﻿528 Dodge: Effect of host on Gymnosporangium 



time of inoculation, May 6, the leaves were well out. A few 

 infected areas appeared May 25 but no "subicular hypertrophies, " 

 projections, or aecidia subsequently developed. Similar root 

 sprouts of Amelanchier Amelanchier and A. intermedia from the 

 New York Botanical Garden were used in numbers 243 to 246, 

 and 255. Spermogonia appeared on several in each case except 

 in number 255, but the only one to mature aecidia was number 246. 

 On June 4 hypertrophies were visible, which possessed character- 

 istics quite different from those formed on the Aronias. At each 

 point of infection on the Amelanchier leaves there were from two 

 to six separate galls which grew to be about one or two millimeters 

 high by July 22 as shown in Fig. 20. During the next three weeks 

 the tubercles elongated slightly (Figs. 21, 22). Aecidia reached 

 maturity September 10. Fig. 43 shows an optical section of a 

 peridial cell from the central part of an aecidium. The entire 

 surface is smooth. The walls are not always of uniform thickness 

 and the lumen does not appear to extend the full length of the 

 cell. It is difficult to obtain such a view of an outer or inner 

 surface of the cells of the peridia on Aronia. Those on the 

 Amelanchier do not coil up in water to any great extent and, as 

 they are merely "wavy" in outline, views of all sides may be 

 obtained. Cultures made later show that two or three tubercular 

 galls occasionally coalesce (Fig. 21) forming a solid mass of tissue 

 from which the same number of aecidia develop. The basal gall 

 subiculum on Aronia is often conspicuous from the first (Fig. 4). 

 The horn-like parts are secondary. This is also in a measure true 

 for the fungus on Amelanchier, where there is a very slight primary 

 swelling, and one can not tell at first just how many ovoid out- 

 growths, and therefore how many aecidia, will be formed at any 

 particular point of infection. 



It is unnecessary to describe this rust as it appears on Amelan- 

 chier further at this point than to say that in the characters of 

 the peridial cells and in the manner of dehiscence it corresponds 

 very well in general with exsiccati specimens of Roestelia Botry- 

 apites on Amelanchier or to the original description of R. Ellisii, 

 which has long been considered a synonym of R. Botryapiies. 

 In spite of the fact that no Gymnosporangium biseptatum was kept 

 in the greenhouse the possibilities of ( 



