﻿Dodge: Effect of host on Gymnosporangium 527 



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June 3 



IE! 



June 21 § 

 June 23 



June IS 



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365 \Aronia arbutifolia . . . 



366 lAronia arbutifolia . . . 

 368 Uronia arbutifolia... 

 372 lAronia atropurpurea . 



375 i/rZan/gra"'.""': 



July 

 June 



July 



2 ; July 18 



July 18 July 23 

 Aug. ? Aug. 10 



appear (Fig. io), but the majority are not materially altered 

 in shape (Fig. 12). Fig. 9 shows how the fungus may also attack 

 young twigs below the growing point. A large number of aecidia 

 develop on such malformations and on the fruit when it is attacked. 



The aecidia are about one half millimeter in diameter and two 

 to five millimeters in height, tapering gradually to a fine point 

 (Fig. 15). Frequently those on Aronia nigra (Fig. 18) are taller. 

 The dehiscence of the peridium is shown in Figs. 15, 16, and 17. 

 The cells at the apex do not split apart, and, as a result of the 

 laceration of the portion of the peridium below the apex (Fig. 16) 

 and the reaction of the mature cells to atmospheric changes, the 

 top breaks away (FiG. 19), leaving the lower part of the cup fringed 

 with a tangle of cells. The inner surface of a peridial cell is 

 coarsely warted and most of them are pointed. Some have a 

 notch at one end (Fig. 41), showing that they may overlap or 

 dovetail. The only species known to possess such peridial cells 

 is Roestelia transformans, the species that produces hypertrophies 

 on Aronia such as I have described. The peridium is said (9, 16) 

 to dehisce at the apex first and gradually fall away. It is likely 

 that collectors have failed to note the manner in which the tip end 

 disappears. The galls are green until long after the aecidia are 

 mature and not brownish as one finds them in dried specimens. 



The twigs of Amelanchier intermedia used in number 203a 

 were obtained at Newfield April 19 and inoculated April 25 with 

 sporidia taken from swollen sori of G. fraternum. Spermogonia 

 appeared on several leaves May 6. A potted root sprout of A. 

 intermedia also from Newfield was used for number 249. At the 



