THE IMPORTANCE OF PHOTOSYNTHESIS 279 
(1) some of it is digested in leaves and built up into new 
protoplasm; (2) some of it is stored in the leaves to be 
used later; (3) another portion is stored in other parts of 
the plant, as in the potato, in seeds, buds, and roots. 
Comparison . — The process of photosynthesis may be 
compared to any other manufacturing process which requires : 
1. A factory — in this case, green leaves. 
2. Machinery — the plant cells containing chlorophyll. 
3. Power — light from the sun, a form of energy. 
4. Raw materials — carbon dioxide and water, and small 
portions of nitrogen and other chemical substances which are 
dissolved in the water taken in by the roots. 
5. Working hours — daylight. 
In this comparison the products are the carbohydrates and 
other forms of food which are made from them, and the 
by-product, oxygen. This manufacturing process disposes 
of its products (1) by storing them on the premises, the 
leaf; (2) by using them on the premises, digesting them 
to make more protoplasm; (3) by sending them away to 
other parts for storage, or immediate use; (4) by using 
them to make other food substances, namely, proteins, and 
fats or oils. 
245. The Importance of Photosynthesis. — The impor¬ 
tance of photosynthesis cannot be overestimated. It is the 
only natural process in the world by which raw material can 
be changed into food and by which energy can be stored up 
for future use. The plant makes use of this stored-up energy 
to produce new leaves, flowers, etc. Animals, which have 
not the ability to manufacture food from raw materials, 
depend directly or indirectly upon green plants for their 
supply of food. Besides making all the vegetable food in 
the world, plants, in using the carbon dioxide produced by 
animals, keep the air free from excess of it and so make it 
safe for animals to breathe. They also, by the same pro¬ 
cess, keep it well supplied with oxygen. Photosynthesis is 
