Erysiphe 185 



forms a quite similar state to that of E. liriodcndri and more- 

 over quite commonly on TJialictnun minus, Polygonum avlculare, 

 etc. E. polygoni shows a tendency towards developing a persistent 



mycelium. 



More marked than E. linodcndri is a form on Diennlla 



Japonica from Sapporo, Japan (K. Miyabe and N. Hiratsuka) sent 



to me by Professor Miyabe under the mss. name of Erysiphe 



dicrvillae, with these notes, " E. diervillae ripens its perithecia only 



in the early spring of the next year. Mycelial layers are formed 



on the young branches and persistent capsules. Perithecia i. 



O- 



135/^, asci 37-45 X 67-86/^, ascopores {(i--]) n X 22 /i." This 

 form on Dicrvilla covers the stem and fruit of the host-plant with 

 soft dense patches of persistent mycelium, in which the perithecia 

 are more or less imbedded. Except in these characters, however, 

 the fungus is not different from E. polygoni, and it is to be noticed 

 that here and there on the stem, perithecia occur from which the 

 mycelium has almost or quite disappeared, and so are more or less 



naked as in ordinary E. polygoni. 



Even more striking is the plant published by Berkeley as 

 Erysiphe dcnsa, on Aristotelia racemosa from New Zealand. 

 Berkeley remarked : " This differs from E. Martii Lev. merely in 

 its thick persistent mycelium, which gives it a very lichenoid ap- 

 pearance, especially when on the upper surface of the leaf" There 

 is a fine series of " E. dcnsa " in the Kew Herbarium, and the 

 specimens show in a very clear manner how variable the nature of 

 the mycelium is in the present species, even on the same host- 

 plant. In this series, the mycelium on most of the leav 

 dense and compact, more or less thick, and lichenoid, cither 

 limited to spots or extending more or less completely over the 

 whole upper surface of the leaf The fungus in this condition 

 seems quite distinct from E. polygoni, in which a persistent lichen- 

 oid mycelium has not been recorded on any host. On other 

 leaves of Aristotelia in this series, however, we find only a thin 

 layer of persistent mycelium, from arachnoid to merely pruinose 

 in consistency. Finally, on some leaves we find an absolutely 

 evanescent mycelium. I can find no difference in the perithecia 



ery 



polyg. 



consider- 



ing 



the variable nature of the mycelium, I do not think E. 



