THE LEAF 43 
sugars have complex molecules, however, and it would not seem 
probable that one of them is the first compound formed. Various 
intermediate compounds are postulated by different theories, but 
none of these theories is supported by sufficient evidence to 
warrant its acceptance at the present time. As the result of the 
photosynthetic process, glucose (grape sugar), which has the 
formula C,H,,O,, accumulates in the leaf, and this is generally 
regarded as the first stable product. 
If we regard glucose as the end product of photosynthesis, 
the formula for this process may be written as follows: 
6 CO, +6 H,O —> GH,,0, + 6 0,. 
This formula shows not only that glucose is formed in photo- 
synthesis, but also that oxygen is: liberated as a by-product. 
Moreover, the formula indicates that the number of molecules 
of oxygen liberated is the same as the number of molecules of 
carbon dioxide absorbed. This is approximately what has been 
observed in actual experiments. 
The water and carbon dioxide that enter the reaction are very 
stable compounds, and the liberation of the oxygen requires 
energy. This energy is supplied by light, which accounts for 
the necessity of light for photosynthesis. Light by itself does 
not, however, decompose carbon dioxide or water, so that the 
plant must have some means of applying the energy of light 
for this decomposition. The application of the energy of light for 
the separation of oxygen from carbon dioxide and water appears 
to be the function of the chlorophyll. 
In nature the light used in photosynthesis comes from the sun, 
but light from other sources can also be used. 
Chlorophyll is formed in flowering plants only in the presence 
of sunlight. This explains why the inside of the head of a cab- 
bage is white; it also explains the practice of banking celery 
in order to blanch it. 
Products. The sugar manufactured by plants serves them 
as food, from which, with the addition of materials from the 
soil, they elaborate all the complex substances found in them. 
