240 PHYTOPATHOLOGY [VOL. 6 



SUMMARY 



Although not definitely proved, it is highly probable that Peridermium 

 harknessii is identical with P. cerebrum. In California Peridermium 

 harknessii and Cronartium Quercuum are to a high degree independent 

 of each other. 



The so-called Peridermium harknessii can be transmitted directly 

 from pine to pine by infection with aeciospores, at least on Pinus radiata; 

 in nature this probably takes place through the agency of insecte. The 

 heteroecism of Peridermium harknessii on Pinus radiata is, therefore, 

 facultative. By analogy it is highly probable that the same facultative 

 heteroecism occurs in Pinus contorta and perhaps also in the other hosts 

 of the so-called Peridermium harknessii. 



Cronartium Quercuum overwinters on Quercus agrifolia; new uredinio- 

 spores form in spring around the old, dead sori on old living leaves and 

 infect the young leaves. The heteroecism of the Cronartium also is 

 facultative. 



OFFICE OF INVESTIGATIONS IN FOREST PATHOLOGY 

 BUREAU OF PLANT INDUSTRY 

 SAN FRANCISCO, CALIFORNIA 



