RHYTISMA. 



243 



is completed. In the following spring, the sclerotiuni-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.— JihT/tisma acei-imou. Two apothecial cushions on leaf of Acer 

 campestre in first summer. A, Leaf-apex of Acer platanoiJe» with the mature 

 apothecial cushions as seen in the second summer, with their chai-acteristic 

 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. CentrcUhlatt , lviii., 1894, p. 321. 



