438 FUNGOUS DISEASES OF PLANTS 



three forms, together with one discussed by Klebahn as Melanip- 

 sora Rostrupii Wagn., all agree in having more or less spherical 

 uredospores, and in no case are there marked morphological dif- 

 ferences in the uredospores or teleutospores within this group. The 

 caeoma stages have, however, been determined, for these forms, to 

 occur respectively upon Pinus, Larix, Chelidonium and Corydalis, 

 and Mercurialis. For our purpose, it does not matter particularly 

 whether these forms are considered a group of closely related 

 species, or merely well-established physiological forms of a single 

 variable species. In Europe these are found chiefly upon Populus 

 tremula and Populus alba. In the United States it would seem 

 difficult at the present time to name the hosts positively, although 

 Populus tremuloides may be specially mentioned. 



