SIGNIFICANCE OF ACTION OF DIPLOIDS 265 



and a diploid mycelium, the diploid mycelium diploidises the 

 haploid, has an important bearing on the course of the life-history 

 of Coprinus lagopus as the fungus grows under natural conditions. 



Coprinus lagopus is coprophilous, and its relations with its environ- 

 ment may be thus briefly summarised : the fruit-bodies appear on 

 horse dung in fields and pastures ; the spores liberated from the pilei 

 in great numbers are carried off by the wind and are deposited on 

 herbage ; grazing horses eat the herbage with the spores attached 

 thereto ; the spores pass down the alimentary canal of the horses 

 concerned unharmed, and so are deposited in the solid faeces where 

 they germinate and produce a mycelium which, in the course of 

 8-15 days, may give rise to new fruit-bodies. 



The number of spores of Coprinus lagojjus which come to be 

 embedded in a single horse-dung ball deposited in a pasture must 

 be very variable ; but, doubtless, it is often very great, amounting 

 to more than one hundred or even one thousand. When many 

 spores of our fungus are embedded in a single ball, the haploid 

 mycelia produced by them must of necessity come into contact 

 with one another as they develop. Since it has been shown (p. 245) 

 that any two mycelia of Coprmus lagopus can form hyphal fusions 

 with one another, we are justified in supposing that, when a dung- 

 ball contains many spores, the monosporous mycelia which the 

 spores produce must, on coming into contact with one another, 

 unite to form a single compound mycelium. 



The mycehum of Coprinus lagopus in a dung-ball produces 

 fruit-body rudiments and fruit-bodies only at the exterior surface 

 of the dung-ball, and never in the dung-ball's interior. 



Coprinus lagopus is able to produce haploid fruit-bodies on a 

 haploid mycelium and diploid fruit-bodies on a diploid mycelium. 



A haploid fruit-body of Coprinus lagopus : ( 1 ) develops rela- 

 tively late on its mycelium ; (2) its pileus is pale owing to the 

 development of but few or no spores on its gills ; (3) its pileus often 

 fails to expand properly ; (4) it liberates but few or no spores ; 

 and (5) its spores, when produced, are all of one sex and of the same 

 sex as that of the parent mycehum, i.e. {AB) or {ab) or (^6) or {aB). 



A diploid fruit-body of Coprinus lagopus, on the other hand : 

 (1) develops relatively early on its mycelium ; (2) its pileus turns 



