CHAPTER III. 

 RELATION OF PARASITE TO SUBSTRATUM. 



§ 9. EFFECT OF THE SUBSTRATUM ON THE DEVELOPMENT 

 OF THE PARASITE. 



A NUMBER of parasitic fungi live only on one species of 

 host. For example Sderotmia haccarum on Vaccinium Myrtilhi.a, 

 ChrysomyoM abietis on Ficea excelsa, Triphragmium ulmariae on 

 Spiraea ulmaria, Hysterium nervisequium on Abies pectinata, 

 Rhyiisma andromf.dae on Andromeda polifolia. De Bary^ proposed 

 for cases like this the term monoxeny, while to cases in which a 

 parasite frequents several different species of host he gave the 

 name polyxeny, or more particularly, dixeny, trixeny, etc. As 

 examples of polyxeny may be mentioned lihytisma salicinvmi 

 found on all species of willow, and Bhytisma acerinvm on the 

 genus Acer. Other parasites attack not only different species 

 of some genus, but also different genera ; thus, Puccinia graminis 

 occurs on various cereals and grasses, Pliytoplitliora omninora 

 on many different plants, FhyUactinia suffulta on leaves of 

 Corylus, Fag us, and many other trees ; Clavicejps piirpurea on a 

 large number of cereals and grasses, Cystopus candidus on many 

 Cruciferae, and Neetria cinncdwrina on all kinds of broad-leaved 

 trees. 



Monoxeny and polyxeny must be carefully distinguished from 

 the autoecism and heteroecism of the Uredineae. Many species 

 of this group go through their whole life-history, and produce 

 all their forms of spore on the same host, others, however, pro- 

 duce some forms of spore — spermatia and aecidiospores — on one 

 host, and the remainder — uredospores and teleutospores — on 

 ^ Botanische ZtUuiui, 1867, p. 264. 



