SUN RAYS—ABBOT OS ae 
with blue green, another with yellow orange, another with red, and 
one is of clear glass. Thus the rays of sun and sky are modified 
by the absorption of the glass so that different regions of the spec- 
trum are most effective for the several little gardens. It is very 
curious to see the changes of color in a lady’s dress as she passes 
from garden to garden under the control of these different colored 
lights. These conditions change remarkably the character of the 
plant growth as shown by the accompanying illustrations. 
There is also a great movable roof which can be rolled over the 
hothouses. This is provided with clusters of powerful electric lamps 
sufficient to be a substitute for sunlight. With this apparatus, 
experiments in the effect of continuous and partial time illumination 
are performed. Some of the results are shown in the illustrations. 
This field has also had much attention by Doctor Garner and associ- 
ates of the United States Department of Agriculture. 
_ Everyone knows how a potato in a dark cellar in springtime sends 
out its white sprouts, which stretch away sometimes a yard or more 
toward some feeble crack of light. Here we see two things of 
importance. First, that the healthy green development necessary 
to sound growth can not take place without adequate light, and, 
second, that insufficient light leads to monstrous elongation of plant 
stems. 
In the solar chemistry of the leaves, their green coloring matter, 
called chlorophyl, seems to be indispensable. Yet it does not itself 
join permanently in the reactions, but rather seems to be what is 
called a catalyst, which in chemistry means some substance that is 
necessary to cause reactions to happen, but is not itself a part either 
of the original materials or of the end products. What must happen 
in plant chemistry is the joining of each molecule of carbonic acid 
gas with a certain number of molecules of water, and the removal 
from the mixture of one molecule of oxygen, leaving the compound 
a single stable molecule of the type called a sugar. There are many 
sugars and near sugars. Of these our ordinary cane-sugar molecule 
includes 12 atoms of carbon with 11 atoms of oxygen and 22 atoms of 
hydrogen. Much simpler sugarlike substances exist, but all, as we 
remarked above, have the general formula C,O,,H.n, where C, O, H, 
stand for atoms of carbon, oxygen, and hydrogen, and n and m stand 
for numbers which may run up nearly to a score. 
The sugars are closely allied to the starches, whose molecules 
have the same general relations of numbers of the three chemical 
constituents, but contain several or many times as many atoms as 
the sugars. Starches are stored up by the plants in great profusion 
in their roots, tubers, and fruits. They break up readily into sugars. 
Starches, sugars, and, in addition, cellulose, in whose molecules are 
also found the same general proportions of the three constituents, 
