54 ELEMENTARY STUDIES IN BOTANY 



kinds of spores, three kinds of mycelia (two of which are 

 parasitic), and two different hosts. This probably represents 

 the most complex life-history of a fungus, and illustrates the 

 great difficulty of studying and combating the rusts. Of 

 course, the rusts that attack the wheat fields of the United 

 States do not use usually the barberry as the " intermediate 

 host," since with us barberry bushes are not common enough 

 to serve such a purpose. But our several kinds of rusts use 



FIG. 40. A common edible mushroom ; really a sporophore. 



other intermediate hosts, which are plentiful enough to in- 

 sure a continuation of the rust. 



Mushrooms. Even a very short account of Fungi would 

 be incomplete without some mention of the mushrooms, 

 which are perhaps the Fungi best known to most people. 

 There is no difference between mushrooms and toadstools, 

 except that the latter name has been applied to those mush- 

 rooms that are poisonous. Very closely related mushrooms 

 may differ in this particular, so that the two names cannot be 

 used as terms of classification. For example, Boletus edulis, 



