464 RESEARCHES ON FUNGI 



Stropharia e^imyces.Stropharia epimyces is a North American 

 parasite which confines its attack to the frnit-bodies of two of the 

 largest Coprini, namely, C. comatus and C. atram.entarius . For 

 illustrations of S. epimyces on Cojjrinus comatus and for a discussion 

 of its parasitism the reader is referred to Chapter VII (Figs. 65 

 and 66, pp. 165 and 167). Here I shall simply add a few remarks 

 of a comparative nature. 



Stropharia epimyces appears to be the only agaric parasitic on 

 other agarics which always completely masters its host. The 

 Coprinus fruit-bodies attacked lose their characteristic shape, 

 become dwarfed, are rendered more or less sterile, and never expand, 

 while their nutrient substances are exhausted by the parasite to form 

 fruit-bodies of its own. As a rule the other agarics parasitic on 

 agarics — Boletus parasiticus, Leptonia parasitica, Claudopus siih- 

 depluens, Volvaria Loveiana, Nyctalis asterophora, and N. parasitica 



deform their hosts either but slightly or not at all and doubtless 



allow them to produce at least some spores from the hymenium, 

 whether this be situated within their gleba (Scleroderma), on the 

 inner surface of their hy menial tubes {Poly poms perennis), or upon 

 the exterior of their gills {Cantharellus cibarius, Clitocybe nebularis, 

 Russulae, and Lactarius vellereus). In completely mastering its 

 host, Stropharia ejnmyces exhibits a high specialisation which is 

 analogous with that of Hyjiomyces lactifiuorum ^ on Lactarius 

 piperatus and of Ustilago tritici on wheat. 



It may be asked : why does Stropharia epimyces attack only 

 certain Coprini ; Volvaria Loveiana only certain species of Clitocybe ; 

 and the parasitic species of Nyctalis only certain Russulae, Lactarii, 

 etc. ? The answer to this question, if we knew it, would probably 

 be in chemical terms. Doubtless, where a parasite is specialised 

 to attack a single host or a few related hosts, the chemical juices of 

 the host or hosts must afford a very perfect nutrient medium to the 

 hyphae of the parasite and be without any toxic or other detrimental 

 effects upon them — a combination which may be rare. Also for 

 successful parasitism the juices of the host must either act upon the 

 hyphae of the parasite in a positively chemotropic maimer, or at 

 least be of such a nature as to permit the hyphae of the parasite to 

 1 CJ. these Researches, vol. ii, 1922, pp. 58-69. 



