i82 RESEARCHES ON FUNGI 



which is being diploidised by numerous and varied routes ; (4) they 

 convert all mycelia, whether haploid or diploid, into a network of 

 such a kind that a myceUum, when injured by the breaking of some 

 of its hyphae, still remains a unit and can act as such in the pro- 

 duction of a fruit-body ; and, finally, (5) in any single species, 

 whether homothalUc or heterothalKc, they permit of any number 

 of adjacent myceUa, whatever may be their sexual state, uniting 

 to form a compound myceUum and thus acting as a social unit in 

 the production of fruit-bodies and spores. A brief discussion of the 

 five functional advantages accruing to hymenomycetous mycelia 

 as a result of the formation of hyphal fusions will now be attempted. 



(1) Conduction oj food materials. A fruit-body of Coprinus 

 sterquilinus or any other Hymenomycete, or a sclerotium of Coprinus 

 stercorarius, etc., is produced entirely at the expense of the vege- 

 tative myceUum, and all the food materials required for its develop- 

 ment pass along myceUal hyphae to it. The exact place on a 

 mycehum where a fruit-body or a sclerotium is to develop to 

 maturity is decided by external conditions. It is important, there- 

 fore, that, when a fruit-body or a sclerotium begins its development, 

 wherever it may be situated it shall be able to receive the contents 

 of the vegetative myceUum without difficulty. A large vegetative 

 myceUum without any hyphal fusions and entirely un-netted 

 would be about as unfitted for conducting food materials to a large 

 fruit-body as a single un-netted railway system would be for carrying 

 goods and passengers in a country such as England. A finely- 

 netted mycelium provides many different channels through which 

 food materials can be conducted to a developing fruit-body or 

 sclerotium and therein lies a very important part of its physiological 

 significance. 



(2) Mating of mycelia. In a heterothallic species, e.g. Coprinus 

 lagopus, it is obvious that, if two haploid myceUa are to interact 

 sexually, somehow or other they must unite. The union is actually 

 accompUshed by one or more hyphal fusions. Theoretically, a 

 single hyphal fusion between two haploid myceUa which are able 

 to mate with each other might be sufficient to allow of an inter- 

 change of nuclei which would initiate the diploidisation process in 

 the two myceUa ; but, actually, when two myceUa of opposite 



