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THE DEPENDENCE OF GROWTH UPON TRANSPIRATION

UNDER DIFFERENT CONDITIONS OF HUMIDITY

MINOR THESZS

Presented to the

DEPARTMENT OF BOTANY

Foy the Desree of

MASTER OF SCIENCE IN AGRICULTURE

By
Charles Frederick Clark, B. 5S.
Cornell University

June, 1907

THE DEPENDENCE OF GROWTH UPON TRANSPIRATION

UNDER DIFFERENT CONDITIONS OF HUMIDITY.

The phenomenon of growth is one of great complexity
it being the resultant of several processes which are
carried on within the plant, the several factors concerned
with it being in turn influenced to a greater or less de-
gree by external conditions.

The relation of one of these processes, transpiration,
to growth has given rise to mich discussion among plant
physiologists and is still an unsettled question.

Among those who look wpon transpiration as primarily
a vital process there are three general views held regard-
ing its role : (1) To enable the plant to take up a suffic-
ient supoly of mineral salts ; (2) To prevent high temper-
atures in the plant ; (3) That it is a necessary evil,
necessary in that moist membranes must be exposed for the
exchange of gases and at the same time an evil since such
large quantities of water are required.

Strasburger, Woll, Sehenk and Sehimper (12) hold that
-<the plants would be unable to obtain a sufficient supply of
nutrient salts if they took up only as much water as they

could retain and make use of.

They also consider transpiration necessary to secure a
proper concentration of those salts.

Pfeffer (9) regards transpiration essential for the
distribution of mineral salts in the plant and even main-
tains that srovth varies with the transpiration. Iie alse
thinks it probable that transpiration influences the ex-
change of gases. If it were not for transpitation, the
intercellular spaces would become filled with rater which
would prevent aeration of the tissues thus retarding meta-
bolism and growth. On the other hand, in the presence of
a limited supply of vater in the plant, the diminution of
transpiration must of necessity interfere with the free ex-
change of gases thus inhibiting the assimilation of ce.

Sachs (10) in commenting woon the fact that assimila-—
tion may be carried on in land plants which are surrounded
by a saturated atmosphere, points out that the assimilation
in this case is extremely feeble and furthermore that even
under these conditions transpiration may occur to a slight
degree and a feeble flow of water maintained.

Edmond Gain (2) concludes from the works of Hellriegel

Haberlandt, Wollny and others that a certain relation

exists between the amount of dry matter elaborated and
the weight of water transpired by the plants during vegeta-
tion. This view is also held by Lawes and Gilbert (7).

Green (4), in addition to the view that transpiration
is necessary in order that the leaves may be supplied with
inorganic salts, maintains that it is imperative in order
to prevent a rise of temperature to a point which would be
fatal to the plant. He states that the amount of radiant
energy taken up by the leaves has been computed to be near-
ly 50 times the amount which can be utilized in the process
of photosynthesis ; if the heat were allowed to ee
in the leaf unchecked it has been calculated that its tem-
perature would rise during bright sunshine more than 12°
C. per minute. Pfeffer (9) and Tschaplovitz (18) also
recognize the probability of a regulatory influence of
transpiration upon the temperature of the plant.

Kreusler (6, See VYoods, 15), does not regard the check-
ing of transpiration by a complete saturation of the at-
mosvhere as unfavorable to assimilation but, on the other
hand, holds that assimilation may be reduced by a dry at-
mosphere, which is conducive to excessive transpiration,

long before the turgescence of the leaf is visibly diminished.

Barnes (1) advances the theory that the amount of
Salts absorbed is dependent unon the living cortex of the
rootlets and the mesophyll of the leaves. We states, "it.
the cortex be freely permeable equilibrium in the distri-
bution of any given salt will occur, assuming for a time
no evaporation from the serial parts. If then evaporation
concentrates the solution the higher diffusion tension of
thet salt will tend to drive it to those regions where the
diffusion tension is lower. This tendency, therefore,
“would operate against the further supply of that material
in the leaves. If the cortical layers be not freely per
meable, the amount absorbed is regulated wholly by proto—
plasmic activity and cannot be affected directly by outside
supply. The phenomena of selective absorption show that
transpiration does not determine in those cases the amount
of salts absorbed."

The experiments conducted by certain investigators
serve to indicate that an increase or decrease in trans-
piration, as influenced by the humidity of the atmosphere,
does not necessarily produce a corresponding increase or

decrease in growth.

<7

Godlewski (8) found that a sudden in inerease or de-
crease in humidity produced a corresvonding change in
growth which, however, was only transitory. At the end
of one-half hour it returned to its former rate. This led
him to the conelusion that the action of humidity vas not
to change growth but to produce a change of turgescence and
consequently tursger—distension.

Sechlésing (11), working with tobacco plants, found
that transpiration was greatly decreased by a moist atmos-—
phere while the gain in dry substance was increased, the
plants in the moist atmosphere gaining 5.2 grams per liter
of water evaporated as against 1.2 grams in the dry atmos-
phere. The composition of dry matter was also found to
vary under the different conditions of humidity, the per
centage of ash being 18 in the moist atmosphere and 21.8
in the dry. In commenting upon this fact, Schlosing
states that all tobacco plants of any source, species or
degree of development, examined by him, have given in the
vicinity of 205 of ash, hence the plants grown under humid
conditions were abnormal in this respect.

Wolliny (14) found that the dry weight and total amount

find that the quantity of water transpired by some of our
common field crops during their period of growth is not a
measure of the amount of dry matter formed. That the

ratio between these quantities is not constant is shown by
the following table which gives the amount of water trans-

pired per unit of dry matter, as determined by different

investigators.
TABLE 1.
Lays and

Gilbert Hellriegel Wolliny King
Wheat B25 | 259 - ss
Barley 262 210 393 774
Oats - 402 557 665
Red Clover 249 ; 8380 4538 -
Peas 235 292 477 4447

In commenting on these results, Hall (5) says, "Phe
divergencies in these results are intelligible if we con-
sider that the transpiration process by which the vater
is lost and the assimilation process by which the plant
gets heavier have no necessary connection, the both become

active under the same stimuli of light and varmth."

The numerous modifications of desert plants for the
purpose of reducing transviration have been considered by
some as evidence that this process is not essential to the
grorth of plants. It must be borne in mind, however, that
under these conditions transpiration is still carried on
to some extent, furthermore, the conditions are so faveraple
for excessive transviration, that were it not for these
special adaptations the plants would soon be deprived of
their limited supply of vater.

The exneriments described on the following pages were
undertaken with a view toward determining what relation, if
any, exists between transpiration and srovth under aiffer—
ent conditions of humidity.

Five svecies of plants vere employed for this purpose,
viz., corn (State Flint), sunflowers, peas, wheat (Dawson's
Golden Chaff) and buckwheat.

The plants were grorn in wire baskets 3 inches in dia-
meter and © inehes deep. The manner of preparation was
as follows : The tops of the baskets were first dipped in
melted paraffin to the depth of about one inch. This

formed a collar around the top which prevented the paraffin

from flowing over the surface of the soil while the remain-
der of the basket vas being coated after filling. It also
prevented the water which was added from time to time
during the experiment from flowing off at the sides of the.
basket. The baskets vere filled within three-fourths of
an inch of the top with soil which had been thoroly mixed,
pulverized, and screened to remove the lumps and stones.
They were then dipped in paraffin until coated sufficient-
ly to prevent loss of water. The paraffin also served to
cement the soil particles on the outer portion of the soil
cokumn to the sides of the basket, thus preventing the
formation of an air sovace between the soil and basket.

The seeds were soaked in water before planting until
germination had commenced. This method of treatment hast-
ened germination and also enabled a selection to be made
of seeds which were of nearly uniform vigor, thus eclimina-
ting to some extent extremes of individual variation. A
few more seeds were planted than the mumber of plants re-
quired. This permitted another seleetion to be made after
the plants had begun to grow. When the plants were 2 to

21/2 inehes in height, they were thinned to the required

10

number and the tops of the baskets sealed to prevent evap-
oration from the surface of the soil. This vas done as
follows : A circular piece of paper having a diameter a
little less than that of the basket was dipped in paraffin
and a slit of sufficient length and width to admit the
young plants vas cut into it. Previous to sealing a layer
of fine sand, about one-fourth ineh in thickness, was
added to each of the baskets to aid in preventing evapora-
tion from the surface of the soil. The paper vas then
adjusted and fastened in place by running melted paraffin
around the edge, thus cementing it to the sides of the
basket.

The amount of paraffin added vas determined by veigh-
ing the baskets before and after sealing. The difference
added to the weight at planting gave the final ee
i.e., the weight of the paraffin and basket plus that of
the soil in which the moisture content had, by the addition
of water, been brot up to the amount considered to be most
favorable for the growth of plants.

The loss of vater by transpiration was determined by

weighing the baskets at intervals of three or four days.

iz

Water was added at this time until the weignt of the basket
was a few grams above the optimum, the excess depending
upon the rate of loss.

The plants were divided into three lots and each sub-
jected to one of the three conditions, which vere designa—-
ted as dry, check and moist. The three lots were Placed
abie side in the greenhouse, the dry and moist being
under bell-jars while the check was un#nclosed.

The average relative humidity of the dry was 78°, of
the check 88°and of the moist 98°. The excess of moisture
was removed from the atmosnhere of the dry, by placing
calcium chloride in onen dishes under bell-jars. The
calcium chloride was changed as soon as it had become sat-
urated with moisture, usually morning and night. The high
degree of humidity of the moist bell-jars was maintained
by placing pieces of wet filter paver under them.

The ee mere aerated each morning in the fol-
lowing manner : With those subjected to the dry conditions
this was accomplished by forcing air, from which the moist-
ure had been removed by passing thru a column of calcium
chloride and pumice stone, into the bell-jars. In the

ease of those in which the moist conditions obtained, the

12

air was changed by removing the bell-jars for a few minv-
tes. This was done at a time when the mmidity of the
atmosphere in the greenhouse was relatively high.

The temperature of the three conditions was the same
as that in the open greenhouse, viz., about 65°F. during
the day and 60°F, at night, ex2e>t that on bright, clear
days the rays of sunlight caused a rise in temperature of
several degrees in the bell-jars above that in the open
greenhouses This change of temperature vas the same in
both the dry and moist. The temperature factor must be
taken into consideration when comparing the eheck with the
other two conditions.

The folloving table gives the number of baskets used,
the mumber of plants in each and the date of the beginning

and end of the period during which transpiration records

were taken.

12

Table II.
Kind of No.of No.of Beginning of End of
Plant baskets plants in trans. period trans. period.
each.

Corn --- 12 --- 2 --- Feb. 2 --- Feb. 22
Sunflowers 9 --- 2 --- Feb. 2 -- Mare. 2
Peas --- 9 --= 2in6 Feb. 17 --- Mar. 7

8 in 3
Wheat ---9 --- 6 --- Mar. 5 --- Mar. 23
Buckwheat 15 -- 4 --- Mar. 19 Apr. 5.

At the close of each part of the exneriment, which

was on the date indicated in the last column of Table II,

the plants were cut ai the surface of the soil, measured,

the green weight, dry veight and ash determined, aiso the

ratio between the water transpired and the dry matter pro-

aducede

The results are given in the following table :

TAgLe Tits

14

Av. Green Dry % % Water
ht. weight matter dsm. Ash ash Trans. transp.
Ome gms. pris. gms. in ems. per am.
delle eM. gms.
Corn -

Dry 42.2 25.0 1.9630 7.35 .8405 17.35 380.0 193.6
Creck 39.2 25.4 LeBl77 7515 ».2227 17.75 180.9 99.5
Moist 389.9 27.0 1.8352 6.80 .2274 18.38 1238.9 67.5

Sunflower

Dry ._ 29.9 19.6560 1.6140 8.21 .3878 24.02 G15.0 381.66
Check 24.5 16.7638 1.23115 7.28 .2910 24.92 348.4 287.58
Moist 25.6 15.0080 .8565 5.71 .2295 26.80 110.2 128.66

Peas-

Dry 40.2 9.2865 .7992 8.65 .1178 14.74 3227.3 284.41
Check 87.0 9.0737 .%7406 8.16 .1071 14.46 154.9 209.10
Moist 42.9 9.7130x% .9145 9.422.1144 12.51 46.4 50.74

wheat -

Dry 382.2 6.1905 .8545 13.81 .1300 15.21 302.6 354.00
Check 23.4 4.3537 .6307 15.84 .0794 11.51 155.9 226.04
Moist 28.0 7.6445 -9665 12.64 .1335 13.81. 95.4 98.71

Buckwheat -

Dry 17.8 10.5875 .9720 ©.18 .1682 17.30 299.8 208.44
Check 14.1 6.8085 .6845 9.61 .1110 17.50 159.8 $51.07
Moist 23.6 10.6190 .9815 8.77 21625 17.44 122.4 131.40

ta

x. Figures too lor.

weight.
Ze Figures too high.
than figures for

The plants wilted very rapidly as soon
as removed from the moist atmosphere thus reducing the

Same reason as above.

"ary" s

Should be less

Le

An inspection of this table shows that height, tobal
weight and composition are influenced to a greater or less
degree by the amount of water transpired, the direction and
extent of this influence varying with the species.

It will be noted that in the first two series the re-
sults for the checks are, in general, intermediate between
those of the dry and moist, while in the ease of peas,
"heat and buckwheat the results are lower than those ob-
tained under either of the other two conditions. This is
attributed to the fact that the three last series, named
were run later in the season (see table II) when the number
of hours of sunshine per day was greater, as vas alse the
number of bright, clear days. The effect of this was to
eause a rise of temperature in the bell—-jars above that of
the air surrounding the check plants. Since we have an-
other factor entering into the problem which exerts a con-
Siderable influence on growth, the results obtained from
the cheeks are not comparable with those obtained under
the other conditions, hence they will be omitted from the
present discussion.

With the exception of the sunflowers the plants

appeared to suffer no ill effects from either the ary or

16

moist atmospheres, In the instances referred to the
Plants growing in the atmosphere saturated with moisture
were more or less distorted, the stems being somewhat
knotted or twisted. Se probable that the excessive
strain due to thé inerease in turgor, as a result of the
checking of transpiration, caused the tissues to assume
somewhat abnormal shapes.

There rAS A preceptible difference in the height of
the plants grown under the two conditions as is shown by
the figures in table IIT. Corn and sunflowers reached
their greatest height in the dry atmosphere, while peas,
wheat and buckwheat were taller where moist conditions pre-
vailed. The inerease in height was in every instance
coincident with an increase in total dry matter except in
the case of buckwheat. With the exception of corn this
game relation exists between the height and green weight.

It will be seen that the amount of water transpired
exerted a marked influence on the composition of the
plants. In every instance the percentage of water was
greater in the plants grown in the moist atmosphere. We

would expect this to be the case as the turgidity of the

17

cells, and consequently the amount of rater contained in
the tissues, would be much greater where there was but
little loss by transpiration. The percentage of ash in
dry matter also varied in the plants grown under the diff-
erent conditions.

It is significant to note that in every instance, com-
paring the plants grown under dry and moist conditions,
the higher percentage of ash in dry matter is coincident
with a lower yield of total dry matter, tho the total
amounts of ash constituents are practically the same under
both conditions. This appears to indicate that the con-
Aitions which are unfavorable for growth inhibit the elab-
oration of organic food substances to a greater degree than
the absoprtion of mineral salts.

It will be observed that transpiration was not en-
tirely checked in the moist atmosphere. This is in accor
dance with the view generally heid by plant physiologists
that, in the presence of sunlight, the temperature of the
plant usually rises ebove that of the surrounding air and
that under these conditions transpiration may be carried on

to a Slight degree even in an atmosrhere saturated with

moisture.

18

In the case of corn and wheat, more particularly the
latter, part of the water recorded under the head of trans-
piration was removed from the slants by guttation.

During their early period of growth drons of water were
often seen, in the morning, on the ends of the leaves of
those plants which were in the moist atmosphere. Toward
the latter vart of the experiment this was not noticed.

The results show very conclusively that transpiration
varies directly with the humidity of the atmosphere sur-
rounding the plants, but growth, however, does not appear
to show a similar relationship to either of these factors,
in fact the largest total yield of dry matter in three
cases out of five was where the least quantity of water
vas transpired.

If grovth were directly dependent upon transpiration,
as many of the leading plant physiologists assert, then
we would exvect to find, for each species, a constant ratio
between the increase in substance ana the water transpired
but sueh is not the case, as is shown in the last colum
of Table III and by the results of experiments conducted

along this line by certain investigators.

19

Conclusions.

The results shov that in certain of the species of
plants under investigation maximum growth may be carried
om wnen transpiration is reduced to a minimm, at least
during the early period of vegetative growth.

Where there is a decrease in growth coincident with
a checking of transpiration the decrease appears to be
due to the inhibition of the elaboration of organic matter
rather than by limiting the quantity of mineral salts
absorbed.

In general the checking of transpiration does not
anoear to decrease the total amount of mineral salts ab-
sorbed oy the plant, at least for the »veriod of growth
auring which the plants were under observation.

Tne composition of the plant is materlally affected
by vastepanie in the rate of transviration, especially the
percentages of moisture in the fresh plant and of ash in
the dry matter.

There appears to be no constant ratio between the
quantity of dry matter produced and the amount of water

transpired, the relation varying according to the envir-

20

onment of the plant.
This vork was carried on under the direction of
Professor G. F. Atkinson and lr. o. . Edgerton, to whom

I am indebted for many valuable suggestions.

Be

Se

4e

5e

21

Bibliography.

Barnes, C. Hh.

The Significance of Transpiration. Science

N. S., 25 : 460. 1902,
Gain, Edmond.

Le role physiologique de l'ean dans la
vegetation. Ann. des Sci. Nat., 7° ser. 20:
63-213. 1895.

Godlewski, T.
Studien ueber das Wachsthum der Pflanzen.
Bot. Centpl., £5 : 24 - 40. 1898.
Green, J. Reynolds.
Vegetable Physiclogy, 324, 825. 1900.
Hall, A. D.
The Soil, 84, 85. 1903.
Kreusler, U.

Ueber eine Methode zur Beobachtung der
Assimilation und Athmung der Pflanzen und ein-
ige diese Vorgaenge beeinflussende Momente.
Tagebl. der Naturforscher -— Versammlung zur

Strassburg, 539. 1885.

22

7. Lawes, J.B., and Gilbert, J. H.

Influence de la secheresse de 1870 sur les

recoltes de Rothamsted. Anne Agron., I. 251-
278. 1875.

8. Livingstone, B.%.

The Relsaticn of Transpiration to Growth in
Wheat. Bot. Gaze, 40: 178 - 195. 1905.

The nelation of Transnviration to Other Pune-
tions, BeSsRss i6 : 619. 1905.

The Relation of Desert Plants to Soil Moisture
and to Evaporation. Carnegie Institution of
Washington, Publication No. 50 ; 41. 1906.

96 Pfeffer, JW.
The Physiology of Plants, (English translation

by Asds Mwart) I : 284, 285. 1900 5 FI : 180,
1908.

10. Sachs, Julius.
The Physiology of Plants, 227. 1887.

il, Sehicesing, tl. Th.

Vegetation comparee du Tabac sous cloche et

i'air libres Anns G.801l. nat., v¥.8er., 10 ;
366-8609. 13869!

12.

14.

15.

23

Strasburger, I., Noll, ¥., Sehenck, H., and Schimper,

A.T.W. Ay Text-book of Botany, 180, 189.1898

Tschaplowitz, F.

Gibt es ein Transpirations—Optimm ?

Bot. Zeit., aot. 5 358-362. 1883.
Wolliny, ©.

Unters. ueber den Finfluss d. Luftfeuchtigkeit
auf Wachsthum. (Inaug. Diss.) Halle. See also
Bot. C6ntralbl., v6: 249. 1898.

Woods, A. Fe

Researches on Transpiration and Assimilation.

Bot. GaZes, 21 z Bon Sb. 1896.

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