l66 BOTANICAL GAZETTE. [J u ty» 



under conditions as rigid as they could practically be made, 

 a circumstance upon which, I think, too great stress cannot 

 be laid in connection with any experimental work of this na- 

 ture. In all cases the Gymnosporangia were gathered be- 

 fore they had had an opportunity of becoming mixed ; in fact 

 before they were fully mature, and the hosts for infection were 

 in all cases potted plants, started early in the house or green- 

 house, and infected in different rooms or buildings, being 

 subsequently kept separate till all danger of accidental mix- 

 ture was past. It is hardly necessary to point out the su- 

 periority of this method over cultures made out of doors, in 

 which the possibility of error cannot be eliminated ; but by 

 far the most crucial test in such cases is gained by forcing 

 the fungus as well as its host so as to make the infection a 

 month or more before it would naturally occur out ot doors, 

 as was done, for example, in the second culture of G. globosum 

 given below. In this way the sources of error are reduced 

 to zero if, as in this case, only one species of Gymnosporan- 

 gium is used. As in my previous cultures, I have found it 

 more convenient to place the spore masses directly upon the 

 sprinkled leaves, as soon as the sporidia begin to form, and 

 to keep the plants covered with bell glasses or wet paper for 

 one or two days, carefully removing the jelly as soon as 



these were taken off. 



CULTURES OF 1887. 



G. MACROPUS. 



March 1. Sporidia sown on 



2 Pyrus Malus, 



both host and fungus having been forced in a greenhouse where the sub- 

 sequent development was watched. 



March 10. Spermogonia appeared abundantly on both plants, from 



which one recovered while the other 



May 1, produced secidia of Rcestelia pyraia. 



G. CLAVARIiEFORME. 



April 24, sporidia sown on 



2 Amelanchier Canadensis. 

 April 27, sporidia sown on 



1 Amelanchier Canadensis. 



1 Crataegus coccinea. 

 May 1. Spermogonia appeared on the two first Amelanchiers, which 



were much distorted. 



May o. Spermogonia on the second Amelanchier. No result with 



the Craingus. 



