V. The Intluence of Light upon the Growth of Leaves. 
121 
bore no leaves, but at the conclusion, it possessed six normal leaves 
and six tendrils. The length of the langest Segment of the largest leaf 
was five centimOtres. A careful examination of these leaves shevved that 
no starch could be detecled in their cells by nieans of the well-known 
method vvilh alcohol, potash, and solulion of iodine, excepting only in the 
guard-cells of tlie stomata, whereas starch existed abundantly in the ine- 
sophjll of a leaf vvhich had not been covered by the bell-jar. 
Ihese Experiments prove that leaves can be developed and can grow 
under circumstances which prevent assimilalion, if it be admitted that the 
blue, indigo, and violet rays are incapable of causing assimilalion. The 
expert men ts of Sachs 1 ) however, shew that although this function is almost 
entirely suppressed when the plant is exposed to blue light, yet it con- 
tinues lo some exlent. This is confirmed by the observations of Kracs 
on Spirogyra 2 , Funaria, and Elodea. It will be at once suggested by 
those who hold the theory of »self-nutrition« of leaves, that in my ex- 
perimenls assimilalion must have occurred just sufficienlly to provide for 
the nutrition of the growing tissues, so that there was no formation of 
an excess of carbohydrales vxhich might be deposited in the chlorophyll- 
gratns in the form of starch. This explanation is evidenlly strained, for 
it is highlv improbable that the amount of carbohydrales thus produced 
would suffice to Support the growth which took place in these leaves. It 
's more natural to conclude that the amount of assimilalion which took 
place was so trifling as scarcely lo merit consideralion, and (hat the ma¬ 
terial necessary for the growth of the leaves was obtained front other 
parts of the plant, as is the case in these leaves which attain a con- 
siderable size when growing in complete darkness. 
II. Growth ol plants in air containing no C0 2 . 
In these experiments I used seedlings as well 
In the first series the method was as follows. Seeds 
of Cucurbita pepo were sown in a mixture of sand 
and mould, and, after germination, the young plants 
"eie allowed lo grow unlil the hypocotvledonary por- 
tion of the stem had attained a length of two or three 
inches, and the cotyledons had become green. The 
most vigorous one was then selected and cul off at 
the level of the earth. Its stem was then placed in a 
small glass containing a dilule solution of potassium 
nitrate, the glass was set on a saucer containing eon- 
centraled solution of eaustic potash, and the whole 
as mature plants. 
Fig. 2. 
C Handbuch der Experimental-Physiologie, p. 27. 
2] Jahrb. f. wiss. ßot. Vit. 18S9—7i). 
