THE DISEASES OF CONIFERS. 



147 



Eosaceae — e.g.y Pear, Hawthom,Mountain Ash, Service-tree, &c.— 

 present a totally different appearance ; these rocidial forms on 

 the Eosaceae received the name of Bo^stelia. 



Various " species " have been described of both. Besides 

 this, Farlow has investigated a number of American forms, found 

 on Cupressineffi and Eosaceae in the United States.* 



A number of careful experiments have been made in this 

 country by Mr. Plowright, one of the best authorities in 

 England on the Uredineffi, and he came to the conclusion that 

 about four species of Gymnosporangium may be upheld as far as 

 this country is concerned. These species occur on J. Sabina 

 and the Pear ; J". Sabina and the Hawthorn and others ; J". 

 communis and Hawthorn, &c. ; and J. communis and the Moun- 

 tain Ash. 



But Mr. Plowright's cultures, like those of others, suggested 

 that much difficulty is incurred in attempting to keep the forms 

 distinct ; and with the caution of a true scientific man, Mr. 

 Plowright, in one case at least,t suspected he had perhaps used 

 mixed Teleuto-spores, instead of concluding on insufficient evi- 

 dence that the Teleuto-spores of Gymnosjoorangium SabincB infect 

 both the Pear and the Hawthorn ; perhaps it was less commend- 

 able on Mr. Plowright's part to form a new species {G. confusum), 

 though at the same time it is difficult to see how he should 

 avoid it without much further research, and only those who 

 have had much experience know how troublesome such in- 

 vestigations are. 



The results of such infection-experiments from various 

 sides were to arouse suspicions as to the autonomy of some of 

 the species, though some of the main points were confirmed by 

 all. Credit is due to Mr. Plowright for establishing the con- 

 verse culture of the ^cidio-spores on the Juniper, in the case of 

 G. clavarieforme. 



Some recent experiments by Tubeuf ^ seem to have raised 

 the whole question of the species of Gymnosioorangia again, and 

 I mention this here because it seems to me of importance that 

 the question should be settled, as it affects the cultivation of 



* "The Gymnosporangia, or Cedar-Apples of the United States," Ann. 

 Mem. Boston Society of Natural History, 1880. 

 f " Brit. Uredineae and Ustilagineas," p. 233. 



X " Centralbl. f. Bakteriologie u. Parasitenkunde," B. ix., 1891, p. 89. 



L 2 



