OP ARTS AND SCIENCES. 319 



The sporidia of G. macropus, when sown, were followed by spermo- 

 gonia on apple seedlings, on seedlings of Crat(Egus Douc/lasii, and on 

 leaves oi Amelanchier. As distinguished from the last species, where 

 the spermogonia appeared most abundantly on species of Cratcegiis, the 

 present shows the growth of spermogonia on apples and Amelanchier, 

 and less abundantly on Cratcegus. G. clavipes was followed by sper- 

 mogonia on apple seedlings, but not on Amelanchier. "With what two 

 Roestelice the two last-named Gymnosporangia might be associated one 

 cannot safely guess. Considering the distribution in nature, one would 

 be inclined to suggest R. transformans * as belonging to G. clavipes, 

 and some form of R. lacerata or R. penicillata as belonging to G. ma- 

 cropus. But it is well not to encroach upon the boundaries of pure 

 imasfination. 



Rejecting what I have called my third series of cultures on shoots 

 of Amelanchier and P. arhutifolia, on the ground that they were 

 conducted under conditions not conducive to accuracy, — which I 

 consider to have been the case, — and assuming that the (Jratcegus 

 tomentosn employed in cultures previous to 1883 was already in- 

 fected with a Rosstelia when the experiments began, — which might 

 or might not have been the case,t — the conclusions to be drawn 

 are, that, — 



1. The fecidium of G. biseptatum is probably Rcestelia hotryajntes. 



2. The cecidium of G. glohosum^ to be kept distinct from G. fuscum^ 

 is possibly Rcestelia aurantiaca. 



3. The a?cidium of G. macropns is to be sought among the Rces- 

 ielice growing especially on apples and Amelanchier. 



If it be admitted that the O. to?nentosa was not previously infected, 

 but that the development of spermogonia was the result of the sow- 

 ings, then it follows tliat the sporidia of our four species in question 

 may produce spermogonia indiscriminately on one and the same host, 

 or on different hosts, in a way Avhich is not paralleled in nature by 

 the species of Roesfelia. There is nothing impossible or illogical in 

 this conclusion ; but in accepting it we must bear in mind that we 

 must reject the observations of Oersted, and all who have only suc- 

 ceeded in developing spermogonia without tecidia, but have neverthe- 



* G. clavipes has been found by Holway in Iowa, and Trelease doubtfully 

 refers to R. transformans a spermogonial form, whose ajcidia were not seen, 

 found on P. arhutlfoUa in Wisconsin. There is need of further information as 

 to the western limits of botli these forins. 



t See my paper on Gymnosporangia, pp. 36, 37. . 



