02 MICROSCOPIC FUNGI. 



the same species : the latter we have found in the 

 month of May, and the former in August and 

 September. The low8r leaves of young seed- 

 lings have generally rewarded us with the best 

 specimens of the septate-fruited brand (Puccinia 

 variabilis, Grev.). The pustules occur on both 

 sides of the leaf, and are very small and scattered 

 (fig. 82). The spores are singularly variable in 

 form : sometimes both divisions are nearly equal 

 in size ; sometimes the upper, and sometimes the 

 lower, division is the smallest ; occasionally the 

 septum will be absent altogether ; and more rarely, 

 the spores will contain three cells. From the very 

 variable character of the spores (fig. 83), the 

 specific name has been derived. 



No species in the entire genus makes so promi- 

 nent an appearance as the one found on the radical 

 leaves of the spear thistle (Carduus lanceolatus). 

 This latter plant is exceedingly abundant, and so 

 is its parasite (Puccinia syngenesiarum, Lk.). From 

 the month of July till the frosts set in we may be 

 almost certain of finding specimens in any wood. 

 The leaves have a paler roundish spot, from one- 

 twelfth to one-fourth of an inch in diameter, on the 

 upper surface, and a corresponding dark brown 

 raised spot on the under surface, caused by an 

 aggregation of pustules, forming a large compound 

 pustule, often partly covered with the epidermis. 

 The individual pustules are small, but this aggre- 

 gate mode of growth gives the clusters great pro- 



