process in the chemical laboratory, but it takes a green leaf, 
acted on by sunshine, to do the whole of it. 
There are other very important processes going on in the leaf 
laboratories. As long as the light strikes the leaf, the above 
process goes on; and at the same time, oxygen is thrown off from 
the green tissues. The taking out of the carbon dioxide as well 
as the adding to the air this oxygen, by green leaves, helps to 
purify the air and make it fit tor animals to breath. Everyone is 
familiar with the fact that green water plants are necessary in an 
aquarium, for the gold fish or other animal life will die if not sup- 
plied with plenty of oxygen. 
Now, oxygen is given off and carbon dioxide is absorbed by 
plants only in the daytime. Both day and night, however, thejr 
must breathe, or, better, respire. That is, all the living cells, of 
roots, stems and leaves, are constantly taking in oxygen and giv- 
ing off carbon dioxide, just like animals and, in fact, as all living 
things must do in order to live. When a person says that plants 
and animals are justihe opposites of each other in theseprocesses, 
they are really telling only a half-truth. For, all plants carry on 
respiration, just like animals, all the time, both day and night. 
Of course plants do not forcibly draw in the air as wedo into the 
lungs, but they would soon die if their pores and moist surfaces 
were thickly covered with vaseline or seme such substance 
which would prevent them from breathing in oxygen. It is only 
those plants which are green which, during the daytime only, 
carry on an extra process possessed by no animal: that of taking 
in carbon dioxide and giving off oxygen under the influence of 
light. Mushrooms, which lack the green, have onl}'- the animal- 
like process, and not the extra one. 
Other complicated foods than starches and sugars are also 
formed in the green leaf laboratories. Starch forms a starting 
point for that important class of food substances called the 
proteins, the muscle and nerve forming foods. As stated above, 
we may really regard the food made by green leaves as the start- 
ing point of all food, both animal and vegetable. 
Green leaves also evaporate water, for the most part through 
tiny mouth-like openings called stomata. The evaporation from 
a young, vigorous beech tree has been calculated to average dur- 
ing the summer months nearty 20 gallons of water a day. At this 
