98 
WORLD OF INVISIBLE LIFE 
What ma\es 
leaves green? 
midrib and other ribs. All the cells are lined 
with a transparent, slimy material like the white 
of an egg. It is called protoplasm. This pro¬ 
toplasm is one of the most important substances 
in plant life, for it is the bearer of life itself. It 
is found in all living things, and while its action 
is still very mysterious to us, it is essential to 
the life processes. 
Besides the protoplasm, the cells of the leaves 
are filled with water. Embedded in the proto¬ 
plasm we can see innumerable tiny green grains, 
which are the substance which give the leaf its 
color. Each grain, under a more powerful mi¬ 
croscope, looks like a tiny sponge dipped in 
green oil. This green coloring is necessary for 
the manufacture of all the food and building 
material of the plant—the starch and sugar and 
cellulose on which man and animals live. They 
are produced in these green grains from water 
and the carbon dioxide in the air with the help 
of sunlight, which furnishes the energy for the 
process. The leaf is the factory in which the 
whole plant is made and therefore the most im- 
