162 PRINCIPLES OF FARM PRACTICE 





 fungi must get such substances already made. Some of 



them molds, mushrooms, puff balls, and species of bacteria 

 - rely upon dead material, such as the remains of other 

 plants, for their supply of food material. Others rusts, 

 smuts, mildew, blights, and other kinds of bacteria satisfy 

 their needs by attaching themselves to other living plants. 

 These latter are called parasitic fungi, and the plant that 

 gives them a living is called the host. Since a parasitic 

 fungus deprives its host of starch and other food material, 

 and makes harmful poisons, it weakens and otherwise injures 

 the host, thus producing conditions known as disease. 



In order to understand how these injuries are made and 

 how disease spreads from one plant to another, it will be 

 necessary to consider how fungi grow. 



How fungi grow. There are two essential parts of most 

 fungi: One, the food-getting part, is composed of a net work 

 of fine threads or tubes, called the mycelium, which usually 

 penetrates the food substance on which the fungus grows. 

 The other, the reproductive part, is composed also of fine 

 threads which bear small bodies called spores. The spores, be- 

 ing light, are easily blown about by the wind or being sticky 

 are carried by insects, animals, or water to different places, 

 where, if conditions are favorable, they develop into plants 

 like the ones that produced them. Sometimes the spores 

 are borne free at the ends of the spore-bearing threads, and 

 thus are easily transferred from the parent fungus to other 

 places, ready to start new fungus growths. Sometimes they 

 are enclosed in cases. In this instance, the walls of the case 

 break when the spores are ripe, thus releasing them for dis- 

 tribution. 



Bacteria have already been described in connection with 

 the soil, but should be considered here with fungi, since they 



