268 RESEARCHES ON FUNGI 



from its diploid mycelia being able to diploidise appropriate haploid 

 mycelia, let us consider a ease which, although extreme, brings out 

 the point at issue. Let us suppose : (1) that, in a newly-dropped 

 dung-ball, there are scattered fairly uniformly in a plane down the 

 centre fifty spores of which the middle spore has the constitution 

 (AB) and all the other spores the constitution (ab) ; (2) that all 

 the spores germinate and produce mycelia which eventually make 

 contacts with their nearest neighbours ; and (3) that the haploid 

 myceUum {AB) meets and pairs with a haploid mycelium {ab) with 

 resultant mutual diploidisation and the formation of a diploid 

 myceUum {AB)^{ab) before this diploid mycelium comes into 

 contact with any other mycelia. We know, on the basis of exact 

 experiment, that the diploid mycelium {AB)-\-{ab) on coming into 

 contact with the other forty-eight haploid mycelia {ab) separately 

 or as a net-work would diploidise them, and so cause diploid 

 myceUum to be developed all around the outside of the dung-ball. 

 Such a diploidisation of all the remaining forty-eight myceHa {ab) 

 by the diploid mycelium {AB)-\-{ab) would lead to the production 

 of diploid instead of haploid fruit-bodies at the surface of the 

 dung-ball, and so would facilitate the production of spores and 

 therefore also the dissemination of the species. On the other hand, 

 if the diploid mycelium {AB)-{-{ab) were unable to diploidise the 

 remaining forty-eight haploid myceUa, then, since the diploid 

 mycelium {AB)-\-{ab) had its origin at the centre of the dung-ball, 

 most, and possibly all, of the network of myceUum developed at and 

 near the surface of the dung-ball would be haploid, and this exten- 

 sive haploid mycelium would give rise to nothing but imperfect 

 and unprofitable haploid fruit-bodies. Thus, in the case under 

 discussion and doubtless also extremely often under natural con- 

 ditions, it is certain that the diploidisation of a haploid myceUum 

 by an appropriate diploid myceUum is an advantageous pheno- 

 menon, in that it increases the number of spores which the fruit- 

 bodies produce and so assists in maintaining the species in the 

 environment in which it is fitted to live. 



The Biological Significance of Conjugate Nuclei. — Let n repre- 

 sent the number of chromosomes in any nucleus and a pair of 

 brackets ( ) a nuclear membrane. Then a pair of conjugate nuclei 



