RHYTISMA. 



243 



is completed. In the following spring, the sclerotium-spots 

 on the fallen leaves have become thicker and superficially 

 wrinkled. At this stage the apothecia are produced, and 

 dehisce by fine elongated fissures ; they contain club-shaped 

 asci and thread-like paraphyses with hooked ends. The thread- 

 like ascospores are ejaculated with considerable force, and reach 



Fig. 128. — Rhi/tisma acei-inum. Two apothecial cushions on leaf of Acer 

 campestre in first slimmer. A, Leaf-apex of Acer platanoides with the mature 

 apothecial cushions as seen in the second summer, with their characteristic 

 wavy marking, (v. Tubeuf del.) 



maturity in May or June. According to Klebahn,^ the spores 

 have a mucilaginous membrane, but this does not throw much 

 light on the problem of how they reach the leaves of trees ; 

 wind, however, would seem to be the agent for distribution. In 

 three weeks after infection, leaves show yellow spots ; in eight 

 weeks the pycnidia appear. 



^Botan. Centralblatt, Lviii. , 1894, p. 321. 



