THE LEAF 225 
in weight and, so the process is constructive in character. In 
photosynthesis, sunlight is the power, the chloroplasts the work- 
ing machinery or energy transformers, the chlorenchyma cells 
the factories, CO. and H,O the raw materials and glucose, 
starch or oil the finished products, while oxygen is a waste 
OXYGEN 
CARBON DIOXIDE 
~ MINERAL SALTS 
WATER 
Fic. 154.—Diagram of photosynthesis. (After Atwood.) 
a is 
<— GLUCOSE 
ipsam 
product. The production of glucose may be represented by 
the equation: 
6H2O + 6CO, + light = C.H,.0, + 602 
AssIMILATION is the process of converting food material into 
protoplasm. The chlorenchyma cells of the leaf synthesize 
proteins from the carbohydrates. In this process molecules of 
glucose derivatives containing CHO are united with nitrogen 
absorbed from the soil as nitrates to form amino acids. The 
amino acids combine to form polypeptides which are later built 
into simple proteins. The simple proteins are joined with sulfur 
or phosphorous or both to form complex proteins. ‘The latter 
enter into the formation of protoplasm. 
REsPIRATION is the process which takes place in all living 
plant and animal cells whereby complex carbon compounds 
are oxidized with an accompanying release of energy. In 
higher green plants oxygen is taken in through the stomata of 
leaves, lenticels of stems, and root hairs. It passes into the 
intercellular-air-spaces which communicate with each other 
