﻿Dodge: Effect of host on Gymnosporangium 537 



The galls of '' Gymnosporangium fraternum on Amelanchier" 

 are at first small wart-like growths, somewhat flattened or de- 

 pressed at the center (Fig. 20). Ten or twelve weeks after inocula- 

 tion the pit disappears and the gall begins to elongate, becoming 

 ovoid (Fig. 21). The apex is marked by several rounded promi- 

 nences (Fig. 25). There are no such fluted collars visible on the 

 galls on Aronia. Thaxter (20) and Arthur (2) report that it re- 

 quires from four to five months for the complete development of 

 Roestelia Botryapites on Amelanchier. My records show that it 

 takes about the same time for Gymnosporangium fraternum on 

 Amelanchier, while on Aronia the aecidia mature six or eight weeks 

 after inoculation. 



Of the galls produced on Amelanchier when infected with G, 

 hiseptatum Farlow (4) says: "Although the peridia are not yet 

 ripe there can be no doubt that the species is R. botryapites, as 

 the tubercular swellings produced can not be mistaken for those 

 of any other species known in this country." 



I have shown that G. fraternum produces an aecidial form on 

 the Amelanchier, which resembles very closely the aecidium 

 known as Roestelia Botryapites, proved to be connected with G. 

 hiseptatum. It would be of no consequence whatever to draw 

 conclusions as to the relationship of these two Gymnosporangia, 

 based on even the most critical examination of the existing 

 exsiccati of R. Botryapites which have all been collected in the 

 field. There could be no assurance that two collections bearing 

 the same number had the same origin. The spots on two leaves 

 in the same package or even two spots on one leaf may have 

 originated from two different teleutospore forms, one from the 

 caulicolous, the other from the foliicolous form. This question 

 can be attacked to greater advantage when a more extended 

 opportunity has been afi^orded for a comparison of the various 

 stages in their development, side by side on the same plant, of 

 these two aecidia grown under controlled conditions. There are, 

 however, certain hypotheses that may well be stated here with 

 considerations pro and con. 



It is possible that G. fraternum and G. hiseptatum are two dis- 

 tinct species, as it happens, having on Amelanchier aecidia much 

 alike. The following points support such a view : (i) the absence 



