REED: SPECIALIZATION OF PARASITIC FUNGI 391 



has succeeded in producing aecidia on twenty-two species, belonging 

 to fifteen genera, distributed among six different families, as follows: 



1. Polygonaceae : Polygonum aviciilare, P. erectiim and P. ramosissi- 



mum. 



2. Chenopodiaceae : Salsola pestijer, Chenopodium album, C. glaucum, 



C. lanceolatum, C. pagoniim, Monolepis nuttalliana and Kochia 

 scoparia. 



3. Amaranthaceae : Amaranthus retroflexiis and A. blitoides. 



4. Nyctaginaceae : Abronia fragrans. 



5. Cruciferae: Capsella Bursa-pastoris, Lcpidium densiflorum, L. 



medium, Erysimum asperum, Sophia pinnata, Roripa palustris, 

 Thaspi arvense and Sisymbrium altissimum. 



6. Capparidaceae : Cleome serrulata. 



It is also suggested that species of Papaveraceae may be aecidial 

 hosts for the same rust. 



Bock (19) has carried out rather extensive cultural tests with 

 Puccinia Gentianae (Str.) Link. He reports no evidence for host 

 specialization, finding that a large number of species of Gentiana were 

 readily infected with rust from two different species. 



Another illustration of the same condition is reported by Camilla 

 Popta (109) who has been able to infect a number of umbellifers with 

 the same race of Protomyces macrosporus. The following plants were 

 infected with the fungus from Aegopodium podograria: Cicuta virosa, 

 Seseli montanum, Libanotis vulgaris, Palimba chalraii, Bubon gemmif- 

 erum, Pachypleurum alpinum, Bunium virescens, Ferula thyrsi flora, 

 Trinia vulgaris and Athamanta cretensis. 



If now we compare the degree of specialization found in the 

 different parasitic fungi we find the greatest divergences. In a general 

 way the specialized races may be grouped on the basis of their host 

 range as follows : 



1. Specialized races restricted to certain species of a genus of 

 hosts. Here belong the specialized races of Erysiphe graminis within 

 the genera Bromus and Hordeum; of Puccinia dispersa within the 

 genus Bromus; the specialized races of Phragmidium disciflorum, 

 Puccinia Centaureae, P. Epilobii-tetragoni, P. Helianthi, P. Hieracii, 

 P. Pulsatillae, P. Ribis, P. Ribesii-Caricis, P. Caricis-montanae, 

 Uromyces Poae, U. proeminens and Melampsora Euphorbiae. 



2. Specialized races restricted to a particular genus of host plants. 

 A number of specialized races of this sort are known. Among the 

 Erysiphaceiie we find the specialized races of Erysiphe graminis on 

 Agropyron, Dactylis, Poa and Secale and of Erysiphe cichoracearum 

 on Aster and Solidago. Among the rusts we find the races of Puccinia 

 graminis on Aira, Poa, Calamagrostis and Apera; of P. coronata on 



