LEAVES 21 
ing over the plants a large funnel and leading the bubbles 
into a test tube, in which the presence of oxygen can then 
be tested. 
It has been noted that photo- 
synthesis is associated not mere- 
ly with light but also with green 
tissue ; and in examining the 
structure of the leaf it was dis- 
covered (§ 13) that the green 
color is due to the presence of 
chloroplasts in the mesophyll 
cells. It is these chloroplasts 
that manufacture the carbo- 
hydrates, and they obtain from 
the light the power (energy) to. Ti.15-8 bea laf whore termi 
do it. The first visible product whose lateral leaflets have been 
of photosynthesis is starch, and SP ose to Hight; the test shows 
when the working cells are very former and an abundance of it 
‘ in the latter. 
active starch may be observed 
to accumulate in them; but when the process becomes 
slower or stops, as during the 
night, this starch disappears, the 
food being carried away for use 
(Figs. 15 and 16).* | 
A summarized statement of 
photosynthesis is as follows: It is 
the manufacture of carbohydrates 
, by chloroplasts in the presence of 
Fic. 16.—A geranium leaf, one. light, water and carbon dioxide 
half of which has been cov- being used, and oxygen being 
ered; the test shows absence 7 
of starch in the covered half. given off as a waste product. 
* Experiments should be devised to test for the accumulation of 
starch in leaves that have been exposed for some time to a strong light, 
and to show that this accumulation does not take place in the dark. 
In the experiments illustrated by Figs. 15 and 16, the test for starch was 
