31G PROCEEDINGS OF THE AMERICAN ACADEMY 



striking JEcidlum Nescea Gerard. No spermogonia, however, were 

 developed. At the date wheu the culture was started the leaves of 

 Nescea were not fully expanded ; but they soon opened, and the shoots 

 grew rapidly in the house. 



In attempting to draw any conclusion from the statements previously 

 given, we may exclude any consideration of G. Ellisii, for neither in 

 1S83 nor in previous years did spermogonia appear in any cultures 

 made with that species. The species used include all the members of 

 the genus Gymnosporangium known in the Eastern United States ex- 

 cept (x. davariceforme DC, of which I could not procure fresh material 

 in season, G. conicum DC, and the typical form of G. fuscum DC 

 The last two forms require further study, and it is not certain that the 

 few specimens referred to them should not be placed in other species. 

 The results of the cultures may be summarized as follows : — 



Spermogonia appeared after sowing the sporidia of 



G. fuscum var. ghhosum on seedling apples, on CratcEQUS oxy- 

 acantha (very abundant), on C. JDoufflasii, and on apple 

 leaves under bell-glass. In cultures of previous years, also 

 on C tomentosa. 



G. macropus on apple seedlings, on C. Douglasii, and on shoots of 

 Pyrus arhutifulia and Amelanchier. Also in previous cul- 

 tures on C. tomentosa and Amelanchier. 



G. clavipes on apple seedlings and shoots of Pyrus arhutifoUa and 

 Amelanchier. 



G. bisrptatitm on Amelanchier leaves and shoots, and previously on 

 C. tomentosa^ 



From the above it will be seen, not only that the sporidia of differ- 

 ent species Of Gymnosporanginm when sown on the same host-species 

 were followed by the appearance of spermogonia, but also that the 

 sporidia of each species was followed by spermogonia when sown on 

 several different host-species. The perplexity is all the greater, be- 

 cause the host-plants as a rule are species wdiich, in nature, are attacked 

 by more than one Rcestelia, and in the case of the cultures the species 

 could not, of course, be determined by the spermogonia above. In this 

 connection, a word may be said on the production of iccidia by cultures. 

 In the case of leaves kept on slides under glasses, it is of course out of 

 the question to expect to be able to keep the leaves free from mould 

 long enough for a}cidia to develop. For tentative experiments, where 

 one wishes to form some notion as to the probability of the connection 

 between certain forms, they do very well. But it may be asked why 



