

Aecia. Hosts 





Total 



North 









Order 



Family 



Genus 



Species 



Amenca 













Crataegus 



„ 



in 





_ 



_ 























Pyrus 





























Rosales 



Malaceae 

 (Pomaceae) 



Sorbus 



Cydonia 

 Cotoneaster 



Per^phyllum 



6 

 5 



J 



: 



I 



: 



Resales 



Rosaceae 















Rosales 



Hydrangi- 



Philadelphia 

 Fendlera 



\ 



j 



: 



: 



; 



Pinales 



JU a n cea £ e" 



^fsa'Hna 



1 



1 



_ 



_ 



- 



The s 



i of a 



:ial ho; 



- lead 1 



considei 



[on of 



i sugges 



table II. Crataegus and Avielanchier are seen to serve as hosts 

 for many more species in North America than in Europe. This, 

 it would seem, must bear some relation to the greater complexity 

 and the more general distribution of these genera in North America. 

 With regard to Pyrus the situation is entirely different, there being 

 a total of 7 species known on this host almost equally divided between 

 North America, Europe, and Asia. Certain other apparent discrep- 

 ancies are at once understood when the distribution of the hosts is 

 considered. Aronia and Peraphyllum serving as hosts only in 

 North America are exclusively American genera; Cotoneaster and 

 Mespilus, two hosts which are not recorded for North America, are 

 not American genera; and Pourthiaea, recorded only for Asia is 

 a strictly Asiatic genus. 



Re: 



Anti 





■ He: 



By a comparative study of the various species of Gymnosporan- 

 gium an attempt has been made to discover something which might 

 give a clue to an explanation why the families Juniperaceae and 

 Malaceae are so universally and almost exclusively utilized as hosts. 

 Although the efforts have not been productive of any positive 

 results, certain data seem worthy of presentation. It is a notable 



