314 COMPARATIVE MORPHOLOGY OF FUNGI 



Rhijtisma acerinum causes the tar spot of maple ; the biological form 

 platanoides (K. Muller, 1913) lives mainly on A. platanoides, less on A. 

 platanus and A. campestris; while forms Pseudoplatani and campestris 

 are specialized on A. Pseudoplatanus and A. campestris. 



Because of the obscure character of the Phacidiales, we will mention 

 only that several forms, as the above Coccomyces hiemalis, C. lutescens 

 and C. prunophorae on cherries and plums (Higgins, 1914) and Phacidiella 

 discolor, the cause of a canker of the apple in the Caucasus (Potebnia, 

 1912) form both macro- and microconidia in acervuli. In the latter 

 species, the hyphae may develop sprout mycelium under certain con- 

 ditions of growth. 



