. I • > .-1 t '.:;. 3 - /xC?- i f'-A' otJ' .!..’■,■•> 'if S ole V ;..■■-*£ *i >'.' I '-f f •-' ■ ■ '.. '.!' ' h .^ '> iJ ;.'■, .w .. t V ... 1 --..J ; yi‘ "t V : Atf 03 t»y ■ A '■' „ . , s V '} ' .’ . .’ '^/.asibC’T^A'V 5.* !j ■ ■ ' .'i! litr: > T:,- ■ ■ , ^ »., h'~. il i"< ''.r± .L^ . •::’1U r : crxit^r-^ ■;.■ Lt (■•. v' ..; , ao . J • . ** •> :"'C £>t-o: V-^ . i v?v •V\,-, ’ ) rtc;.' ■..• ir.: *j.r- ' v »viy<^.' :- ■ *•>'. ■tv , :' ■,. k> ■ ^1 ,i. i - • ■■•■Jj -Ci It. * i^n ■ *. w"^ Jb , < , ’ jb V rr-w"* f , ' ( ,.' ■ • - -‘ - (L 4. • '■ ■■ ■t \ . ^v . i , r’* ’ . t-y i''-[ ■■ .^m •' - L .L . , A V ‘ otfi* : ' i:-> i^} - ’ f"i‘ “ r eft ■1 J . , -29- of 30 per cent and the mean increments of the seedlings grown in a relative humidity of 60 per cent, at temperatures of 20® C. and 30°C., are 1.7± .32 and 3.3i .30, respectively. Between the means of the seedlings grown in a relative hmidity of 60 per cent and the means of the seedlings grown in a relative humidity of 90 per cent, the differences are .8- .29 and .7* .30. In the formerythe differences are significant, as the odds against the differences being due to pure chance are over 110 to 1 and several thousands to 1, respectively. In the latter j the differences are not significant, as the odds are less than 5 to 1. Table II. Mean 12-hour increments of elongation in shoots maintained at a temperature of 30®C. Soil R. humidity Mean Standard Coefficient of moisture (per cent) increment deviation variability (per cent (in mm. ) saturation) 5 30 13. 0± .19 1.44± .13 11. 1± 1.02 60 16. 3i .23 1.80± .16 11. oj 1.01 90 17. Oi .19 1.38± .13 8.li .77 20 30 19. 9± .20 1.54± .14 7.7± .71 60 20. 3i .28 2.14± .20 10. 5i .96 90 20. Oi .32 2.33± .23 11. 6i 1.14 60 30 21. 3^ .42 3.17i .30 14. 9± 1.58 60 21. 3i .23 1.78^ .16 8.4± .77 90 20. li .39 2.77i .28 13. 5± 1.37 A fact worthy of note in Tables I and II is that of the existence of a difference in the rate of growth between seedlings grown in soils of different water content. It may be observed that, at the three relative humidiljes employed and A ^ '■'I » j >f», .,<&ii- T At: (t : ' • ,1 { •: ■ ! Co . , •r;-' ■ ■- '; .' ■/ •/ X 'i o «’! .,- . i‘. ,-' ■ <"* %* 7 ... c of ' fr.' VMy A' •:•■>- i/- . I. ^ M' 7 jOJ: e.t ip;^f^r:.i, '"vs-fl J rir^ ■ :•' ' ■■'■ ' mr ' 7itV . a,6 1 C . ; . I ^ ■'» r. JT: ■ ft •* ii« h' 1 ; V, ■ ■ ■ t ( tK< I X«T'j wC4 •.;..'.'<-.u*:-v V • /•.~-ft'' '. ' • ■ '..X V "'.H' .';: :',] r O ,'' i -30- at both temperatures, the differences in the rate of growth between the seedlings grown in a sand 20 per cent saturated and the seedlings grown in a sand 60 per cent saturated are small and without significance. Between the seedlings grown in a sand 5 per cent saturated and the seedlings grown in a sand 20 per cent saturated, however, marked differences are observable. In a relative humidity of 30 per cent,, these differences are 4.3- .32 and 6.9i .28; in a relative humidity of 60 per cent, l.?i .30 and 4.0* .36; and in a relative humidity of 90 per cent, 2. 6* .39 and 3.0* .37. Referring to Wood’s table of odds it may be found that the odds against such differ- ences being due to chance, sure in every case, upwards of 125 to 1 and in some oases reach many thousands to 1. Since the odds are well above 30 to Ijit is evident that these differences are sufficiently great to insure that relative humidity does exert an influence upon the rate of shoot elongation in seed- lings growing in sand low in water content. In respect to rate of elongation, the standard deviar- tions, Sts given in Tables I and II, are only in certain cases good indices of variability. Since the value representing the coefficient of variability is dependent upon the relation be- tween the mean increment and its standard deviation, the coeffi- cient of variability expresses more accurately the range of variation. Table I brings out the fact that at a temperature of 20® C. the seedlings grown under the two extreme conditions. » > ■ - ^ ■■ 'V'lfi ; 7;r, 'K -.-. . - ^a, i'i: 'c^rs?*' -rvtib ^.;- ^ ■•.«•)■ . :•■ ?4xscf i-a ■ ' ^ V i ' ■■ ■' ■- ' ■ •■' Vptv’ ;t! ■ .. l> ' y- /, >.' V v". ■ V i ({. '.^ j. ^ V 1’ .• . .1 ■ '■ . '■ ■ ■ ' ' • ■'7 ^"-fr c-;.- • — r-'* - ■ . ' • ’ L '?,(!' ' "w '1-n . *f’rj.i\±rrl '-^'j ,.7Hi i'-'A ;lv/. . ■ i -yi: uO '.‘r \ t k r I ^ tk* ' -r::'" j 'iv- -sj ''■■ *< ^ 0*;^; [’Jcr-^ ,i.r„,;o us^v-A.‘*'h^j . - . •.' ' -■ : •,'*,? ^ 'x .lT :' . •• rny^.':.!!; sry* > w K/;r - . • " • 1 /' ^ . * • . t ^ tJ" • • ; ’■•■ . . ,' :j 1,?, ^ .t: b 1 fi'- 1 /»• r- V ' , • .V . '"j V ' . ^V. ■ -i *■*'■.-« bfi.r '2i^' 't ■ • 1 .:j ’::nifc’]c ,f’;< j. '. , - ■•.4a ^ l fellio io 0 ,X^'. .;‘:t.'‘ 4'u /l * 1 ‘,f /I ' iM ' .A • '.b'r 1 ' j • # ^ ft; ■i ”.c l: -■ /if <•'' V 'iy‘^ • • • :f-, ! , C'l'- ■.■.dtaV.Hf'.r - . ' •• to. .A.'- •:X X / L'.*r-_ *v ■nf:^:L.y -i 'v» 7 i.'. ' '• '; sSfOfi. j ■ ' ■' 7 .Vx - t I i tJV ■ Av Ifr, ^^C*i3S “'■ ‘Z^h'X t .'fXi/ .' - V; / ■ ct ■ ... -' . - V i " - ■ c - :iZt r i ■- , '• ■ ■ /( 'ij / 'Y7 <> ">i;506a“, _ •, i, :.; ■: -X '•'f .UJ* WtX*^ '• ■'» %■"(*. * O.i'jJlftPO J i'j t 1. ' 7. Hi? 151^ ¥,'3 -31- in respect to moisture, possessed the greatest degree of variability. At a temperature of 30® C.^ the greatest degree of variability was exhibited by seedlings grown in a sand 60 per cent saturated. Tables III and IV furnish the data supplying the mean fresh weights of the shoots of seedlings grown in tempera- tures of 20®C. and 30®C. , respectively. The values indicate that, at both temperatures, there existed a close relation be- tween the rates of elongation and the fresh weights of the shoots. The amount of water in the sand influenced, to a marked degree, the amount of material produced. These increases are the most striking in the rise from a soil moisture of 5 per cent saturation to one of 20 per cent saturation. Beginning with a relative humidity of 30 per cent and ending with a relative humidity of 90 per cent^the increases at a temperature of 20®C. are .50- .08, .36^ .07 and .81- .05, These differences are very significant, as in every case the odds sigainst such differences being due to pure chance are upwards of 100 to 1. At a temperature of 30®C., the increases, in the same order, are .64f .066, .28^ .067 and .27^ .066. In the first case^the chances that the seedlings in this group would occupy the same position, relatively, were the experiment repeated, are several thousands to 1; in the second case about 21 to 1; and in the third case about 20 to 1. Since the odds, in the last two, are below thosg^enerally accepted as the minimum for certainty, the significance of the differences are open to question. I ill »«» « -33- In the rise from a soil moisture of 20 per cent saturation to one of 60 per cent saturation, the differences at both ten 5 )era^ tures, are too small to be significant. Table III. Mean fresh weights of shoots grown in an atmospheric temperature of 20°C. Soil moisture (per cent saturation) 5 20 60 R. humiditv (per cent) Mean weight (in centi- grams) Standard Coefficient of deviation variability 30 1.90i .05 .41± .04 21. 3± 2.11 60 2.04± .03 .26i .02 12.6* 1.20 90 2.13i .05 .38± .03 17. 6i 1180 30 2.40± .06 .45i .04 18.5* 1.75 60 2.40t .06 .45i .04 18.6* 1.76 90 2.94± .07 .54* .05 18.7* 1.82 30 2.62± .05 .40^ .04 15.1* 1.41 60 2.67± .07 .54* .05 20.2* 1.92 90 3.16± .09 .67t .06 21.2* 2.02 Table IV. Mean fresh weights of shoots grown in an atmospheric temperature of 30® C. Soil R. humidity Mean weight Standard - Coefficient of moisture (per cent) (in centi- deviation variability (per cent grams) saturation) 5 30 1.84* .043 .33* .030 17. 9i 1.70 60 2.11* .045 .35* .032 16.6* 1.56 90 2.23* .043 .32* .031 14.3* 1.39 20 30 2.48* .05 .39* .036 15.7* 1.^47 60 2.39* .05 .39* .036 16.3* 1.54 90 2.50* .05 .37* .036 14.8* 1.47 60 30 2.47* .05 .36* .034 14.6* 1.40 60 2.57* .05 .37* .034 14.4* 1.35 90 2.70* .07 .48* .048 17.8* 1.82 In Tables V and VI are presented the mean values of the dry weights of the shoots grown under the various conditions employed. If the data in Table V are examined, it may be found -33- that the differences between the means for the shoots in any two groups, grown under the same conditions of soil moisture, are insignificant. With but two exceptions are the differences less than their probable errors. At a temperature of 30° C. and in a soil 5 per cent saturated, a relative humidity of 90 per cent has given a much greater dry weight than has a relative humidity of 30 per cent. In this case^ the difference is 3.4+ .54. This gives odds of upwards of 30 to 1. In the same soil water content, the seedlings grown in a relative humidity of 60 per cent exhibited a greater dry weight than did those grown in a relative humidity of 30 per cent, but the difference is not great enough to rely on it occupying the same position, relative- ly, were the experiments repeated. It may be observed that as the amount of soil water increases the dry weight of the shoot increases. The only marked differences, occurring at a temperature of 20° C. , are found in passing from the seedlings grown in a soil 5 per cent saturated to those grown in a soil 20 per cent saturated. Even there the differences are too small to be of much significance. A signifi- cant increase in dry weight, brought about by an increase in soil moisture, is perceptible in the seedlings grown in a relative humidity of 30 per cent. When such seedlings grown in a soil 5 per cent saturated, are compared with those grown in a soil 60 per cent saturated, a difference of 2.6i .54 may be observed. This value furnishes odds of about 50 to 1 that the difference is due to environment and not to pure chance. At a temperature -34- of 30®C.,the only significant difference (increase) in dry weight, brought about by an increase in the soil water, occurred also in seedlings grown in a relative humidity of 30 per cent. In this relative humidity, the means of the seedlings grown in a sand 20 per cent saturated exceeded the means of the seedlings grown in a sand 5 per cent saturated by 2.9- .55. This differ- Table V. Mean dry weights of shoots grown in an atmospheric temperature of 20 C. Soil R. humidity Mean wt. Standard Coefficient Per cent moisture (per cent saturation) (per cent) (in eg.) deviat ion of variabil- ity of green wt . 5 30 14. Oi .43 3.22± .31 23.0= 2.30 7.3 60 14. 9± .30 2.29± .21 15.41 1.47 7.3 90 15. 4i .46 3.3lt .32 21. 5i 2.22 7.2 20 30 16. Oi .56 4.21± .40 26.31 2.55 6.7 60 15. 7± .45 3.50± .32 22.3= 2.15 6.6 90 16. 4± .32 2.37± .23 14.61 1.42 5.6 60 30 16. 6± .32 2.43± .22 14. 6± 1.37 6.3 60 17, Ot .49 3.781 .35 22. 2± 2.27 6.3 90 16.61 .42 3.26i .30 19.61 1.87 5.3 ence, according to Wood, furnishes odds of about 100 to 1 that a similar difference would occur again under the same conditions of experimentation. On further examination of Tables V and VI, it may be observed that a constant relation between the mean fresh weights and the mean dry weights of the shoots of seedlings, subjected to different environmental conditions, does not exist. As the percentage of soil moisture was increased, the water content of the resulting shoots became higher. This appears to be constant under the prevailing experimental conditions. A fact worthy V V,- I. }■ V '. i'i ... Y J ' ^ ;Ct. ■. 1 ^ ' . •■ ^:|“ ' Jijj tt: ^f)o;' V -V \ ' V ■M\>. i, ^ •*■'. V ' • v'^ * f f. *'- ;■■ ^ • ft * ■ *?:■ : "., . ..r ct. Vr,;.i^- : tV.rrr. m. I. ■,^p. ■| ? /.*9 Oti .'\.. ,.4-' -V. ■ - V •+’ • :. ' '■, * *>--■ a \ ' '■ :. -' Xwr. :,' P<> ' ' ', J (V)f' ■'’„V I /-i ■ ^ , ' ' _. ' . l' • • '.V,. ■! ' ■ '^ “ ‘i'.L‘ {., ; ■ 5 ;-' 'tOti ' :, -, '“ ’* I . v^ l«4s’ £ 1: \-V w>h. *! j. ,lV i ,.4/)' ''to . ■■ .Ih ' , . . 'V ■ ■■....,' .i :v^' >M,C, • ’'/^ .: -T ^ • ./■ . f '* .. 4 * . . ii :)• x:l> >/tp ;.‘ ' \kj > « ' Asritsi * • - • t ® f.: y.Vt-. • I /: ✓ . .■* ' ' .'■■?>. "ji/’ . .0 bXo<''*.k ' ~ . .-!■ •i.’U xo. :!•■>-’: /A. .^tf’r-iTi^MCiy '• . ' ‘ 1 ,'> ^ j t. , ‘ 1 ' i V. A Ml d ijr,mii\''^‘'*^: ' -35- of note in this connection is the occurring of a difference in the part played by the soil water and atmospheric moisture at the two temperatures employed. At a temperature of 20°C., relative humidity exerted no influence on the per cent- of dry matter present in the shoots of seedlings growing in a sand 5 per cent saturated. At a temperature of 30® C., with the same per cent- of soil water, this did not hold. In seedlings grown at a temperature of 20® C. and in soil moistures of 20 per cent and 60 per cent saturation, relative humidity influenced, to a marked degree, the per cent of dry matter present; while in seedlings grown at a temperature of 30® C. and in the same soil moistures, differences in the relative humidity brought about only slight changes in the per cent of dry matter present. Table VI. Mean dry weights of shoots grown in an atmospheric temperature of 30®C. Soil R. humidity Mean wt . Standard Coefficient Per cent moisture (per cent saturation) (per cent) (in eg.) deviation of variabil- ity of green wt . 5 30 14.9* .41 3.2* .29 21.5- 2.07 8.1 60 16. .38 2.9± .27 17.6* 1.67 7.8 90 17. 3i .35 2.6± .25 15.0* 1.46 7.3 20 30 17.8* .37 2.9± .26 16. 3± 1.53 7.2 60 17. 4± .43 3.2i .29 18.4* 1.74 7.3 90 16. 7± .41 3.0* .39 18.0* 1.80 6.7 60 30 16. 9i .34 2.6* .34 15.4* 1.53 6.9 60 17.3* .32 2.5* .23 14.4* 1.35 6.7 90 18.0- .54 3.8* .37 21.1* 2.18 6.7 Tables VII and VIII bring out the relative values of different combinations of soil moistures and relative hiimidities in the production of dry weight in roots of seedlings. In the . • t. MW' ^'TWr^^ ' ■*: : m - ' • ■ ^"■' r' ) . ' / , K 'iff ^ ■ V f \.' :’ jP^ , fc . :!i *'\U :■ > «.' r i ■u'f ^ ' '''■ £-0 I - f ■ !?7qrt:- 5PT “ »’ J J „ :>:i' ' t ■■- •'-' * ',■ ' 'i t ' ' ' • * ■ , ■■■> - * .;. '?*■ u‘ ow;? ■, W -^' * ii . r ' " ' ^ rf'.V '» ■j'j . \ ;,- : j -> .. ...•.• 'SCrrt^T.." i '■ i •■' ■>:’■• r.rss • ■ J. .. 3 }! Vi ! f ** ** f i. 1 ;.r ^CC '■ -36- seedlings grown at a temperature of 20®C. , a condition opposite to that occurring in shoots may be observed. In roots the greatest dry weights occurred in seedlings grown in a soil 5 per cent saturated and in a relative humidity of 30 per cent, while in shoots the lowest dry weight occurred under these same conditions. The only consistent differences in the mean dry weights in the roots of seedlings, grown at this temperature and grown under the same conditions of soil moisture, occurred where a soil 5 per cent saturated was employed. But even there, the value by which the seedlings grown in the lowest relative humidity exceed the seedlings grown in the highest relative humidity gives odds against the difference being due to chance of less than 20 to 1. In the seedlings grown at an atmospheric temperature of 30® C., the maximum dry weight occurred under con- ditions of medium soil moisture. The differences in either di- rection are too small to be of much significance. Table VII. Mean dry weights of roots of seedlings the shoots of which were maintained at a temperature of 20*^0. Soil R. humidity Mean wt. Standard Coefficient of moisture (per cent) (in eg.) deviation variability (per cent saturation) 5 20 60 30 4.7± .15 1.09± .10 23. ,2± 2.32 60 4.4± .10 .72t .07 16. ,4t 1.58 90 3.9± .13 .92± .09 23, ,6± 2.40 30 4.3i .12 .95t .09 22, .It 2.13 60 4.0± .11 .96± .08 24. ,0i 2.33 90 4.2± .12 .89± .08 21, ,2t 2.11 30 4.oi .09 .71± .06 17. ,7± 1.68 60 4. it .12 .97± .09 23. 2.28 90 3.8± .09 .71± .06 18. .7t 1.76 ► ' 4* V 4. 1 ? ■; •t 'I' *■ ■''. - ' i . ®' *1. *■•'■• .’ia J ' a / ' i. Lr>u'-i- f- . >’ ■' •t \ • r. ^ i'" 1 OV' - I I ■ ' ki“* C . •■ f ' -t' . ‘ :i-i .1 * . I • f • .tinf TUtStint^ -37- Table VIII. Mean dry weights of roots of seedlings, the shoots of which were maintained at a temperature of 30° C. Soil R. humidity Mean wt . Standard Coefficient of moisture (per cent) (in ( ) deviation variability (per cent saturation) 5 30 3.9i .14 1.10± .10 28. 2± 2.78 60 3.8l .10 .74± .07 19. 5i 1.85 90 4.2± .05 .36^ .03 8.6± .83 20 30 4.2t 4.1* .11 .83± .08 19. 8i 1.88 60 .08 .63± .06 15. 4t 1.45 90 4.2± .07 .49± .05 11.71 1.16 60 30 3.9t .07 .54± .05 13. 8± 1.32 60 3.6j .06 .45± .04 12. 5J 1.17 90 3.7* .10 .71± .07 19.2* 1.97 Table IX. Mean weights of seeds from which the seed- lings grown at 20°C. were obtained. Soil R. humidity Mean wt. Standard Coefficient moisture (per cent) (in ( 3g. ) deviation variability (per cent saturation) 5 30 44. Oi 1.09 8.09i .77 18. 3± 1.80 60 43. 0± . 66 5.07± .47 11, et 1.13 90 46. 0± 1.01 7.77± .71 16. 9± 1.73 20 30 47. 6± .97 7.30± .68 15. 3± 1.47 60 46. 7± 1.07 8.25± .76 17. 7t 1.67 90 47. Oi .70 5.20i .49 11. 1± 1.08 60 30 44. 3± .78 6.03*^ .55 13. 6± 1.27 60 47. Oi 1102 7.82± .72 16. 6i 1.55 90 46.6- .94 7.61± .66 16. 3± 1.53 On examination of Tables IX and X it may be observed that the differences occurring between any two means in seed weights are small. The greatest differences in mean weights of seeds, from which the seedlings grown under the different en- vironments were obtained, amounts to 7~ 1.6 and 1.3. In both cases the differences give odds of less than 25 to 1. Since -38- these odds are rather small to be significant, the differences in the rates of elongation cannot be accounted for through differ- ences in the weights of the seeds employed. Table X. Mean weights of seeds from which the seed- lings grown at • 0 0 0 to ' were obtained Soil R. humidity Mean wt . Standard Coefficient ( moisture (per cent saturation) (per cent) (in eg.) deviation 9 ^ L variability 5 30 42- 1. 3 9.71 .90 23.11 2.22 60 45± . 96 7 . 4 I .68 16. 4± 1.55 90 471 . 69 5.3l ,49 11. 3 I 1.09 20 30 491 . 96 7.4i .68 15.1- 1.42 60 46i . 96 7.41 .68 16. li 1.52 90 45l . 84 6.ll .69 13. 6± 1.34 60 30 45- . 78 5.91 .55 13. ll 1.25 60 44± . 83 6 . 4 I .59 14.51 1.36 90 47l 1. 21 8.6l .85 18.21 1.87 Tables XI and XII furnish the mean total increments of elongation in the shoots of seedlings grown under the differ- ent conditions of temperature, soil moisture and relative humid- ity employed. On examination of the tables it may be found that, with but one exception, the seedlings grown in a soil moisture of 5 per cent saturation made smaller total increments than those grown in the higher soil moistures. The differences in every case, excepting the one referred to, are significant. Between the seedlings grown in a soil moisture of 20 per cent and those grown in a soil moisture of 60 per cent saturation j the only significant differences may be found in t^liose grown at a temperature of 20 C. and in a relative humidity of 60 per cent. In this instance^ the difference is 59^ 6.76. chK: .•.i.-:; •;. ;^c ;;c \ti h 1 t'i '. ./ .f'ujyi 1 i it 'i. .. I fr. » ' . '5,. • ii J ■ ••i’..* .r>ii "fNrlis*/?© iVi.7 ; .. ?<§.. . i. :::i t%* ri„ V. \ — V w V c. w ri ■ ' ' w ■ >1 0 1 ^ , ,u • .• i " ' ' ' 4 • . „ ... V , ^ - J.- ,1- 1 -*lVX'i:'4't ‘ ?i'S' *tf..*>KV' u’r */: ;., ■ -i?i(v.i,.. ' ^jv,.i, tii3.n^''5. ■l'^v;: ‘-,J >.• .-V /'-'■ • ■ -■ :• ,s »•' tv' t o’ uf i»;' Xi : -V J t-po:.:" ;T_ •. ; T'fi ~i' , -j ■ t‘^S-^a|-.''V3V'w .tx* .;! 1 - " ' *• * , f ' ^ ,.i; 'iu^ *3 ■ • ■* \ * * 4* . . 'PP* ".'L" ' % ■ -39- Differences brought about by relative humidity occur in a few cases. In Table Xl, it may be observed that in a soil moisture of 20 per cent saturation the seedlings grown in a relative humidity of 60 per cent made an increment significantly smaller than those grown in relative humidities of either 30 per cent or 90 per cent. In the same table, but in a soil 60 per cent saturatid^the seedlings grown in a relative humidity of 60 per cent exceeded those grown in a relative humidity of 30 per cent by 42^ 7.82. In this case^the odds that the difference is not due to pure chance are about 100 to 1. In Table XII a signifi- cant increase brought about by an increase in the relative humid- ity may be found in the seedlings grown in a soil moisture of 5 per cent saturation. The difference referred to occurs between those grown in relative humidities of 30 per cent and 60 per cent ^ Table XI. Mean total increments of elongation in shoots maintained at a temperature of 20® C. Soil R . humiditv Mean incre- Standard Coefficient of moisture (per cent) ment (in mm. ) deviation variability (per cent saturation) 5 30 2471 2.70 20. 0l 1.91 8.li .77 60 262- 3.40 25. 7± 2.40 9.8± .92 90 2311 6.96 53.61 4.93 23.21 2.42 20 30 3011 4.39 33.21 3.12 11. ol 1.03 60 2571 5.61 43.11 3.96 16.81 1.58 90 3081 5.61 41.61 3.96 13.51 1.31 60 30 2741 6.85 52.71 4.85 19. 2± 1.83 60 3161 3.78 29. ll 2. 66 9.2l .84 90 306* 5.50 42.31 3.89 13. 8± 1.29 respectively. The odds in this case, according to Wood ( 'll), approach 1000 to 1. ' “' ' '. ' ■*. ■«<( '• ■• <■ «■ V' ■ . rrl ti. I',' . - • /AluX'?': . Y': ■ ■ i .. -Xi.-'x-a .. Ltup.6TX. 1 (*' ' ' ' < SAitf*? iXIC-f* *•-'■'•; ‘'’' C . ;vv i:^*.'.:uo '^|i' ■ t 1 i -LiiiG-tJf- X- rt- ., ... •* . Xv . z- ■■ ; ‘ . ' • V ' ' ' '-. ' X ' *1 J*; . . r 3 j-.-i L ^ . - ''^ ' .u’.'.'.' l,., J • '-■ ' ,''i j Cv :) j. j "if ■ &vX;/<; ■ . •« .: XL' i /.\v; . .. I?i.l.ci'x..., . .. : .. L.. ,;r. •' .w .. ^ . '•■ f .'i; i 'L.‘. • w v' . .L * X .• ;ti r.i .■-i-iiV'-? ..;-*;'5 ■ \litt \*:.. . -, . ■ ' "’■ ' Z' ' ■ ^ r*;-.''. (.v.ti, ■.».,••: \rj v f,'.. i .: ;. 1 r: . <... ^*'. . -'*■■ ' Xa^io;’ %' '" j'i i.fc* ■ £i'^. . ^5(IU i . •- */ f/t i^dZV ii.. '■“uy -■.>.>■ V‘.; '•f. '■ fva-'"'l’^''.-' .,.»« Li , :^>fi,' -V '■(=/ ' *■ ’■ . r 44 < ^ ' H '■' •••■ \ X i . ..li .i *jCi:VV X !• i < ..Ji’&tto >■■_ V" . C>*% i' t. ■L, .. i. *J , /**'■>,■. M'.' 0 ; /' > .1 s , j 1 " ■A' * ' 4 ?. f >“ .-• K, . V -y '* 4 . li.. ■; • ... a ' 06 ol ,.^ ;ofr 4 ' . ' < •' , 'i'’* ■ • i ■ ‘ ' .•(i 'l-L* • |f ‘Uij ‘ /> *« La 10 J > . **»• - ** I .' iV .’Sttefc-x -40- Table XII. Mean total increments of elongation in shoots maintained in a temperature of 2>0^C. Soil R. humidity Mean incre- Standard Coefficient of moisture (per cent) (per cent saturation) ment (in mm. ) deviation variability 5 30 3331 4.28 32. 9± 3.02 14.1* 1.32 60 2741 4.40 33. 8^ 3.10 13. 3 I 1.15 90 2561 3.68 27. 3t 2.60 10.7* 1.04 20 30 3151 3.55 27. 4 I 2.51 8.7* .79 60 3061 4.13 31.81 2.92 10.4* .96 90 2881 6.22 45. 2 I 4.40 15.71 1.56 60 30 320l 3.88 29. 3t 2.74 9.1* .85 60 3001 3.92 30. 2t 2.77 10. ll .93 10.61 1.06 90 3141 4.70 33.4* 3.32 Mention may here be made of the general ( sharacter of the root systems found - on the seedlings grown in silica sand of different moisture contents. No actual dataare available, but striking differences in the length and the extent of the branch- ing in the root systems were observed. Seedlings grown in a sand 5 per cent saturated possessed a short main root with many laterals. Those grown in a sand 60 per cent saturated possessed a long main root with few laterals. Those grown in a sand 20 per cent saturated possessed roots occupying a position, in respect to character, intermediate between the other two. In the seedlings of the last group^the main roots were moderately long and the lateral roots more numerous than in those grown in a sand 60 per cent saturated. 3.. Growth of Seedlings in Darkness Alternating with Light. The data presented in Tables XIII and XIV give the -41- inorernents of elongation and the total fresh weights in bean seedlings that were subjected to a daily illumination of 12 hours. On inspection of the data it may be found that the mean 12-hour increments are the same. In respect to fresh weight, the value for the seedlings grown in a relative humidity of 90 per cent is the higher, but it exceeds the value for the seedlings grown in a relative humidity of 30 per cent by only .09- .063. It is evident that this difference is too small to be significant. From the data presented in these tables it appears that, under the conditions of the experiment in question, a low relative humidity is as favorable as a high relative humidity in the formation of fresh material in shoots of bean seedlings. Table XIII. Mean 13-hour increments of elongation in shoots maintained in a temperature of 30° C. Soil R. humidity Mean incre- Standard Coefficient of moisture (per cent) ments (in mm.) deviation variability (per cent saturation) 20 30 17,21: .19 1.44t .13 8.4± .77 90 17. 2t .29 2.14t .20 12.4±1.20 Table XIV. Mean fresh weight of shoots maintained in a temperature of 30° C. Soil R. humidity Mean weights Standard Coefficient of meisture (per cant) (in grams) deviation variability (per cent saturation) 30 30 2.15t .041 .32t .039 14.91: 1.40 90 2.24i .050 .37± .035 16.61 1;02 On comparing the values in these tables with the corresponding values for the seedlings grown in continuous darkness, significant differences are found. In the rate of ■ I J ...r oni '■’^liL' 1 !t .9 - •>■ «r' 2 ^--! ^ -^l: . ' • . V r . ,i, , _. 7 , , Ov' •^''^ 'y-''- ^’*-'" * ; £i/ . . ,..IOf-' i I w'^.r' \ ' ' ' .t 'v “X • 'i^r>V. OJ- Li:, t’l jkp • . L uoilo -i rtx ■f (^'; : r :r- ^(.*-0 ■i!jq O£ .TO-, .-. •*iV::.wX-jt’'..i<;.ni. •• o^SfiT'-'. liV ’ ■ ,'^'l ni 1 ' r ■ :i l. i . u 'I 5 I £ t 1 ' "'iai' f’ • > -ji cyiSv-i.,.-':' L'...tjV ■■'f Jj'.' .■•' •;"'^ifi *' ' . ■■■ *w : 1 ' . '■-■ Xv '■ '^.. c-' uj. • a . i: >^V *;* V • 1 L . 'mA •fk'iiTe 1 ; 1 I, -. -CiT.. w' fe. ,i. » . ilJ £•. ’ll ' G • ^ f/<'.. » ^ ft I X *4 rji J& }tiv> XO'i -v '-.J, •'■)-" V. / '■ , .. ..;,{i^ iU v;? ; ! i. •; .’^ l ■ .,.. /. i.-v’ ■>'. ■:* *■■ ■■■- 5 -.i* ;.i ^ ”■ ■'’ ■■ ..V ' ® \i : u :^ti■ its. ' .'■■■ ■. ■:.j ■ ..1 '''I.;- 'f*.r ■■■ • *':c.'T. u- . ;f.- ;.. ■■■■ y-> i- .. /jt l - ,'d i. ii '"> i; ; ' ; ■' ■■ ■ ^ .i. X 1 'i V ; ' t, , , (^. *• "' i.J V ■ . 1 . '- r .'V ■ r;. . -X r V' - 4 > >'. - . ., i , V - V «■ t n,#. } — . --V u ' -'U ■ '0 ■ '■ '(Vi '•^ . '■■/ r ^7 ,, '.."'il 1 i^J it 'S ir\. * f , o<: •V “T ' . -V ■?* VL ■ ■>’v'vtr. ■ (-.•‘yv ’ ’ll t.' -i« . Xl'.r V i>^ - '4* -M . t-; . ^•. I \r » ■ ♦ i. TT iT *. ■ til: ^ji' Kis^y 'i‘ .K' * ■■'■ •> r' • ■ , ■ **,.'■■ ^ " '*- ■ : ■■ \‘'l A **s^T»'»?r'SSr. -42- elongation, the seedlings grown in continuous darkness exceeded those grown in part time illumination by values that give odds not of upwards of 1000 to 1 that the differences are^due to pure chance. In respect to fresh weight, the only difference giving odds above 30 to 1 occurs in the seedlings grown in a relative humidity of 30 per cent. Table XV. Mean total increments of elongation in shoots maintained in a temperature of 30®C. Soil R. humidity Mean incre- Standard Coefficient of moisture (per cent) ment (in mm.) deviation variability (per cent saturation) 20 30 2191 2.41 18. 5^ 1.70 8.4t .77 90 241^ 3.50 25. 9± 2.48 10. 7± 1.03 In Table XV the difference in the mean total increments of elongation in the illuminated shoots is shown. The differ- ence occurring is 22^ 4.25. Considering the probable error, this furnishes odds of about 75 to 1 that the difference is not due to pure chance. Since these odds are above the minimum accepted for certainty, this difference may be considered signi- ficant. The total increments of elongation, as given in Table XV, are decidedly smaller than the corresponding ones in Table XII. In the two relative humidities (30 per cent and 90 per cent) the differences occurring are 100- 4.23 and 47i 7.14, respective- ly. In the former case, the odds that the difference is not due to chance are upwards of 1,000,000 to 1; in the latter casej up- wards of 500 to 1. These odds are sufficiently great to be sig- nificant. N , ■ ), ■ :' ‘ „ lo -c;::..!’ -. w'iX" - n r.~ . '.. . :"(. r ^ ^ ♦«** s^’.i T ^ j^Y ♦.<*,' Ar4' 'C-‘ . vi no.i .^ .: V-'.i. (',. .'• " 1 \ ' ,' 'V 1 ■ . J ' O' ,5 ■\ V . • • . ■ ■ .'X -. . •■ 1 ■ ' ■ I- ■ - • . ‘ . « . . . - — -» • '/ s7< ,( ♦- •’ . 'r ’ ■' ^ W’ r y 4 -. ' a.-l-« wi ‘i) 3^ - -1 ' ■ i ‘ t" ► * xo :ax . y -• -'i; ■; „L J4,.. c* A , ar . 'i. .1-4.;-.; x;, f • ' '■ '• ■ • ' V i- ■ ■ =*t ti. <: ■I 4^.) CV xx'^'Y? -%o ' ' . , . . . j- ^ ' *r , • . ' ' 'r^'J-'j'. f. -■ 4 1 ”■ ■' O' fj*';’ ;..- . ^ ;%x i ^ ■ j 1 ;/I*s • - " - ■•; '^' ■ Til , »' , tf t’ •? X<-; .•: r i‘i cv-tfo x1. K«0 'l.t/-'' p ' ..''.f.'vjic-i ' {» i'... n I a: ;-S^C v^; • •' '. ) ■ ■«; , .. i >:..i.^ ; w,t\ -S‘\ j .' j *L; 7. . , ’ ^ . ;; Xi/aCfw ' <^V4V , ‘ -4, "4 u*ii ■ . ^ ‘ n v.i . ' ■ ■ j • tVK ■ 7 1*;* 1','. T .L^;' " >i 'I V ^ . .* i *• i I ^,..1 ♦■^r .ir'i ;f ' . ’ \- "^ 'I i ' f ^^ 4 . U •*> ,j ,4'*. d \ ;r£^^lo^€. i- ;' uv : lih^,iix ^ eifi.-' r.:. '.•■■ ^ ■ \ ■'' I i'itii t T-.*’ li^Ei' r iC y. ^ iC^DJ i .' (. 5t'* . ■‘'Ji-'f ,j-f; ''‘v.f 9. ♦- » j- ■ ' 1-'’ ; . ■ ,>v i ;^4Txn’' i - :-P^ M- r- ♦ H, 7 '■ V' . . f I* ‘ ’: ' M O.lj, h:i j . . 4*. :' •■ '.'■ A, .- V', • tyU- ■. :'■ > , eW4 ; " H’- ...f : .( .'■» ■■ ,f 1 1' #iV'^r .'■'"■'.j'”' ' ■ • •t t . « • < ' J » «i o . -• ' 1 \ ) ■ ■■:^^ lU^'. . . ■ ...v: eXi mr ^ ■ . .1 " '.(■J . - .^. O'.' •'S ■■'’^ 9 rf‘;- i - ^ •: ' /i.i'iv'n ;U'- » .. ) 7 .t^ nt^, ',:' ••■ .7,-c r^;;t),::j I 0 ihli -45- ences between the values given in Tables XVI, XVII and XVIII and the corresponding values in Tables VI, VIII and X do not appear. The seedlings grown in darkness alternating with light differed in their characters from those grown in continuous dark- ness. One of the chief differences occurred in leaf development. The leaves of the seedlings maintained in darkness remained small and in many cases did not unfold. The leaves of the seedlings grown in darkness alternated with light unfolded early, and at the conclusion of the experiment had attained a size several times that of the leaves in the etiolated seedlings. Another important difference between these two groups of seedlings was in color. The seedlings grown in darkness alternated with light developed a deep green color, while those grown in continuous darkness remained pale yellow. This greening in the seedlings illximinated part time could be observed soon after their exposure to light, and at the end of the first day the primary leaves exhibited the color characterizing normal, illuminated pllants. In addition to the data presented In the previous tables, data were obtained on the amounts of water given off by the seedlings during the period of observation. In the present paper these data have been omitted, owing to plans to present them in a separate paper in the near future. The results of our experiments briefly summarized show: (1) that only in a soil 5 per cent saturated is there a significant increase in the rate of elongation brought about by -46- an increase in the relative humidity; (2) that as the soil water is increased from 5 per cent saturation to 20 per cent saturation a significant increase in the rate of elongation in etiolated shoots occurs; (3) that, in general, the higher the moisture supply, either in the atmosphere or in the soil, the lower is the per cent of dry matter in the plant; (4) that changes in the amount of soil water from 5 per cent to 60 per cent satura- tion do not bring about significant changes in the relation be- tween the dry weights of root and shoot^ (5) that light retards growth. VII. DISCUSSION. Already, attention has been called to the fact that the results obtained on growth in relation to relative humidity, in this investigation, do not accord with the results obtained in some of the previous investigations. The data furnished by these other investigators do not allow of an explanation of the discrepancies. If an exact knowledge of the conditions under which these investigators worked were known^it is probable that these differences, in part at least, could be accounted for. It is true that plants of all species do not agree in their response to every environmenteil condition. It is possible that plants of one species may react more favorably to a high relative humidity than to a low one and that plants of another species, under the same conditions of environment, may react more favorably to a low relative humidity than to a high one. I-* '.»'-*i-5* OCTn- IS. -- ••• v'^-V H)^’*^, J . /»•" ^,*^0 Ml ■ / ... fl : ■ ' iwit - ' ■■.' . !« ' . "'-». ^ ,;r .>».V'*^^®*J"V "■'’' ■' - ■'"' 'A';, K .L ’V^- % :,\ ., ■■ ‘ ■ :. i,^w • At \0 I - 47 - A definite answer to this question, however, awaits future in- vestigation. Imperfect control of the environmental, conditions in the previous investigations are responsible, in a large measure, for the differences obtained. In some oases contribu- ting environmental factors have been entirely overlooked and were the data presented^obtained from plants or seedlings grown under from conditions widely different ^ those indicated. In previous researches on growth in relation to en- vironmental conditions, with but few exceptions the cultures under observation have comprised but small numbers of individuals. In only a few cases has the number exceeded ten and in many cases the number employed has been less than five. It has been pointed out by recent workers that conclusions based on such small samples may be entirely erroneous. It is known that plants of the same species, under the same conditions of environ- ment, show wide variations in the rate of elongation. The plants or seedlings exhibiting the highest growth rate, among those in an unfavorable environment, may make more rapid growth than the plants or seedlings exhibiting the lowest growth rate among those in a favorable environment. If, in comparing two environments in respect to their effect upon growth, the plants selected should fall in the classes referred to, it is obvious that the conclusions drawn would be misleading. Thus, it may be seen that conclusions drawn from few individuals or from few cultures may lead to grave error. Considering the great com- plexity in the factors conditioning the results, and the absence -48- I of full appreciation of these, lack of consistency in the con- clusions reached by earlier investigators is to be expected. The results of Sorauer ('80), Reinitzer ('81), Reinke ('76), Wollny (*98), Anderson ('94), Darwin ('93), Clark ('78), Tsclaplowitz ('86) and Eberhardt ('03) apparently agree, only in part, with the results obtained in the present investigation. While some of these investigators secured very marked advantages in favor of the higher relative humidities, others secured only a slight balance in that direction. A definite explanation for these differences in growth cannot be given. It has been stated already that there is a possibility of plants of different species responding differently to a given set of conditions. By some it may be suggested that the great diversity of plants employed, in the experiments referred to, will account for the discrepan- cies. There is, however, no experimental evidence to lend support to such a view. The small differences shown in the tables presented by some of these investigators are no greater than the differences which, in this discussion, have been con- sidered insignificant. In addition, the number of cultures employed in the present investigation greatly exceeds the number employed in any of the investigations referred to. In fact, in some oases the conclusions reached by former investigators were based upon the growth of a single individual. 'This renders their differences less significant than if larger numbers had been employed. Owing to the use of such small numbers, it — ■ ■ — /’'i- U"’ ; .i .:...k^;C . ^ '.V . VC :■ ;.U,A-; *-■ . i'.'. • ■, /I .L - i*i T,'." I'i .^a,-" ■i , i ; IC' .’f ^ -:^vn j|> ^ % i» ^ • - ' -• ►»• V t»- V ':'■ '" o ■SO^C, a. . .! l-i;' :.e':oL.pT " V. ;A ; 4 1 V. /•■ •-. »•>... .n . f. ... . , -49- raay be that the differences obtained are only chance differences and that, if the experiments were repeated, the lower relative humidity would be equally as favorable to growth as the higher relative humidity. On the other hand, the results obtained by Schaible COl) agree with the results obtained, in the present investiga- tion, on seedlings grown in a sand high in water content. If Vesque and Viet (’81) had based their conclusiohs upon the average growth of all individuals grown, rather than upon the best individ- ual from each group, their conclusions would have agreed very well with those of Schaible. Since the dry air admitted to the plant chambers was not controlled, in the investigations mentioned, it is not un- likely that in some cases the relative humidity reached a value much lower than the lowest employed in the present investigation. Where very marked differences in the growth rate between seedlings grown in a dry atmosphere and seedlings grown in a moist atmos- phere occurred, as in the investigations of Reinitzer (’81), the air on entering the plant chamber was passed through tubes con- taining pumice stone moistened with sulphuric acid. Under such conditions, the relative humidity of the air entering the plant chamber undoubtedly reached a value below 30 per cent. This very low relative humidity, possibly combined with unfavorable conditions of soil moisture, may assist in accounting for the wide differences in the growth rates recorded. 5 fc;,. -r''' •m 'iT«^,,i - ■ ■ ■ ■* V. * " ' ; , ,.; . /,'j 3 ' \ -ff. ! Mi"-’ '^:J!'^ '• 'u' ' *'£ -50- The data presented in the previous section of this paper bring out the fact that in a study of growth in relation to relative humidity soil moisture must be considered. In these experiments, a silica sand 20 per cent saturated has proved to be capable of supplying water to seedlings, growing in a relative humidity of 30 per cent, as r^idly as required for maximum growth. This confirms the conclusions reached by Hellriegel ('83) who recognized that the amount of water given off by the plant exerted no retarding influence upon the growth rate, so long as the amount of water in the soil was maintained within favor- able limits. The observation of Hellriegel ('69), Fittbogen (•73), Sorauer ('73), Wollny ('88, '92, *97), Gain ('92, *95, (96), Shroeder ('96), Mayer ('98), Tucker and Seelhorst ('98), Pagnoul ('99), Seelhorst ('00), Prianishnikov ('00), Seelhorst and Freckmann ('03), Hunger ('06), Preul ('08), Harris ('14), Kies- selbaoh ('15), Shine ('20) and others are not at variance with this view. Although the above investigators make no mention of relative humidity in their investigations, evidence is presented in favor of the view that soil moisture is a very important factor in determining growth rate in plants. Burkholder ('19) has shown that plants of the common bean, affected by the dry root- rot, are able to carry on their normal functions if an abundance of water is present in the soil. If, however, the soil moisture decreases, the few remaining roots are unable to supply the plant with the requisite amount of water and the growth rate decreases accordingly. The data presented in this .*» i.-.t * V\ If a: ' T e . t-' V i''*. '.C, '! ii. f 'i 70 ^ .. i' ■ .' . .. Vv i y^ie,! o^* :le'i i:. t.. i^i'.;'i:i'Z- ni\S\L>.:r r- • ' •'■ 1 :,: tIo T ^1* ‘^v 1 o •■ ' T'" •; , ---;1 ■ : V ‘k’ci ' •■ j : ■ ■ „ . - ft . V ' h’", ' ■■ • rxZ •: *i:r ‘ •. .>:i i-sJ'nip,’ '•Vwyv '. •: I ,. t vr* r'* •Oi > 6414 ■ . ( , I . -f r* ”1 * •' i..r' t ofcj. :' n i-: . .. ', ,. • 'V ■ » • ' , ' ). » ,’■ ‘ ' '. /r* ov, -vdiiiV ; J-. 0 (j:y-^}''t^i ,e .'..a ' ’ •■^ ci: c'?r-li 6 *‘ !'■ ’- .■ / ‘■• * ' *, i-i-’ *•' .. i ‘L'l , ( ;■. • ■ ' . T. . -• j V, , 4 :: P .■i * .'. • . . > # I ' ' ' .' .' .j* t ■ ' ^ * i‘ * ' ic* . -•>-'! -• ^ < i I 'll ' •£;': Ypa " ” no V^^ ^4a ',-:i ■■ ' V.-, .IlT a i> . Bv« .>r ‘XO.^Cjii ^ v' .4 I'to. 4 .. urf^' ‘"■'■''f ■. - V '‘i- ■ ■ 7 ->: ■ ■ . 4 "' ' , • i j y _ . ‘ ' ' ' Ov ■ ."-t ’:- :-- 1 V ns/iffl: •: •-.:(*! ; Cf'i- •6 j:u '■' iaC'.ifiW .’1*. w:’t,:'r..; o/:Vv .■. in* 3 i .w ' O': ; * JJiH'' -51- paper show that in a sand only 5 per cent saturated the avail- able water is not present in sufficient amounts to supply the needs of the plant for maximum growth. Under such conditions of soil moisture, a higher growth rate would be expected in the presence of a high relative humidity than in the presence of a low relative humidity. This occurred in the present investiga- tion. From these considerations it seems probable that soil moisture was a limiting factor (Blackman, *05) in at least some of the investigations referred to. The observations of Kraus (*95), Lock (’04) and Smith (’06), agree with those of Reinitzer (’81), Smith (’06) and Lock (’04) attributed to relative humidity a great role in determining the growth rate in shoots of Dendro calamus. This may have been warranted, but the data on growth in bean seed- lings presented in this paper show that in doing so soil moisture must receive due consideration. The evidence brought forth in Table I suggests that the relation between relative humidity and plant growth is more complex than these authors have in- dicated. This complexity in the environmental relations of plants growing in nature is further brought out by the observa- tions of Douglas (’06), Greeley (’20), Maxwell (’96), Prantl (’73), Stebler (’78) and others. That relative humidity, as a factor influencing the growth rate, has been greatly overestimated and that soil mois- ture^ in this respect, has been greatly underestimated is supported '•K T” ■» • 7 I l:(i.,,\‘- <■ ..r *X:: ..C .-’*•> •<. Jt.''. ‘ V/ ^ (,J- ; , *v ■ 1, ,^- ' £l ‘iq ; .. . . - " r ■■; ,'> i’ ,■. ' • I ; 1 CJ r.t 4 SI 4. ■I? .* . Si : ••I •'. ■ ■ w II J IJ * 1. •:'M“t; Juicf' ^ ■■ . :)^v ^ .■ '■ »■ liT.;'. t - , j , < . ' .• ■: <■■ *.o f'' '. ■» i: • •.>-!; •‘.i - .- ll.q) ■' c : :i xisiitSS .'. v: . 7^ . >'.”■ '■ !*• ■ X > X I :<5£Leoo'rV:9i 'tj' -• -i ■ f 4 • ■• • . . rrr'. ■;:' . .!C ■:* fWt-a’ifilhxI'io'T ■•-■,• ‘i n >. *.. ::• :■!. ‘tj?:r. : .e ' , iOC. SU : . •l'': •ci v 'vV’.u .VI - r' ^vl 'iCfjfJ .-.> ».v.- ^W :?i. - . ■'' 3'i. .' , /' ‘ I *•■',■ ' . • ' 't .' ' ;p <>i . jvjcj*? - SK-iit'fj - ‘ ,?X3€ ■ ■l .,’>t *- .. i-i. I* J >' » 4> V .'•I f .» .. .* '-I ' i . t ■ > A 0 * ■ i ^ ^r*<- * i 4 V, • -- » t' 0 ,X'. p{ti7. ■ ^ ^:7t. .,>vvc'-' air •> ( * I ^ ^ « :r •' ..jCoft 7 '-,: . . ixo-r-iv^f -.1 'a.:r.i v St cv . l-' ■ , 7 -52- by the conclusions reached by Shibata. A curve representing the growth rate in shoots of Dendrocalamus^ as observed by him, shows no relation to the corresponding curve for relative humid- ity. While the relative humidity, at times, reached a low value, the water required was present in the soil in sufficient amounts to supply the needs of the plants, without inducing a depression in the growth rate. The relation of growth rate to soil moisture, as shown in Tables I and II ^confirms the conclusions reached by Pearson (’18), Douglas ('09, ’14), Kelsick (’18), Kirkwood (’14), Bogus (’05), and Taylor and Downing (’17), Pearson states, "The im- portant fact pointed out by this study, however, is that it is the April and May precipitation which is most .important in deter- mining the amount of height^growth and presumably the moisture content of the soil during the period when height growth takes place". Similar conclusions were reached by the remaining authors. With respect to the effect of soil moisture upon the weight of material produced in root and in shoot, the results given in Tables III - VIII and XV - XVII in this paper agree only in part with those of Hellriegel (’69), Sorauer (’73), Gain (’92, ’95, ’96), Shroeder (’96), Mayer (’98), Wollny (’98), Tucker and Seelhorst (’98), Pagnoul (’00), Seelhorst and Freck- mann (’03), Bunger (’06), Preul (’08), Seelhorst and Kizymowski (’10) and Shive (’20). The above authors seem to agree in hav- ing observed that from an increase in the soil moisture, in- creases in the fresh and dry weights of the shoot and a decrease -53- in the dry weight of the root result. Tucker and Seelhorst (•98) state •’Die Ausbildung der oberirdischen Pflanzensubstanz der Haferpflanze nahm mit steigendem Wassergehalt zu; bei den Wurzeln war das Umgek^rte der Fall. Bei einem ger ingen Wasser- gehalt des Bodens trat die relativ gr6sste Ausbildung der Wurz- eln die relative geringste der oberirdischen Masse ein”. Their data' indicate increases in the weight of plant substance with increases in the soil moisture, until the soil reaches a point where it is from 60 per cent to 90 per cent saturated. Omitting the probable error, the data furnished lim the tables referred to confirm, in a general way, the results obtained by these authors. However, when consideration is given this error, these d data ir^oate no significant increases in the weights of the plants, beyond a soil moisture of 30 per cent saturation. It must not be forgotten that in the investigations already referred to, the plants were grown for a longer period than were those in the present investigation. The wide difference in the stage of development at the time of analysis may account for the dis- crepancies noted. The absence of light in the plant chambers employed, as indicated, and differences in temperature and rela- tive humidity may be important factors for consideration in this connection. A similar explanation to that of the former may be suggested for the results obtained by Polle (’10) on seedlings of wheat and barley, which agree with those obtained in the present investigation. With respect to the relation between fresh and dry Crt iiA' -!3 9 ’^’% * V i ii4 *^- v c»fl ■■ t ^ ; *. Q . r \ ■'.^ .V. ',; ;, ■' -^ -A ., . r:KAi’ sfer , /.' " ■ ■■ 4 ' •■ “ r, ' " ' ses U ■' "■ i, it:!V'^cnil(ror. 6 i' , " , ■ * ' '• ^ 'i* / A_'^Vj 1 ” ^ 'i ' ' '■"” ' ^' ' 'ii ‘ '' '^< 4 !!^'* 3 ^i' ■ ''■ ’ , ' 4 '. *' '• /*■«' i 4 ■ j ' iW^ I ‘‘ _€ bl ’.*^. ' ,i‘,' ' : . ,■ P ’ I /'■*••» ',' V . ■/ y " ^'" ' ]j* ^ * -■ "-"“ ya^ ,«^ ^ :'r '•>>'•■ '■ _ , .cropfeetfl m ' ' ' ','v®,;' . 'V. ■■ ,- ~ 44 it 4 . ■^Tiitik •■^' ... Jli; ' •> '^ . i ■• lA*_. Ij' j ■'■ fel *«. ‘‘**^*'' a^,Tim iMi fW i^ yj I *ri i t -ie Kyj wqpk ’, > M a>^ r- me - wJi •. -54- weights in shoots of seedlings grown under different conditions of moisture, the results presented in Tables V, VI and XVI jtiDEjt accord with the results obtained by previous investigators. Sorauer ('81), Gain ('95), Wollny ('98), Pagnoul ('99) and Prianishnikov ('00) observed that as the per cent of water in the soil was increased the per cent of dry matter in the plants decreased. Their results, as reported, are consistent and in some cases marked differences were obtained. Some slight in- consistencies are shown in Tables V and VI, but on the whole a distinct relation between the amount of water present in the soil or in the atmosphere and the per cent of dry matter present in the plant exists. The difference is more striking in the seedlings grown under part time illumination than in the seed- lings grown 4n continuous darkness. The observations on the illuminated seedlings agree more closely, as would be expected, with the observations of the investigators mentioned. The higher percentage of dry matter occurring in the seedlings grown under the less favorable moisture conditions are due, undoubtedly, to a greater development of strengthening tissue, as demonstrated by Kohl (» 86) and Wollny ('98). It has been shown that soil moisture and relative humidity play a part in determining the total increment of elonga- tion in plant shoots. The data presented in Tables II and III indicate that a soil very low in moisture provides less favorable conditions for longitudinal growth in plant shoots than a soil -55- high in moisture. The single exception to this has already been noted. With this one eiiception, the increases in the td)tal increments occurring in soil moistures of 30 per cent saturation and 60 per cent si-turation, as shown in Tables XI and XII, are not unlike those obtained by Sorauer ('73), Hell- riegel ('83), Gain ('93), Wollny ('97), Seelhorst COO), Hunger ('06) and others. Their results differ from those presented in the tables referred to^ however, in that increases in total elongation were obtained in soil moistures much above 20 per cent saturation. It is true that in the present investigation soil moisture3between 30 per cent and 60 per cent saturation were not employed. It is, possible, therefore, that a soil moisture, intermediate between these two, would provide more favorable conditions for elongation in shoots than those em- ployed. A definite answer to this Awaits further invest igatioh. The fact that in the researches referred to the plants were grown in light, while the seedlings furnishing the data presented in the tables indicated were grown in darkness, may account for this discrepancy. With reference to the exception noted above close inspection of the tables suggests that this value does not truly in represent the total increment for the seedlings falling^that group. This wide difference is due possibly to chance. If this experiment were repeated fifty or a hundred times, it is probable that in eveyy case the value would approach more nearly 1; f. ■ ■ . ;.rva^,■■;Vi^ ,v^ . ; ■ •'■ .V '■' ::■ - -i t . , f: ' .'f e-rt0‘ . 1 H V? '4l *uVV *5 ,*'»• . {.L- L.f, ., ^ i 1 • ' ' ' t W. ' - ' -v' ^ •l\ ■ 1 -’ ; ' • •C '..,-.:-j > W \ A 1 ) /*' ■■• v; '1 -‘ s •>,0' :4^-' •■ •■;■ ::1' ' 1 -.' vf' ■ 7'’1 •« ■ V v'-^ i : ',tp- ' !; ,\ i'Hm ■■■.', ', vi '4(\‘ • » ' J.. . '. :, r:,.i V • :: ■' ' . :'r.-rj* i'>. , r,- V" \ '•) ■ -,.T J ‘9 -i I- J > ^ t '■ a;’.' u ■ J ' f, sv *. -■'. 1 • ' ''-V 1:. i io^:rL ■■ ; i'i Tv' *»■ , t . ?«t /■ J*' « . • *' Att '. 'v,[i i '. . . ' '^ • •*' * ’ if*Vt '.' ^•*^^ t ■ ' . ' ''^' . ;„ . )' „'.. ' ' -56- the values of the seedlings in the neighboring groups. In respect to the effeot of relative humidity on the total length of shoots, the researches of Reinitzer (’81), Wollny ('98), Eberhardt ('03, '04) and others are confirmed by certain of the data presented in this paper. The number of cases in which relative humidity has brought about a significant differ- ence in the total increment of elongation, however, is too small to place much reliance on relative humidity, within the limits of that commonly occurring in nature, being an important factor in determining the total length of plant shoots. In presenting the data, attention was called to the differenoes in the rate of elongation between the seedlings grown in darkness and those grown in part time illumination. As already indicated, the differences are very significant. Light decreased not only the rate of gro\7th, but also the total increment of growth made during the period of observation. This agrees with the conclusions reached by Prantl ('73), Sachs ('74), Stebler ('78), Barenetsky ('79), Godlewski ('91) and others. On the other hand, the observations of Meyer ('28), Maxwell ('96), Vog® ('15) and others do not accord with the results re- ported in this paper. In seedlings of sunflower, growing in the free air, Reinke ('76) observed that growth took place more rapidly by night than by day. Where relative humidity was main- tained constant, however, he observed a more rapid growh in light than in darkness. It is difficult to account for the : \' • m , ><: -i ^■: : V:-^ ,u .• C>~ .. . I - ( • ' / ' ' X >.■ ' '■...u '' K , J ^-5. ,- Aiv Vi'^i Ii''» ■■■>'' -' • _ ■ I I ' Y>'f-' I ' ■ K- t. \ 1 • ■ '« •* •«X* ' ■• ■ , . . • "^' 1 '*>■' . ’ i> « \ ‘ i^n -» li- . 1.5 ■i*: ..■. i:.' r« ;.■ '.-ic' *’ ‘ • • v )4 ^ 4 - 4 -i- : 5 ;, l*: ;.-*r ; ■:. I ■ ,. ^, ' - i. W ^ “A * J r \ " t: ' ' ■ ‘ ♦ V V ' •.. V • '* 11 -^ . \ '■' 5 ?.fr' ■ s '*• '■; • -V '. Jr' . : A . < / •^ ,.: .C.; Ts:\:i , . 4 ; ^ ;?.r, ' :. ' >11 '■£] ■ /* •*'- '•> Ox 'i V ,V;,>rt-, 1 ; , tJl- .»: *' J- ..j|< rnttrtp^V' ^■ O ■' M 0 A .j » . A. » X , . ^ -r - \ '■^ , -•( - ' t jt' • ' 4 ’ . 1 r • '• / - *,*,*< ’ «- V. .1 V u, ^ ^ , Iw -*«r -•.• , < . • . ' . V .1 .. \ ^ .'■■ -'V.i ; -V i II » «.» ’ *■ 1 . , 5 , , ,\ r> • ‘f. ir • -• .. .' . /tlii. oi ■ v. ■■ . f 'I '■. !' ']'''/• . ‘ ’ , t .. VO, * ' . i ■ • ''■•./■, • ■ ■ - '1 ■■ ■ :'y>. 'i, :..X ■ '' u' /•*•' .•: r ^ ... ' X ' r ... .. ,....■,; 'i:C . s i' oa L-i‘p‘i . A r. ■ X :-■- f-' ■ VJ ^ rK - ••- ^ 1 — .i-^t -T' ' ■ ■ '• .■ .'k.V.A' A‘;\'- «*-Vj -rff!.'- ■■ : IV ■ — V* I U V.-:. A*siWt.'‘' . T : fl -57- wide differences in the results obtained by the various investi- gators. Mention may be made of the fact that Reinke based his conclusions upon the results obtained from one or two plants. The uncertainties in drawing conclusions from few individuals have already been pointed out^ and it is probable that some of the discrepancies may be accounted for through differences in the number of cultures employed. In some cases, the differences obtained between plants growing in light and plants growing in darkness were ascribed to the presence of light or to the ab- sence of light, while other factors w^re disregarded. Under such circumstances lack of consistency in the results obtained may be expected. However, the evidence brought forth in this paper that light has a retarding effect upon growth should stimulate further investigation in this field. The observations in this investigation on the character of the root systems found on seedlings growing in soils of differ ent moisture content do not agree with those of Gain ('S5). This author states, "L'humidite du sol parait ralenter la croissance terminals de la racine principals, et exagerer la croissance dee ramifications secondaires et tertiaires. Ces resultats sent inverses de ceux qui on observe sur la tige.” Gain based this statement upon observations made on plants of buckwheat. Observations on seedlings grown in this laboratory indicate that, under a given set of conditions, plants differ in respect to the type of root system produced. This may account for the ■•"■* .,*«• J - 58 - differences obtained. It is probable also that differences in the nature of the soil will prove an important factor for consideration in accotlnting for this discrepancy. Aside from their importance to the botanist^the re- sults obtained in this investigation give promise of much worth to the agriculturist. Definite values from the agriculturist’s viewpoint cannot be assigned to them, however, until further researches are made. In assigning to them a value it must not be overlooked that this investigation was confined to a study of plants of the common bean in the seedling stage. Giving this due consideration, the results already obtained are suggestive and give some indication of what may be expected from plants in the more advanced stages of growth. If plants of other species, growing under natural conditions, prove to respond to moisture in a manner similar to that of seedlings of the common bean, the results obtained in this investigation will have wide application. If these results apply universally^, relative humidity and the evaporat- ing pov/er of the air may, in a large measure, be disregarded. The moisture of tjie soil, on the other hand, must receive greater attention. In the irrigated districts the relative humidity is lowland little may be done toward increasing it. The water of the soil, on the other hand, may be increased readily and any desired per cent of saturation obtained. In districts where irrigation is not practiced and where the supply of soil mois- ture depends largely upon the precipitation, greater attention -59- to the conservation of that moisture may he given. Briggs and Shantz (*13, *14) have shown that farm crops, producing an average yield, require from 6 to 18 acre inches of water for the completion of growth. Except in arid regions the annual precipitation greatly exceeds that required for the production of a crop. By employing the most improved methods of cultivation, the loss of moisture from the soil ^ay be re- duced to a minimum and the conditions for plant growth thereby improved. In the greenhouse, except in special cases, the relative humidity of the atmosphere may receive less attention^ while more attention is given to soil water. Through a more favorable supply of soil moisture the harmful effects high rates of evaporation and transpiration, brought about by low relative humidities and warm winds may, in a measure, be over- come. VIII. SUMMARY. 1. Elongation in etiolated shoots of seedlings of the common bean, growing in a pure silica sand either 20 per e cent or 60 per cent saturated with water, preceded rapidly in a relative humidity of 30 per cent as in a relative humidity of either 60 per cent or 90 per cent. 2. The shoots of etiolated bean seedlings growing in a pure silica sand 5 per cent saturated elongated less rapid- .r-,. : ■■ ■vi •,«! .i , " <■ j “• ' y . i'd vv-w-' V ' ^ ^ f * ■ t*‘ * * - ■ x , t ! ' ■»• V rjvvc/ijf' {- •: -. ,>-j * * ' -* VI < ^ ^ •'"i \ .. ui.« ' -r. I.. 'j&SXy , V ‘ '' ' ' ' ^ ^ ' ■ y . ' ^ ' h{‘ , *^ ' -U' r. , ;... ■ , •'. ' lid Vk. '■ C- . •!?* i.'l'iC a''’'-'i,‘ ^_ «-Ot S :;«V^ ... ; ...J! i o: • • j ^ f :• .•./.•^^.o.ii^3;» JBjjf f*' .brjVpi i :! 1 ■I ' • .'/■ " ' ■• ■', ; •’ 'om'. •V'^- ■ • i 't'l' t: 1 V*? -<■ M*.' J- _. - ‘ '•. - ^ -♦ V;. i'l-' , -"a M' v ••• .• •■: \’ ' J*'' it'* j ;W ■ '' 0 / • * %■ , 10' *: • . ■ i J ^ y I t II - - *i _i. ‘ * • , •*■ •'»*»• f • : L:J^> • ~ 4 % . j. . ^ t. f\ / '■'' ■ , ^ ^ i- , ■ ‘ ‘ . V , " ' ^ _L_^ fV .' ■', Ai' •>' t'.". >i 4 v .S > ‘U * '•■ ’ “ ^ .V .v ';,.;r;. ..‘•^, t „ c x._ / '••..y,?:.:^r4 - V ■ '^. •■ V- ■ ■ . ; '- ’'■-.t 'Pt Tx .^iVDo, i-‘^’ . ’:v> :q .■U- V V •• 4 Li' 4 , ■•'ill.. r'lf , V yirx‘ ■ ' . ^ . • ■ » •' •* •'^^ rjl • 'Yi '■'.I'x: ;f' ., ,,' U Ur> " " M}/ \ * - -■ -ii-snik : V. -60- ly in a relative hiujidity of 30 per cent than in relative humidities of 60 per cent and 90 per cent. 3. In a pure silica sand 5 per cent saturated, the shoots of etiolated bean seedlings elongated as rapidly in a relative humidity of 60 per cent as in a relative humidity of 90 per cent. 4. The rate of elongation in shoots of bean seedlings growing in darkness alternating with light appears to be in- fluenced by relative humidity in a manner not \inlike that in shoots of similar seedlings growing in continuous darkness. 5. The shoots of bean seedlings growing in darkness alternating with light elongate less rapidly than the shoots of similar seedlings growing in continuous darkness. 6. In the presence of both high and low relative humidities_, etiolated bean seedlings elongate more rapidly in a silica sand 20 per cent saturated with water than in a silica sand 5 per cent saturated with water. In a sand 60 per cent saturated^ the rate of elongation approaches that in a sand 20 per cent saturated. 7. The per cent of dry matter in the plant varies inversely as the soil moisture and the relative humidity. 8. Significant changes in the relation between the dry weights of roots and the dry weights of shoots were not brought about by increasing the soil water from 5 per cent saturation to 60 per cent saturation. I '■ ,<4. n f *^' rj ^ ‘^^'1 y 'y\v .j__ " VM :^1- >1. v^'. . - •® «... La . ^ ;'^&. 1 «■ . 'V 2 -if '. : • '*'•>.%'■■ ■■ ' . ■ -a. T'. :, .f-^fr>yy-:T.#1irafl - 'V ■ ■-.|r»«^ r ■ ■ - I . ki^f^ i vnjji J5^ ./ .,♦? i ?L«ai-'i' ,f ^-a<)lSSX<«^ V# S- ir^.’.- * '' V J Y *' 5'!^- V < fjlTa^ _fjpA* ^ ^ S"' ' u '■ ■ < ^-ji&sfc. ,•'■ iCvi ! ii'CS, -ix '^SSt^K^Tl -61- IX. CONCLUSIONS. 1. The influence of relative humidity upon growth in higher plants has been greatly overestimated. 2. In studies on growth in relation to relative humidity, the available moisture in the substratum must be recognized as an important environmental factor. 3. The harmful effects of low relative huijidity and atmospheres possessing high evaporating coefficients upon growth in plants, may be overcome, in a large measure, by main- taining an abundance of moisture in the substratum. ‘ j:/" w';'' 'v' - J>*'i''‘;/f^''‘*l^ "i m'Wv ■ "■' ' . - *'.• '‘.^v^*l’^" . ^ .''•i'. ,J" - ■ ■ ■ ' ^3 ■. ■ ■, ■ r " .-■'' : ,. ' V, ■ ■■%' .# Jm' &'* ,‘,* I,’ 7. ' j r?;.. 'ft, ■‘■ _ ,,,' w'V ' ■^ . , ■ ;■ .•■■■';, . ,, ' tiW’ JH.TJ > • r, ..' .V' 'y-f.jHi.jEA'*-'* ® '”l(r^nv.'«n; I ' : ,Ti ’ i’ J -§ 2 - X. Literature Cited. Abbe, Cleveland 1905. First Report on the Relation between Climates and Crops. U. S. Dept, of Agr. , Weather Bureau, BuU. 36. Anderson, A.P. 1894. The Grand Period of Growth in a Fruit of Cucurbita pepo Determined by Weight. Minn. Bot. Studies 1:238- 379. Askenasy, E. 1890. Ueber einige Beziehungen nwischen Wachsthum und Temper- atur. Ber. Deutsch. Bot. Ges. 8:61-94. Balls, W. L. 1908. Temperature and Growth. Ann. Bot. 22:557-591. Blackman, F. F. 1905. Optima and Limiting Factors. Ann. Bot. 19:281-295. Blanchard, H. F. 1910. Improvement of the Wheat Crop in California. U. S. Dept, of Agr., Bur. of Plant Industry BUll. 178. Bogue, E. E. 1905. Annual Rings and Tree Growth. U. S. Weather Bur. Monthly Weather Review 33:250-251. Bolley, H. L. 1901. Work with Wheat. North Dakota Ag. Exp. Sta. Rept. 11:28-31. Bovie, W. T. 1910. A Plant Case for the Control of Relative Humidity. Torreya 10:77-80. Brefeld, 0. 1877. Botanische Untersuchungen dber Schimmelpilze. Vol. 3. Leipzig. Brenchley, W. E. 1920. On the Relation between Growth and the Environmental Conditions of Temperature and Bright Sunshine. Ann. of Applied Biology 6:211-244. Brenner, W. 1900. Untersuchungen an einigen Fettpflanzen. Flora 87:387- 439. Baranetsky, J. 1879. Die Tftgliche Periodicitftt im Langenwachsthum der Stengel. Mem. de L’Acad. Imp. Sci. de St. Petersbouro; Ser. VTT g i-irr'f. Jbri^ ■'■'■ ■ • : c '•- TTv ■ '•' ■ \i ■'- ■ 1'- U ^ f K‘ , \ - '0SC4:-^i .-, IVJWX ! U • ^■■il >f- V' '. * , ^ /•' f f ' '* t. i. k’ i •.■: -*'J? i J,if,.ij” '.ol/rC' r.,- • -:f "t rN,',/.;'- .*:; .'v ’ f', i‘ . .■ ■ (, I 'i.-J. .V A : ■ •■ . . .Lx./'C • - . '■ ■ .*1 .V. , 1- • X. /TToii; i*. ;;. j ..- •* '• '•'»' ''■•»<.-• ’. )». . ■ ■* ‘ • ir.rtt ■ ;') V -»•' li'jr /T ■ r f ,/-A V'u: ■';■ /rX€. 9*^ ' /j:. .rfi'A: ; ;--».--mwr»ir,i<.^. -.T-V^VA -.— I" rr^v ^ 'f gj » ■' • -63- Briggs and* Shantz,H. L. 1913. The Water Requirements of Plants. I. Investigations in the Great Plains in 1910 and 1911. U. S. Dept, of Agriculture, Bur. PI. Ind. Bull. 284. 1914. Relative Water Requirement of Plants. U. S. Dept, of Agr. , Journal of Agricultural Res. 3;l-64. Bunger, H. 1906. Bber der Einfluss verscheiden hohen Wassergehalts des Bodens in den einzelnen Vegetationsstai»dien bei ver- scheidenem nahrstoff reichtum auf die Entwicklung der Haferpflanze. Landwirtschaft . Jahrb. 35:941-1051. Burkholder, W. H. 1919. The Dry Root- Rot of the Bean. Cornell Univ. Ag. Exp. Sta. Memoir 26. Clark, W. S. 1878. Observations upon the Phenomena of Plant Life. Ann. Rept. of the Sec. of Mass. Board of Ag. 22: 204- 312. • Clark, V. A. 1904. Seed Selection According to Specific Gravity. N. Y. Ag. Exp. Sta. (Geneva) Bull. 256. Cobb, N. A. 1903. Seed Wheat: An Investigation and Discussion of the Relative Values of Seed of Large Plump and Small Shrivelled grains. Ag. Gaz. N. S. W. 14:33-50, 145- 169, 193-205. Cummings, M. B. 1914. Large Seed a Factor in Plant Production. Univ. of Vermont Ag. Exp. Sta. Bull. 177. Darwin, F. 1893. On the Growth of the Fruit of a Cucurbita. Ann. of Bot. 7:459-489. Davenport, C. B. 1914. Statistical Methods. John Wiley & Sons. Davis, A. R. 1921. The Variability of Plants Grown in Water Cultures. Soil Science 11:1-32. DeCandolle^ A- 1905. (Cited by Abbe, 1905). - 64- Deep rez, 1895. Douglas, G 1906. 1909. 1914. Eberhardt, 1903 - Fittbogen, 1873. Free, E. E 1911. Fruwirth, 1917. Gain, E. 1892. 1895. 1895. 1896 - Godlewaki, 1891. • Selection of Seed Wheat. Jour. Agr. Prat. 59:694- 698. Abet, in Exp. Sta. Record 7:679. . E. The Rate of Growth of Panaeolua retirrugis. Torreya 6:157-165. Weather Cycles in the Growth of Big Trees. Monthly Weather Review 37:225-237. A Method of Estimating Rainfall by the Growth of Trees. Bull. Amer. Geog. Soc. 46:331-325. Ph. 1904. Influence De L’Air Sec et De L'Air Huraide sur La Forme et Sur La Structure Des Veg^taux. Ann. Des Sci. Natur. Bot. Ser. 8, 18:61-152. J. Unterauchungen ilber das f^lr eine i>ormale Production der Haferpflanze nothwendige minimum von Boden- feuchtigkeit, sowie tlber die Aufnahme von Bestand- theilen des Bodens bei Verschiedenen Wassergehalt desselben. Landwirtschaf t. Jahrb. 2:353-371. Studies in Soil Physics: V. Soil Temperature. Plant World 14:186-190. C. Schweres und leichtes Saatgut bei Luzerne und Esparsette. Fuhling’s Landwirtschaf t. Zeit. 66:396- 404. Influence de I’humidite sur la Vegetation. Compt. Rend. 115:890-892. Action de L'Eau Du Sol Sur La Vegetation. Rev. Gen^rale De Bot. 7:71-84. Recherohes sur Le Rble Physiologique de L'Eau Dans La Vegetation. Ann. Des Sci. Natur. Bot. Ser. 7. 20:61-215. 1897. The Physiological Rble of Water in Plants. Exp. Sta. Rec. 8:3-31. E. Ueber die Beein flussmng des Waohsthums der Pflanzen durch &ussere Faktoren. Bull. International De L' Ac. Des Sci. De CracoHie. Compt. Rend, des Sci. De L'Annee 1890:166-176. ... -V;. ^T v"^»” ■ ' 1* ■ ‘•V j ' i ' • » (,' , .•'0 ' 7^! .-laSi itot . t '- , f 2 Pi^i \ -. -i t L.i •^‘ r . ■.furl »'")■ r 70 t ^' I '’. «■ 7. .a^' \ ill >•. - • , XA '’.' * -• • '’. ■ - 1 ■ . *■ *» ■ iC rM ■ r 1 ?.'. i i ycv * w’.af ' . t- t.’ i \ * . ' v / vf ‘ : k;<. :r.i3( 1/ '•?! % ^ ' f '■ ■•*►• r . ■ ' .rd . , rtHv :-..' .. i c •V .3# r > ' V < V l > -J VC 'V ■,*'. _ Ji' ■ • * 11 # •u ■ ... ■ ■ {,• < v -' vtNi * ■ .. 4 ^,. ..:■ . . . r ic' *X \ - .. , , .’ ’'' . -, ’■ ■,i : Ui V . '7 a ;.* ■ ■’ . '’;-5 X : * -X- ! '■ *;"''r Ifi ' ' X • , , ' :. -■ : A ' ' . '. '* 'U •«.' i vi ».- v*.w 4 i-i V - ■>' ' ••'•• f / i #'*'', ' y !■ . o ', ■ i ■ ' . ■ ■ ’S. ■'■ . r ' i AV '/ I ' ,;■ ' ' ' % ■' . A ■- ■ ^ T*' f. : . • ^ / ♦. ^ » ». ' » ? » I • „ \ ; I ■ . 4 ' ft :, -i ' < 4 ., . f *: -„■'- •, ,i. , ,->'j i ' A ' r :, i r / . :. > A ■'4 ..- ■ i.' •I ,' ■' ' : ::.rI .'>4 - r .-'•lA',! ,;y '■•* -65- Godlewski, E. 1893. Studien fiber das Wachathum der Pflanzen. Abhandl. der Krak. Akad. Wise. Math. Nat. Classe . 23:1- 157. Rev. in Bot. Cent. 55:34-40. 1893. Greeley, A. W. 1930. Night Growth of Roses. Amer. Rose Ann. 1930. pp.40- 42. Grenfall, C. N. 1901. Some Experiments with Wheat. Ag. Gaz. of N. S. W. 12:1053. Haberlandt, F. 1866. Ueber der Einfluss des Saraena auf der Emte-ertrag. Bfihraische Cent, ffir die gesa^e Landeskultur. 4. Rev. in Jahresbericht Agr. Chemie 1866. pp. 298-300. Harris, F. S. 1914. Effects of Variations in Moisture Content on Certain Properties of a Soil and on the Growth of Wheat. Cornell Univ. Ag. Exp. Sta. Bull. 352. Hellriegel, Grundlage Des fflckerbaus • Braunschweig. 1869. Die Pflanzencultur im Wasser und Jhre Bedeutung ffir die Landwirtschfift . Die Landwirt. Versuchs - Stationen 11:111-112. Hicks, G. H. & Dabney, J. C. 1096. The Superior Value of large, heavy Seeds. U. S. Dept, of Agr. Yrbk. 1896. pp. 305-332. Hilgard, E. W. 1919. Soils, Their Formation, Properties and Composition. MacMillan Co. , New York. Hottes, C. F. 1921, A Constant Humidity Case. Phytopath. 11:51. Illinois State Water Survey 1915. Analysis of the Mineral Content of Tap Water of the Univ. of 111. Lab. No. 30486. Jost, L. 1907. Lectures on Plant Physiology. Authorized English Translation by R. J. H. Gibson. Oxford Press. , .rr:-. i.oiu^. r;'v*vr^ ,:Xw-.-,':ir 4 fckwiWwJl.^' ': " "yx ,■ ' ' •<' fWTA"*' ■•'0^.^v'''l'^W •••.;:*';XV »!■■•■ V»# ' • ( s ’11^ IV. V I -V> Ai-'B _ .. . ,- ■■•..I i j .. ► i'-tf. •■•ji ; J'x . ,. '.A . j\ .’I m I ^ : '♦. ■w \ ■ ■ 4 ^- ■ ■ . v' !irt :. . ., ■) . . ' '' •» •£•" f ‘ J j ■| ," .'^ :" •-' , ■;,; . . ..rjESr.f-.',, , 0 rr:^, diXut -ai .v ?.■ , '. 'i-.J 1 V ;i • 4 -• . . 4-'v C.. JT' ... . t.- t > . ^ f : V •‘ V ). • 't‘ t iTA -... '• " : f f -f. 1 iJL :^(3' • *4 5T4* «./ » :. . ■..•a.. •. ..' ,^-j ' ‘ ■■4 .., ' .7!,*, .#r . ' "i;;ur ., V , .V;: ■: c ■■.„■.■ > S -.' > ' A . ,-.. \ ti < ' ., U' il V M '*j,'V.. , .1a';, A'' . . J 1 'f f ' , . 1'- oi. ,OV'ite»..v. ’■ r-V* ' I V iQ;'l 'r ^ ’■ ' f f > ‘ ^ 'i, i - i > >' ■iV T?» . 4 h'. , ? j T • . U li ’ V ‘ i ' • /;;>• .L ■ ’ i .J ;■'.<■' - a; 7 ^'• ' ■ ' I , > ; :. U A .'fr ;5 ■ , 'i, . .i'J*"* v .(ri ' i 7 . ■• V'.;' • iarx't*. • '■■' U' •'V;' ::X. m 2 ' . /- «’ I «: - 66 - Kiesselbach, T. A. 1915. Transpiration as a Factor in Crop Production. Univ. of Nebr. Ag. Exp. Sta. Res. Bull. 6. Kiesselbach, T. A. & Helm, C. A. 1917. Relation of Size of Seed and Sprout Value to the Yield of Small Grain Crops. Univ. of Nebr. Ag. Exp. Sta. Res. Bull. 11. Kelsick, R. E. 1918. Some Observations on the Relation of Lint Length to Rainfall. West Indian Bull. 17:79-83. Kidd, F. & West, C. W. 1918 - 1919. Physiological Pre-Determination: Review of Literature. Ann. of App. Biol. 5:113-142, 157-170, 330-251. Kirkwood, J. E. The Influence of Preceding Seasons on the Growth of Yellow 1914. Pine. Torreya 14:115-125. Kbppen, W. 1875. Ueber die Wirkung der Temperaturschwankungen auf das Wachsthum. Arb. der St. Petersburg. Gesell. der Naturforschen 6:54-63. Kohl, F. G. 1886. Die Transpiration der Pflanzen. Braunschweig. Kraus, G. 1895. Physiologisches aus den Tropen. Ann. du Jardin Bot. de Buitenzorg 12:196-216. Lakon, G. B. 1907. Die Bedingungen der Fruchtkftrperbildung bei Coprinus. Ann. Mycologici 5:155-176. Lehenbauer, P. 1914. Growth of Maize Seedlings in Relation to Temperature. Physiol. Res. 1:247-288. Livingston, B. E. 1917. A Quarter Century of Growth in Plant Physiology. Plant World 20:1-15. 1918. Porous Clay Cones for the Auto-irrigation of Potted Plants. Plant World 21:202-208. Lock, R. H. 1904. On the Growth of Giant Bamboos, with Special Reference to the Relation between Conditions of Moisture and the Growth. Ann. Roy. Bot. Gard. Peradeniya 3:211- J V:;. 7 V'.™ .. ■ v ',3 >1 ^ ■, vii .nt-i" 1 ':;,t '. .JL ;.\ . iCjtJV .- 1/ .. rJ ..'>■ A"' V ■•• . . .. >• -'• 'to .. . >■ v'"' ■' ^ '- 1 ^"' . . V" ■■ V' ■OJ 'V‘^.' I'liCtiriTJ r«nc '*■ c - » ■; .'• T'f 1^*4 '•* 4 .'.. ' A./li-fc. . i T ;r ^ *lo r* i\' ', - r» A 'i t« iT ;. Stills r ' Vl ‘■'ilr' ‘ft'. • . .#» H .V .^<1 * '. ■ ■ •• ■ ■ t' :■' • 'i'- rtiii* Jj. : •>'' I m '■• .."r■^':^e:I*,^■!■;y^f^:r^.oT ,reL iU ' . '-'?t/ri;, A '..,■* , 0 ,'j r.o ,.;#■ "a- , f . , .■ J... ■ n%}] 'Ji X flf,, */• • ..'j . .. ;*c., . :iii> tf'i'J: '•. lfi:;S. ft . > " ■ f 'K : ^ ■■ ',• •> ^r: Vv'..» ‘ - ■ *4- <* ■:.?! 'iffl >vffC ' ....•- - r**/ V rv’: "■ .1 ,':vi ; / i‘'.i/4 r.i «s^fVvVU? . ' -■ '.Ti’jr . m, ,» V- '■ ■.■ f-: . ■ i i-.rtfcH V"' ■•(.■. r ■ U' i-: :.6uAi!T.'Xl ... .-. •• V ;?•■• 0, ,ird3 .i ■ni'- 'v‘..; . 'Ivr'X . ~’i , k- « f. I, I— - -VrY-ayi-^rjr* f . ' . •.>.,'-V ■ '. ' . ' ^x•, i_ ^ :. ,v. . ^ ■ t ■•-. jts 'T".^‘'•^ j: 'V:? ; '-'tj<*' ■ r' J -67- Love, H. H. 1912, A Study of the Large and Small Grain Question. Ann. Rept. of Amer. Breeder's Assoc. 7^8:109-118. Lyon, T. L. 1905. Improving the Quality of ViHieat. U. S. Dept, of Ag. Bur. PI. Ind. Bull. 78:30-35. MacDougal, D. T. 1903. Soil Temperature and Vegetation. Monthly Weather Rev. 31:375-379. Maxwell, Walter 1896. The Rate and Mode of Growth of Banana Leaves. Bot. Cent. 67:1-5. Mayer, Adolf 1898. trber der Einfluss Uleinerer Oder grflsserer Mengen von Wasser auf die Entwiokelung einiger Kulturpflanzen. Jour, fdr Landwirtsohaft 46:167-184. Meyer, E. 1829, Ueber das periodisohe tSgliohe Wachsthum einiger Get reidearten. Linnaea 4:98-113. Middleton, T. H. 1900. The Effect of Size of Seed on Crop. Univ. Coll, of Wales Rept. 1899. pp. 68-70. Miller, F. G. & Pamrael, L. H. 1901. A Study on the Germination and Growth of Legurainosae , especially with Reference to Small and Large Seed.. Iowa Ag, Exp. Sta. Bull. 62. Montgomery, E. G. 1908. The Use of the Fanning Mill for Selecting Seed Wheat and Seed Oats. Univ. of Nebr. Ag. Exp. Sta. Bull. 104. 1912. Competition in Cereals. Univ. of Nebr. Ag. Exp. Sta. Bull. 127. Pagnoul , A, g 1900. Ueber den Einfluss der No. derschlS^e und der Boden- beschaffenheit auf die ErtrSLge der Futterpflanzen. Biedermann's Cent, f^r Agrikulturchemie 29:16-19. Pearson, G. A. 1918. The Relation between Spring Precipitation and Height Growth of Western Yellow Pine Spplings in Arizona. Jour. Forestry 16:677-689. i - 68 - Polle, R. 1910. Uber den Einfluss verschieden hohen Wassergehalts, verschledener Dungung und Festigkeit des Bodens a.uf die Wurzelentwicklung des Weizens und der Gerste im ersten Vegetationsstadium. Jour, fflr Landwirtschaf t 58:397-344. Prantl, K. 1873. Ueber den Einfluss des Liohts auf das Wachsthum der Blatter. Arb. Bot. Inst. 1:371-384. Wurzburg. Preul, F. Untersuobungen fiber den Einfluss verscheiden hoben 1908. Wasaergehaltes des Bodens im deit einzelnen Vegeta- tionstadien bei verscbiedenen Bodenreichtum auf die Entwickelung der Somme rweizenpf lance. Jour, fflr Landwirtschaf t. 56:339-271. Prianishnikov, D. 1900. The Influence of the Moisture of the Soil bn the Growth of Plants. Zhur Opuiton Agron. 1, No. 1, 3-t20. Abst. in Exp. St a. Rec. 13:631. 1901-1902. Reinitzer, F. 1881. tJber die Physiologische Bedeutung der Transpiration der Pflanzen. Siztzungsber. K. Akad. der Wiss. Math. Nat. Classe, Wien 83:11-36. Reinke, J. 1876. Untersuchungen fiber ?/achsthum. Bot. Zeitung 34:91- 95, 129-143, 145-159. Sachs, J. 1860. Physiologische Untersuchungen fiber die Abhangigkeit der Keimung von der Temperatur. Jahrb. fflr Wiss. Bot. 2:338-377. 1874. Ueber den Einfluss der Luft temperatur und des Tages- lichts auf die stundlichen und taglichen Aenderungen des Lingenwachsthums (Streckung) der Intemodien. Arb. Bot. Inst. Wurzburg, 1:99-192. 1892. Ueber die obere Temperatur-©renze der Vegetation. Abhandiungen fiber Pflanzen-Phvsiologie 1:111-136. (From Flora, Regensburg, 1864; Sanborn, J. W. 1892. Selection of Seed. Utah Ag. Coll. Exp. Sta. Rept. 3:133-137. -.’jrsjMliW-.' -vi'i" •-' ■ r ,: -i : »(?->» r-Tfn»^ ’.T,\T ■ ,, "* V , ■if •*i f- ■I •.! ■ •U .c:!al.'. 8 ^ ,j % ,?v. ^ -V Qv . ■' ■' /'■ ‘j‘> / . . b;r’; -’iV '0t. ‘’"' , . " ' x" •■i ;jr.08« ». ..-riil-'b ;• :.v i. V ^ ^ f ' . ' r ’ ' ^ V . ’•...' wi ■i ■ Xii&t . * u b'' ■;'. ..'ft'-" r:^ .: • ■Alfc* ' ' 1 ,■ O • ». v» ' ! ^ '. 5/^V; >’*'' f }■ i^ , -t'* .•'c.-iTc-: : .vCi, i; *, T - e;ii *'rj ' ' r i.. eft* n '- ::. ct/itak' ■. ■ . ■/'ariy A*. ^ *;ev : '/v-, . ^ L:e^i ' : ^ae..iiem.9 ...>r-*v ic-r*. a -;c-> ■/»•-«?•. fi f 4 1 .’ ■■ . ‘ - v.-?- .1 I . ; 1 . . ,cvJ. ■ ‘•-i yO ‘;r ' . .. :i . - i': . ,. JO*' . "■’ vv’. i*-rs •W. ': - u s r. •, . J I i ^ < •i,e4S -■' .resf .viW :,r-! . ■; KaI-. ■ i ’ . .. «(,>^ V; '«. f''ip.ij? livi ., ..i». ••*.1 . /■ i ,f : .yjv t :.' ; . i;.' t ;•.". L '-j •• - • ’. f . 1 - V r.c-y _ • ;y0 ' . a ' . ' ' * . r * '■■' ' ^3 jrt"- ■.• ^&3c..:.ry. ;- •;.;:if ‘ . ^>1,. *r;*^ . <■ ■'^ e;;:*i:,v3p‘V-, ' Tik,-ie^ i ■: ;^d&‘ z^.^f ' ''. ' ’■ ,' /' ' ■ I, .» »’ V f 1 . . .V - tAi/ ' i ,7 l\ • !■ < ■ • >• ‘.*1 ' * . ^ ., , V' *■ -*s K - ^ ;■' x \ • ••■ .vt.,i .■. .nni/ ■■■> /'. ,>v; 7 j' - 69 - Sohaible, 1901. Sohroeder 1896. Seelhorst 1900. Seelhorst 1903. Seelhorst 1910. Shamel, A 1905. Shaw, G. 1906. Shibata, 1900. Shive, J. 1920. Smith, A. 1906. F. Physiologische Experiments dber das Wachstum und die Keimung einiger Pflanzen unter Vermindsrten Luft- druck. Beitrage zur Wiss. Bot. 4:93-148. R. R. Development and Transpiration of Barley under the Influence of Different Degrees of Humidity and Nutri- tion in Culture Media. Ann. Inst. Agron. Moscow 2, No. 2, pp. 188-226. Rev. in Exp. Sta. Rec. 8:954- 955. 1896-1897. C. Neuer Beitrag sur Frage des Einflusses des Wasser- gehaltes des Boden auf die Entwickelung der Pflanzen. Jour, fdr Landwirtschaf t 48:165-177. C. and Freckmann, W. Der Einflluss des Waasergehaltes des Bodens auf die Ernten und die Ausbildung verschiedener Getreide- VarietSlten. Jour, fdr Landwirtschaf t 51 *.253-269. C. and Kizymowski Die Bewurzelung verschaidenen Sommerweizen Variet&ten. Jour, fdr Landwirtschaft 57 :115 t' D. The Improvement of Tobacco by Breeding and Selection. D. S. Dept, of Ag. Yrbk. 1904. pp. 440-442. • The Selection of Seed Wheat. Univ. CalSf. Ag. Exp. Sta. Bull. 101. Beitrage zur Wachstiimsgeschichte der Bambusgewdchse . Jour. Coll. Sci. Tokyo 13:427-496. W. Relation of Moisture in Solid Substrata to Physiologi- cal Salt Balance for Plants. Jour. Ag. Res. 18:357- 378. M. On the Application of the Theory of Limiting Factors to Measurements and Observation of Growth in Ceylon. Ann. Roy. Bot. Card. Peradeniya 3:303-375. • n> ; ' ■* • • \ M -:PS ‘. i.OV V '... r-rJ ..- 'V •: •‘ jj'.v :' i. ....’ii "V ,^ p :.: f . ^ :*.■ , i -c , i ] ■•' , , „’ f -' ,.Qr^^ .^Ov' . ^^u; t-:; ^ J . v8 , ,,. " : ' ■ ] V j • .,,'T 1' .j,.;:u'v8:J7:v’'v ' ^ " * ■ i. ■'.X^li "■ --( . r. - -'vVa ' ij: ' .■ ‘i- ■ - V . ' ' f ■ ^ ,•-'■* \; i m' ■ ; il ,' *L-'i'^si4 •-■- . •Ji , . .;' 3 'I .. V '\ J t »!, .; .. ;., • ;C . , ., ■ ■■ . I’C, lifflV’ itrt' . ' I" '-:rr.- ‘ :. *■' bltUK'i^'T-^'^* -? a i -i (- - ' ' n 4 / 4 J I V . ti . .; . t'i— -i' . . i ./ „ -vJbt::' ■•■' to ;v.---.':v>' .cr" . s ' ‘ • % r , ft ’. , , r. • j i % xH ■:*. • ^f , j .0^'r-Vc#: J . t' r; . 4' « . 5 j ' , . ' ^ .'^’. '. ‘ , ■ ' .1 . t . ' , I ' ' ■' "'.i " >■ * V ' »•»' ' • ,• •- ■'■V ^.o«r ■■ '.xr. . .', ''■' t A''. ■ ■% ■ ' "'. .' ' ' . ■'•1 ftf ' i . ■ 't .V ., ^' • •• ■ ■ ' ■t -Tr- ":; ir rJtifjs.V:- „ .^JfOTfV; '■ ,_„ .-. ■.:,.; i : nS ! . 00 ^.. V r r * ^ ^ ^ ■ ^ , v ' ■ ' , * 1 Y,U ..•'“. ir :* rr-=^«^-.r V'i “Ilf ^ »70» Snyder, H. 1905. Heavy and Light Weight Grain. Univ. Minn. Ag. Exp. Sta. Bull. 90. Sorauer, P, 1873. Einfluss der Wasserzufuhr auf die Ausbildung der Gerstenpflanze. Bot. Zeitung 31:145-159. 1878. Der Einfluss der Luftfeuchtigkeit . Bot. Zeitung 36:1- 13, 17-35. 1880. Studien fiber Verdunstung. Forschungen auf den Gebiete der Agrikultur Physik 3:351-490. Soml, A. M. and Vanatter, P. 0. 1901. Winter Wheat. Univ. Tenn. Ag. Exp. Sta. Bull. 14, No. 2. 1901. Winter Cereals and Legumes. Univ. Tenn. Ag. Exp. Sta. Bull. 14, No. 3. 1903. Influence of Climate and Soil on the Composition and Milling Qualities of Wheat Univ. Tenn. Ag. Exp. Sta. Bull. 16, No. 4. Stebler, F. G. 1878. Untersuchungen fiber das Blattwachsthum. Jahrb. fflr Wiss. Bot. 11:47-123. Taylor, E. P. and Downing, G. J. 1917. Experiments on the Irrigation of Apple Orchards. ■- Univ. of Idaho Ag. Exp. Sta. Bull. 99. True, R. H. 1895. On the Influence of Sudden Changes of Turgor and of Temperature on Growth. Ann. Bot. 9:365-402. Tschaplavitz, F. C. 1886. Untersuchungen fiber die Wirkung der KLimatischen Factoren auf das Wachsthum der Kulturpflanzen. Forschungen auf dem Gebiete der Agrikultur Physik 9:117-145. Tucker, M. and Seelhorst, C. 1898. Der Einfluss welchen der Wassergehalt und der Reichtum des Bodens auf die Ausbildung der Wurzeln und der oberirdischen Organs der Haferpflanze aus- flben. Jour, fflr Landwirtschaf t 46:52-63. ^ ,.T^ 'iii-v'V* ‘ 'i: > * /-...' -■I ':f " \ :j tt:^* f .• > ■ 1 ..i i * , -'t W I * %4 .-. • •*• jt- - ^IL y . I, X < <• •■ •• ; r> s’ It ■ I .1* ,c<.> : ■•■ .1 , , ( .^i:. ■I’l ^ . 1 . ---f* :•;: .4 ''.’.Xiti' • ' ■’ 'JO, , • . r‘r . •V .’‘v ■ 'V.-. . . * . . ^ • -U vi '%f;9 V , ' . ■' ,'‘f»i ■ ’ , 1 '• . .♦B oK:’ 's. V, • - > 1 ' J 'i^ , ■ • • -n- > . ■' ■§■ /v •' / ■ ■■ '^vyk:^ te- ■ ' ‘j*k- >■■ I ^ '*• , \ ) 1-4.- ■4 V ■■JCa ,ii^ ;•;<-.••■ • , > )G'fi .X X. / ,>:V^, I ^ r ■■* , '■ W - -'A , ^ . i S - i'-' ^■ • , ■" *. A ;\' '• . '■ ■ ' - i/i . ^ il’ - I'. y -f K.-'.' " •_ .u t S'" X ,' 45 :•,©? I v‘> * . ■• ;./vi... r/A, ' " i' i(i; -J i ' ■ • ^^i;/•'l;^:i• *! ■; Afi •■ ’f^b : "■ '•4, '. *v t ; ■ >»' : J>:'{ t . ' .. .^.■' .14 4." ,'rM * I -71- Vesque, J. et Viet, Ch. 1881. De L' Influence du Milieu sur Des Vigitaux. Ann. Des Sci. la Structure anatomique Natur. 12:167-176. Vogt, Ernst.. 1915. !Jber den Einfluss des Lichts auf das Wachstum der Koleoptile von Avena sativa. 2eitschrift fftr Bot. 7:193-270. Walls, E, P. 1905. The Influence of the Size of the Grain and the Germ of Com upon the Plant. Univ. of Maryland Ag. Exp. Sta. Bull. 106. Ward, H. M. 1895. On the Biology of Bacillus ramosus (Fraenkel) a Schizomycete of the River Thames. Proo. Roy. Soc. London 58:265-468. Webber, H. J. and Boykin, E. B. 1907. The Advantage of Planting Heavy Cotton Seed. U. S. Dept, of Ag. Farmers' Bull. 285. Williams, C. G. 1903. Experiments with Oats. Ohio Bull. 138. 1905. Experiments with Winter Wheat. Ohio Bull. 165. Wollny, E. _\1877. Untersuchungen dber die Werthbestimmung der Samen als Saat - und Handelswaare. Jour, ftlr Larrwirts- chaft 25:75-116, 133-169. 1886. Untersuchungen dber den Einfluss des Specifischen Gewichts des Saatgutes auf das Product ionvermSgen der Kulturpflanzen. Forschungen a. d. Gebiete Agrikultur-Physik 9:207-216. 1888. Untersuchungen dber das Verhalten den Atmospharis- chen Niederschl&ge zur Pflanze und zum Boden. Forschungen a. d. Gebiete Agrikultur-Physik 10:153- 178. 1892. Untersuchungen dber den Einfluss des Wassers auf das Wachsthum der Kulturpflanzen bei versciedenen physikalischer Beschaffenheit des Bodens. Forschungen a. d. Gebiete der Agrikultur-Physik 15: 427-432. isvir' ■ 5 -r, -^ -,;.7-.,>,- n- ir?.- » , > j* '■ t' 8 «f . . • *V, ^ * ' ii/*> V > % t - - ;x- :♦ A-"Su' ■ ,•;. . k '-' .1 r»* C • ^ ^ ’•f *»* Wt ( • ^ % V ^ ^ - *' •' -'i c-M r . i.';; 9 V'1 ■Sfl . t|5ar . •'• fr :-s' 0: . ; ik. rtii ^-0" » . 4 . . J Wi A' ■ J • . I ^ 1 / - ! ,f- .... *A. ‘ I * . I r ^ ' §»' !•'.. ,.. r'S/.VOg » ■ , t .t “■ ,• , .r'’- » » ■ ;■ c;*-fr . : ,r’ .”\t«cv •■•;-.fi-ri-.' .-. , -it'i . * :>;; ^ I f: * • . ',r:. . .ms.-':- .. . k .U . >> . ■: • .• , - f.V . ; . ... 7 ,V'' ' ■ <-.p fif. . . iV'*' _ ; .T^, . ■'71.7 .>',j f . :, ' .'i‘T • -• • V .V ' ■ ] «i* T r, V .■ , ' ' f . ■ s? , ^ 7. ./» • '> 't^C! 1 ’ ; ‘ -1' ij .? '. .47'V 'V i .'.r ^v :. : .iXidcpiit^ ‘ ' \ih . / I' . .u - ki V*? ’ ' . ’ X- f« :-;.N '■‘Jr •-'■ ■-•S^SA-u;; ■•■ ■•• tr,.-iv-''. y-.rr ...' *' mt >., ' \tilk .'''■•?, ti/: .-■.'v 4 - ‘ >.1 / -I • ' :1 -72- Wollny, E 1897. Wollny, W 1098. Wood, T. 1911. Untersuchungen Clber den Einflus* der Wachsthumsfak- toren auf das Produktions vermdgen der Kultui^pflan- zen. Forschungen a. d. Gebiete der Agrikultur-Physik 30:53-109. Untersuchungen dber den Einflusg der Luftfeuohtig- keit auf das Wachsthum der Pflanzen. Forschungen a. d. Gebiete der Agrikultur-Physik 20:397-437. The Interpretation of Experimental Results. Jour. Bd. Ag., Great Britain, 18, Supplement 7:15-37. - 73 ~ XI. VITA. The author of this thesis was born at Watford, Ontario on December 1, 1892. His early education was received in the secondary schools in his native village. He was graduated from the University of Toronto with the Degree of Bachelor of Scientific Agriculture in May, 1918. In January 1919, he entered the Graduate School of the University of Illiinois and obtained the Degree of Master of Science in March, 1920. He was registered in the Graduate School of this University during the Summer Session of 1919 and during part of the Summer Session of 1920. During his residence at Illinois he has devoted full time to study for an ad- vanced degree.