230 ELEMENTARY SCIENCE 



sidering, which, to perceive, one must have the power of 

 sight. But even blind people could not live were it not 

 for the effect of light upon green leaves. For every man 

 must have food, and the basis of all food-supply is that 

 manufacture of it which goes on in green leaves when, 

 and only when, light is received by them. 



This process of food manufacture in green leaves you 

 have already learned. It is called photosynthesis, which, 

 except for its length, is a very good name for it. It is a 

 .word which explains its own meaning. The photo in it 

 means light. Syn means together. Thesis means putting. 

 So the whole word may be translated putting together in 

 the light, and it refers to the power of the plant to put to- 

 gether in the light certain substances in such a way that they 

 form food, food of the class known as carbohydrates, of which 

 starch and sugar are examples. Photosynthesis is not 

 all that there is to food making. The food which is made 

 by photosynthesis may be afterward transformed into 

 other kinds of foods. But photosynthesis is the only 

 process by which food is made out of materials which are 

 not themselves food. We ourselves have the power to 

 transform foods from one kind into another, but we do 

 not have the power to make food out of materials which 

 are not food. This is done only by green plants. In the 

 foods which they manufacture they store up energy which 

 is derived from sunlight. 



