448 



ELEMENTARY STUDIES IN BOTANY 



fungus is a mushroom (Fig. 97), which enters the tree by its 

 spores lodging in wounds, or penetrates directly into the tree 



by way of the 

 soil. In either 

 event, the wood- 

 vessels are in- 

 vaded, and the 

 destruction of 

 wood is due to 

 the action of sub- 

 stances formed 

 by the fungus. 

 In this way the 

 various "rots" of 

 trees are brought 

 about. 



144. Control of 

 diseases. All of 

 the study of plant 

 diseases has for 

 its purpose the 

 control of dis- 

 eases. It is evi- 

 dent that this is 

 a vast and com- 

 plicated subject. 

 A great many 

 " treatments " are 

 suggested that 

 are not based in 

 knowledge; they 

 may do good, or 



they may be useless. Naturally, people use any treatment 

 that may do good, rather than no treatment at all. But as 

 the knowledge of plant diseases increases, treatments are 



FIG. 97. Tree fungus on aspen. After VON SCHRENK 

 and SPAULDING. 



