FOOD MANUFACTURE 33 



abundant in quiet waters, in which it is dissolved not only 

 from the air, but also from the breathing and decay of the 

 innumerable plants and animals that live in water. The 

 Algae naturally obtain it from the water in which they are 

 living; while plants living on land obtain it from the air, 

 chiefly through their leaves. The Algae need no special 

 equipment for obtaining water, for their bodies are exposed 

 to it and it enters all the cells freely ; but in the case of land 

 plants, the special equipment is usually a root system into 

 which water enters from the soil. 



An important feature of these two substances that the 

 green plant uses in carbohydrate manufacture, is that they 

 are what are called " ultimate wastes " when food is being 

 used. This phrase means that in our bodies, for example, 

 carbon dioxide and water are disposed of because the body 

 does not use them, and it does not use them because they 

 are so difficult to break up as preliminary to forming new 

 combinations. The ultimate wastes of living bodies, there- 

 fore, can be used by green plants as the raw materials for 

 the manufacture of food. From food to waste is the work 

 going on in all living bodies ; from waste to food is the added 

 work going on in all green plants. 



24. The agent. The active agent in the manufacture 

 of carbohydrates is the (ihloroplast ( 10, p. 10, and Fig. 1). 

 As the name implies, a chloroplast consists of two conspicu- 

 ous substances: (1) the living protoplasm (plastid), and 

 (2) the green pigment (chlorophyll). They can be separated 

 from one another by soaking green parts (as leaves) in alcohol, 

 which extracts the chlorophyll and leaves the plastids color- 

 less. Just what each of these substances does in the manu- 

 facture of carbohydrates is not known with certainty, but 

 it is certain that both are necessary. The plastid is alive 

 and the chlorophyll is not, but since the manufacture of 

 carbohydrates is a chemical process, the chlorophyll may be 

 the cause of some of the changes. In fact, a chloroplast 



