312 RESEARCHES ON FUNGI 



were relatively longer and which tapered toward the base (best 

 seen in Fig. 136 where the white fibrillae have been removed), and 

 in (2) having narrower gills and, relatively, a more pointed and 

 narrower pileus (Figs. 135, 136, and 138, O, P). When one com- 

 pares fruit-bodies grown in the light (Figs. 133, 134, 138, E-N) 

 with fruit-bodies grown in complete darkness (Figs. 135, 136, and 

 138, 0, P), it at once becomes evident that the form of the fruit- 

 body of C. lagojms is moulded to some extent at least by the mor- 

 phogenic stimulus of light. Here, as in C. macrorhizus,^ light inhibits 

 the development of the tapering pseudorhizal stipe-base, so that 

 this only appears in fruit-bodies which have grown up in the dark. 



(4) Sterile fruit-bodies. Sterile fruit-bodies of Coyrinus lagopus, 

 although but rarely or never seen under natural conditions, fre- 

 quently occur in pure cultures of the type represented in Fig. 132 

 (p. 304). In Fig. 137 (p. 313), two sterile fruit-bodies are shown 

 on the left and a fertile fruit-body of about equal size on the right. 

 The sterile fruit-bodies are easily distinguished by their pale 

 whitish-yellow colour and by the non-development of the spores, 

 whereas the fertile fruit-body is blackish owing to the spores 

 which are present in vast numbers on the gills. A similar com- 

 parison for some older fruit-bodies with expanding pilei is made 

 possible in Volume II by means of Figs. 20 and 21 (pp. 71 and 72). 

 In Volume II an illustration of the structure of a sterile gill is also 

 provided (Fig. 22, p. 73). 



There are degrees of sterility. Moreover, completely or partially 

 sterile fruit-bodies may develop either in the light (Fig. 137) or in 

 the dark (two pilei in centre of Fig. 136, p. 311). 



Coprinus lagopus is heterothallic. Miss Mounce,^ working in my 

 laboratory with pure cultures, observed that the fruit-bodies arising 

 from a secondary (diploid) mycelium produced by the union of two 

 primary (haploid) mycelia of opposite sex are, as a rule, perfectly 

 fertile and appear soon after the mating of the two primary mycelia 

 has been effected, whereas the fruit-bodies arising from unmated 

 primary (haploid) mycelia are sterile and develop tardily. This 

 general association of fertility with the diploid condition of the 

 mycelium and of sterility with the haploid condition, observed by 



1 Vide infra, vol. iv. ^ These Researches, vol. ii, 1922, pp. 73-74. 



