294 GENERAL BIOLOGY 



even some of the smaller worms, also contain similar 

 algae, usually of a green color. These are called 

 Zoochlorella, and they function by synthesizing 

 carbohydrates for their animal hosts. 



Of course, plants suffer from the attacks of her- 

 bivorous animals, and not infrequently such animals, 

 if small, live on the plant upon which they feed 

 (the aphids, for example). To call this parasitism 

 would be, however, a rather forced use of the word. 

 On the other hand, animals are subject to the at- 

 tacks of multitudes of plant-parasites. These be- 

 long to the great group of the Fungi, and most con- 

 spicuous among them are the bacteria. By no 

 means all of the bacteria that live on or in the animal 

 body are disease-producing, yet the great majority of 

 diseases to which man and the other mammals are 

 subject are produced by bacteria that find entrance 

 to the body and multiply there. 



Grafts. A condition which may brcallnl artificial 

 symbiosis occurs in grafting. The graft or scion 

 is a twig or bud or some other portion of a plant which 

 is inserted into the stem of another (related) plant, 

 the stock, with which it enters into an intimate 

 physical relation, and the two behave thereafter as 

 one plant. The individual characteristics of both 

 elements are usually preserved. Thus a pear 

 graft on a quince stock produces only pears, and 

 different sorts of fruits may be grafted upon the same 

 stock. An application of this principle saved the 

 Bordeaux vineyards from extermination not many 



