254 LEAVES 
energy. The need of energy for photosynthesis is easy to under- 
stand. The combining of the elements of carbon dioxide and 
water into sugar is preceded by a process of dissociation in which 
carbon dioxide and probably water are in part at least separated 
into their elements. But carbon dioxide and water are very 
stable compounds, and to separate them into their atoms requires 
much energy. To force the atoms of CO, to separate requires an 
energy expressed by a temperature of 1300°C. It is obvious 
that sunlight will not decompose carbon dioxide and water; for, 
if so, these elements would be decomposed in the air. Therefore, 
the chlorophyll must change the sun’s rays into a form of energy 
which is available for bringing about these dissociations. How- 
ever, this energy consumed in bringing about these dissocia- 
tions is not lost, but is stored in the sugar as latent energy to be 
released when the sugar or the compounds formed from sugar 
are broken into simpler compounds or into carbon dioxide and 
water. Thus another relation of photosynthesis to respiration 
and other oxidation processes now appears. Fhotosynthesis 
stores the sun’s energy in chemical compounds which, when 
broken into simpler compounds by respiration, become a source 
of energy for all other plant or animal activities. It is also the 
sun’s energy that is released when coal, wood, oil, and other plant 
or animal products are burned. Thus the chloroplasts, enabled 
by their chlorophyll to utilize the sun’s energy, stand out as the 
plant structures upon which our supply of both food and energy 
depends. 
The utilization of only certain rays of the sun accounts for the 
color of leaves. When chlorophyll is boiled out of leaves with 
alcohol and the solution is viewed with a spectroscope, it is seen 
that the red and blue rays are absorbed while most of the green 
rays are allowed to pass through. This experiment demonstrates 
that chlorophyll uses the red and blue rays for energy and allows 
the green rays to escape. Thus leaves are green because from 
them only green rays come to our eyes. 
By imagining a chloroplast as a factory, the process of 
photosynthesis may be summarized in the following way: the 
chlorophyll is the machinery by which sunlight, the source of 
power, is applied to the work; carbon dioxide and water are the 
raw materials; sugar is the product synthesized; and oxygen is 
a by-product. The veins are the lines of transportation which 
