THE FUNCTIONS OF HYPHAL FUSIONS 183 



sex mate with each other, as may be seen in plate cultures, they 

 unite with each other at a number of points, so that doubtless the 

 exchange of nuclei takes place across many bridges. The formation 

 of numerous hyphal fusions between mating mycelia therefore 

 assists the beginning of the sexual process. 



(3) Passage of nuclei through a haploid mycelium becoming 

 diploidised. As will be shown in the next chapter, in Coprinus 

 lagopus, when a large haploid mycelium of one sex is being diploidised 

 by nuclei derived from an inoculum consisting of a tiny haploid 

 mycelium of opposite sex, the nuclei move through the large 

 mycelium in all directions and the movement ends by the estabhsh- 

 ment of pairs of conjugate nuclei (indicated by clamp-connexions) 

 in all the leading hyphae of the large haploid mycelium. The rapid 

 diploidisation of the large haploid mycelium by means of nuclei 

 derived from the tiny inoculum would be impossible were it not 

 for the fact that the large haploid mycelium is a finely-meshed 

 three-dimensional network of hyphae. The nuclei do not need to 

 go to the centre of the mycelium and then radially outwards to all 

 the thousands of branches ; but, owing to the netted condition of 

 the mycelium (c/. Fig. 88, p. 158), they can pass around the mycehum 

 tangentially, using numerous lateral hyphae as channels. That 

 they do use such channels has been proved {vide infra) by excising 

 the central part of a large haploid mycelium, applying to the peri- 

 phery of the mycelium remaining a tiny haploid mycelium of 

 opposite sex, and then observing that the large haploid mycehum 

 soon becomes everywhere diploidised all around its periphery. 

 There can be no doubt that the netted condition of a haploid 

 mycelium of Coprinus lagopus, and doubtless of other heterothalhc 

 Hymenomycetes, is of very great importance for the diploidisation 

 process. 



(4) Mechanical injury. Vegetative mycelia, like the vegetative 

 parts of all other plants, are Uable to injury from various mechanical 

 causes. If a large vegetative mycehum were not a network, any 

 break in one of its thin hyphae would divide it into two parts ; 

 but, since it is a network, the breaking of some of its hyphae may 

 still leave it as a unit and capable of acting as such in the formation 

 of a fruit-body. Furthermore, there is always the possibility of 



