VARIOUS OBSERVATIONS 



73 



when they should proceed to the construction of the spores, it is 

 not surprising that the cystidia do not differ in appearance from 

 those which are present in fertile fruit-bodies. 



The cause of the arrested hymenial development for the present 

 is a mystery. It cannot be the action of a parasite, because sterile 

 fruit-bodies make their appearance in pure cultures ; and it cannot 

 be a deficiency of food material in the substratum, for sterile fruit- 

 bodies come up in pure cultures on fresh sterilised horse dung. 



FIG. 22. The histology of a gill of a sterile fruit-body of Coprinus lagopus (= (7. 

 fimetarius). A, optical section through the hymenium parallel to its surface ; 

 b, a basidium ; p, a paraphysis. B, cross-section through part of a gill : the 

 hymenium contains long basidia, Ib ; short basidia, sb ; and paraphyses, p. 

 C, a cross-section through the hymenium of two adjacent gills before the 

 expansion of the pileus : a cystidium, c, of normal size is stretched across an 

 interlamellar space, i ; Ib, a long basidium ; sb, a short basidium ; p, a para- 

 physis. Magnification, 293. 



Coprinus lagopus is heterothallic. In her plate cultures of this 

 fungus Miss Mounce, working in my laboratory, observed that the 

 fruit-bodies arising from a secondary (diploid) mycelium produced 

 by the union of two primary mycelia of opposite sex were perfectly 

 fertile and appeared soon after the mating of the two primary 

 mycelia had been effected, whereas the fruit-bodies arising from 

 unmated primary (haploid) mycelia were sterile and developed 

 tardily. 1 Here, therefore, fertility was associated with the diploid 

 condition of the mycelium and sterility with the haploid. 



A great many spores of Coprinus lagopus were sown together on 



Vide infra, vol. iv, Chap. III. 



