SORI AND SPORE FORMS 315 



3. Mycelium perennates and produces teliospores in the spring 

 in Gymnosporangium spp. Such teliospores germinate immedi- 

 ately in situ, and the sporidia are dispersed to infect the alternate 

 host. 



4. Aecial mycelium hibernates, that of Coleosporium for 1 

 year, of Cronartium for several years. Aecia appear in the 

 spring, and aeciospores infect the telial host. Teliospores are 

 formed during the summer that infect the aecial host immedi- 

 ately, and aecial mycelium again hibernates. 



5. Both aecial and telial mycelia perennate. In spring aecia 

 arise from mycelium, and the aeciospores infect the telial host. 

 From telial mycelium teliospores also form in the spring, which 

 germinate immediately, and the sporidia initiate infection of the 

 aecial host. Urediniospores arise in the summer from the same 

 mycelium as bore teHospores. Example: Melampsorella caryo- 

 phyllacearinn. 



6. Both urediniospores and teliospores form in the late sum- 

 mer. The teliospores germinate immediately and infect Anchusa, 

 upon which pycnia and aecia form. The aeciospores can infect 

 rye during the autumn, but it is not known whether the uredinio- 

 spores can survive the winter. Example: Fiiccinia dispersa. 



Sori and Spore Forms 



Pycnia or spermogonia. In the usual course of events, pycnia 

 are the first structures formed as the result of infections initiated 

 by basidiospores. Moreover they usually precede the aecia but 

 may be formed simultaneously with them. Arthur (1904) re- 

 gards them as of importance in foretelling the length of the de- 

 velopmental cycle. Pycnia do not repeat themselves but occur 

 only once in the life cycle. If pycnia and urediniospores arise 

 from the same mycelium, aecia are absent from the cycle. If 

 pycnia and teliospores are associated, neither aecia nor uredinia 

 exist in the cycle. Occasional species exist, such as Uromy- 

 cladium maritinnnn, U. notabile, and U. robinsoni, in which the 

 pycnia are associated with both uredinia and telia. If the telio- 

 spores germinate immediately upon becoming mature and pycnia 

 are associated with them, other spore forms are absent. In Piic- 

 cinia malvacearinn on various mallows, Alelampsora farloivii on 

 Tsiiga canadensis, Gallowaya pinicola on Pimis virginiana, 



