BROOKLYN BOTANIC GARDEN 
LEAFLETS 
Srries 1 Brooklyn, N. Y., June 4, 1913 Number 8 
THE WORK OF GREEN LEAVES 
Green leaves are the “laboratories” of the plant. So very 
important, indeed, is the work of manufacture there carried on 
that we may even call them the most important chemical labora- 
tories in the world. The stem part of the plant may in some 
respects be really regarded as only a subordinate structure in 
comparison with the leaves. Stems have been likened to a sort of 
clothes-line on which the green tissues are hung, and thus spread 
out and exposed to the sunlight. 
Green leaves are the food-factories of the world. All food 
comes from this food made in green leaves. All animals are 
really dependent upon plants for their food; were it not for green 
plants and sunshine working together, the food supplies of the 
world would soon be exhausted and animals would starvo. 
How is this wonderful work done ? While we know quite 
a little about the process, much remains to be found out. 
Somehow, light acts on the green color (called “chlorophyll” — 
leaf-green) of leaves and causes them to form this food. Sun- 
light is of course the best and most stimulating kind of light for 
the work of green leaves. The light of the full moon, which is 
only ruvunf that of the sun, causes such little results as to be 
hardly measurable. But strong electric light and gas light 
cause the food-making process to go on to a certain extent, espe- 
cially if the light be kept near enough to the plants. In some 
experiments carried on at Cornell University some years ago, on 
the effect of such artificial light, it was found that some plants, 
as lettuce, could be made to form food successfully by electric 
