DISCOMYCETACEAE 



h: 



no other form of reproduction is Icnown ; hence, if diseased 

 leaves are collected and burned before the ascospores are 

 liberated in the spring, the disease will be arrested. 



Fig. 28. — Rhytisma acerinum. i, sycamore leaf with 

 Rhytisma blotches ; 2, section through a portion of a 

 black patch bearing spermatia, x 200 ; 3, ascus contain- 

 ing spores, also two curved paraphyses, x 300 ; 4, a 

 free spore, x 300. 



The following species oi Rhytisma also occur as parasites, 

 and if injury is being done, the diseased leaves should be 

 removed, to prevent inoculation the following spring : — 



Rhytisma pimctatum^ Fr., forms large black blotches, 

 surrounded by a yellowish line, on living leaves of Acei- 

 campestre^ L., A. pseudoplata7ius, L., and A. spicatum^ Lam. 

 In this species the black scab or crust is not continuous 

 as in R. acerinuffi, but consists of closely crowded small 

 pieces. 



