NUTRITION 43 



parts of the great work of nutrition, and they are com- 

 mon to all living things. They are among what are known 

 as the " general " life processes. 



C. Photosynthesis. — The process by which plants manu- 

 facture food out of substances which are not food occurs 

 only in the presence of light. (You see now why green 

 plants cannot live in the dark, and why leaves turn to the 

 light.) This process is called photosynthesis. Except for 

 its length, photosynthesis is a very good word. It is a 

 word which explains its own meaning. The photo in it 

 means light. Syn means together. Thesis means put- 

 ting. So the whole word may be translated putting together 

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

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

 form food. Photosynthesis is not all that there is to food 

 making. The food which is made by photosynthesis may 

 be afterwards transformed into other kinds of food. 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. 



Thus we see that, so far as the general features of nutri- 

 tion are concerned, there is but one in which plants are dis- 

 similar from ourselves. They are dissimilar from us in 

 that they possess one more nutritive power than we possess, 

 and that power is extremely important. It is a power 

 which makes us absolutely dependent upon them. It is a 

 power which green plants alone of all living things possess. 



