62 MICROSCOPIC FUNGI. 



the same species : the latter we have found in tlie 

 montli of May^ and tlie former in August and 

 September. The lower leaves of young seed- 

 lings have generally rewarded us with the best 

 specimens of the septate-fruited brand {Puccinia 

 variahilisy 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. 88)^ 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 {Garduus lanceolatiis) . 

 This latter plant is exceedingly abundant^ and so 

 is its parasite {Puccinia sijngenesiarimi, 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- 



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