THALLOPHYTES 



53 



by means of which the rust is carried through the winter. 

 Very naturally, the former are often called " summer spores" 

 (Fig. 35), and the latter " winter spores" (Fig. 36). 



Early in the following spring the winter spores germinate, 

 producing very short filaments, and these filaments put out 

 a few slender branches, at the tip of each of which a spore 

 is formed (Fig. 37). These little filaments that produce the 

 third kind of spore are not parasites at all, for they are not 

 related to any host. The spores they produce may be called 

 the " early spring spores." 



The early spring spores ger- 

 minate when they fall upon the 

 right kind of host plant. In 

 the wheat rust first studied in 

 England, the host plant that 

 received the early spring spores 

 was found to be the barberry. 

 The spores form an extensive 

 internal mycelium in the bar- 

 berry leaves, and this mycelium 

 sends to the surface (usually 

 the under surface) groups </ 

 sporophores with abundant 

 spores, the groups forming 

 reddish patches that some- 

 times cover the under surface 

 of the leaf (Fig. 38). This is 

 the fourth kind of spore, and 

 may be called the " spring 

 spore." 



The spring spores that fall 

 upon young wheat plants germinate and form the mycelium 

 that feeds upon the wheat, and that produces the summer 

 and winter spores with which this account began. 



In the life-history of wheat rust, therefore, there are four 

 5 



FIG. 39. Mycelium of a mushroom 

 producing sporophores (young 

 mushrooms, called "buttons"). 

 After SACHS. 



