74 PROCEEDINGS OP THE AMERICAN ACADEMY 



species of orders as remote as Geraniacece and UmbelHfercB, in their 

 sense, at least, P. Geranii must be considered peculiar to America. 

 I once tried without success to cultivate it on an Umbellifer, but that 

 hardly shows anything, as under all circumstances — and I have tried 

 many times — the couidia of this species are with difficidty made to 

 germinate at all. One naturally asks why it is that such a large pro- 

 portion of our species produce zoospores instead of direct germinal 

 tubes. From their close resemblance one might suppose that P. viti- 

 cola, P. Halstedii, and, to stretch the matter somewhat, possibly P. 

 Geranii, were derived from some common American ancestor which 

 produced zoospores. If, in the various surviving species, we find this 

 common peculiarity of germination preserved, we ought certainly to 

 suppose that this form of germination is especially adapted to the 

 climatic and hygrometric conditions of our country. Strange to say, 

 the contrary appears to be more probable. Our climate is a continental 

 one, subject to extremes of heat and moisture, and one would suppose 

 that a species with spores so contrived that they could push forth 

 germinating tubes would be more likely to survive in comparatively 

 dry seasons than one arranged to give out a number of zoospores ; for 

 it is the result of my experience that the tube-producing spores retain 

 their vitality for several days, whereas those which produce zoospores 

 lose their power of germinating in a comparatively few hours after 

 maturing. It may be said, on the other hand, that the chances of 

 survival are greatest if the spores usually produce zoospores, but in 

 exceptional cases produce germinal tubes. P. infesians, which usually 

 produces zoospores, is known occasionally to produce tubes, but of the 

 hundreds, or even thousands, of germinating spores of P. viticola and 

 P. Halstedii I have seen, I never met with one producing anything 

 but zoospores. 



No. 228. JEcidhim Convallarice Schm. var. Lilii. This was found 

 in June efrowiu^ on cultivated Lilium candidum, but was not followed 

 by any uredo or teleutospores. It certainly is not JEcidium Liliacearum 

 Ung., which is associated with Uromyces Liliacearum Ung., nor the 

 ascidium of Puccinia Liliacearum Duby, but rather a large form of 

 ^c. Convallarire Schm., of which no. 229 on Polygonatum is the 

 more common form. 



No. 230. This is the common form of ^c. myricatum Schw. 

 The small form distributed with Cent. XI. is only known to me from 

 Mr. Ellis's specimen. 



No. 225, It is possible that there was a mixture of two species un- 

 der this number, as in my copy I notice one leaf with j^c. punctatum P. 



