OF ARTS AND SCIENCES. 71 



changing my opinion with regard to the harmlessness, practically speak- 

 ing, of the Peronospora in New England. I never meant to deny that, 

 theoretically speaking, the existence and growth of a parasite like 

 P. viticola would weaken the vines in which it was growing ; but the 

 fact is that I have repeatedly seen vines attacked by the Peronospora 

 produce good crops of grapes year after year, and, whatever we might 

 expect in theory, in practice no perceptible harm is done to the open- 

 air grape culture in New England. In that region, as was stated in 

 the Bulletin, the great danger to be dreaded is the occurrence of frosts 

 before the grapes have ripened, and the Peronospora, in so far as it 

 causes the leaves to curl up, thus exposing the grapes to the full force 

 of the September sun, benefits rather than injures the grape crop. 

 The position of New England and the northern parts of the United 

 States with regard to grape culture is quite exceptional, and there is 

 evident reason why what is true of the Peronospora here should not 

 be true in other parts of the world. 



Nos. 209 and 210. Peronospora Halstedii, Farlow. This species 

 was referred to in the Bussey Bulletin, Vol. TI. p. 235, January, 

 1878, where mention was made of a Peronospora found by Mr. B. D. 

 Halsted on Eupatorium purpureum, near the Bussey Institution, in 

 May, 1876. Since then the fungus has been collected in numerous 

 other localities and on several different hosts, and it may now be 

 reo-arded as one of our most widely spread and characteristically 

 American species. It was found by Professor Bessey, in August, 

 1878, on Eupatorium purpureum, Bidens frondosa, and Rudheckia 

 lacmiata, and since then it has been observed by Professor Arthur on 

 Helianthus doronicoides in Iowa ; on Helianthus strumosus and Sil- 

 phium terehinthinaceum in Wisconsin, by Professor Trelease ; on 

 Helianthus tuberosus in West Chester, Pa., by Mr. J. B. Ellis; and I 

 have myself also found it on Ambrosia artemisicEfolia in several dif- 

 ferent localities. In short, we may expect to find it on almost any 

 Composite, although it apparently affects principally the Tubidljiorce, 

 while with us P. (jangliformis affects rather the Ligulijlorce. The ripe 

 oospores of P. Halstedii are not common, as far as my experience 

 goes ; but I have seen them in good condition on the leaves of Heli- 

 anthus doronicoides, collected at Charles City, Iowa, by Professor 

 Arthur. The conidia vary in their development according to the 

 host, forming large and conspicuous patches on Rudbeckia, Silphium^ 

 and Helianthus tuberosus, but rather inconspicuous spots on Ambrosia. 

 The conidial spores vary very much in size, and their shape, as in all 

 Peronosporce, depends much on their age ; when young oval, when 



