CHAPTER III. 

 EELATION OF PARASITE TO SUBSTRATUM. 



§ 9. EFFECT OF THE SUBSTRATUM ON THE DEVELOPMENT 

 OF THE PARASITE. 



A NUMBEK of parasitic fungi live only on one species of 

 host. For example Sderotinia baccarum on Vaccinium Myrtillus, 

 Chrysomysca abietis on. Picea eoccelsa, Tnphragmium tdmariae on 

 Spiraea ul/maria, Hysterium nervisequiuvi on Abies pedinata, 

 RhytismM androrrudae 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 Rhytisma salicimim 

 found on all species of willow, and Rhytisma acerinum 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, Phytophthora omnivora 

 on many different plants, Phyllaetinia siiffulta on leaves of 

 Coryliis, Pagus, and many other trees ; Glaviceps purpurea on a 

 large number of cereals and grasses, Cystopus candidus on many 

 Cruciferae, and Nectria cinnaharina 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 Zeitung, 1867, p. 264. 



