(4°4) 



alternating between two sets of hosts can be taken as a measure 

 of the "affinity" or "relationship" existing between them, and yet 

 the results of this compilation are not without interest and perhaps 

 significance. In considering table III it must be borne in mind 

 that oftentimes several genera serve as aecial hosts for a species, 

 which with a single exception (G. germinale) is limited to one genus, 

 or section, for its telial hosts. Crataegus and Amelanchier ; serv- 

 ing as the hosts for 1 1 and 12 species, respectively, are very much in 

 the lead of the other aecial hosts. As the conditions are now known 

 from cultures, Amelanchier seems to be of a more generalized type, 

 serving as host for species coming from 4 of the 5 sets of telial hosts 

 while no other aecial host serves for more than 3 of the telial 

 host-groups. 



Factors Affecting the Distribution of Gymnosporangium 

 The data concerning the relation of the distribution of the fungi 

 to the area over which they might be distributed, so far as host 

 conditions are concerned, may be expressed thus: 

 A. Species of Gymnosporangh 



or practically coexte: 



sets of hosts— 



a. Distribution practically coextensive with area common 



to both sets of hosts — 

 (1) G. Juniperi-virginianae, (2) G. globosum, (3) G. Nidus- 

 avis, (4) G. Nelsoni, (5) G. Davisii, (6) G. inconspicuum, 

 (7) G. Blasdaleanum, (8) G. Botryapites. 



b. Distribution in central part of area common to both sets 



of hosts— 

 (1) G. trachysorum, (2) G. exterum, (3) G. Betheli, (4) G. 



(1) G. clavariaeforme, (2) G. cornutum, (3) G. juniperinum, 

 (4) G. germinale, (5) G. corniculans, (6) G. exiguum. 

 From the foregoing data it becomes evident that the tendency 

 s toward the distribution of the fungi over the entire geographic 



