THE FORMATION OF HYPHAL FUSIONS 3 



It is important to distinguish between (1) a hyphal contact, 

 (2) a hyphal adhesion, and (3) a hyphal fusion or hyphal anastomosis. 

 A hyphal contact may be said to exist where two hyphae come into 

 contact with one another but do not adhere to one another, so that 

 they can be readily separated. In a hyphal adhesion two hyphae 

 come into contact with one another, end-to-end, end-to-side, or 

 side-to-side, and adhere to one another without fusing ; while, in 

 a hyphal fusion, two hyphae come into contact end-to-end, adhere 

 to and flatten out against one another, and then the double 

 partition-wall breaks down and disappears, so that the two masses 

 of protoplasm become confluent. 



Fusions or anastomoses may be divided into (1) vegetative and 

 (2) sexual. Vegetative fusions are those fusions which promote 

 vegetative processes, such as the conduction of food materials, the 

 conveyance of stimuli, etc., while sexual fusions are those which 

 assist the coming together of nuclei destined to co-operate in a 

 sexual process. Typical vegetative fusions are those which occur 

 between ordinary hyphae in most mycelia, while typical sexual 

 fusions are those which take place between two morphologically 

 distinguishable sexual organs, e.g. the antheridium and the 

 trichogyne of the oogonium in Pyronema confluens. 



In the Hymenomycetes, e.g. Coprinus lagopus, when two com- 

 plementary haploid mycelia, such as (AB) and (ab), are mated on 

 a dung-agar plate, many hyphal fusions take place between the two 

 mycelia. Doubtless some of the passage-ways thus formed are 

 used- for the exchange of nuclei during the initiation of the 

 diploidisation process, while others are not. In this case it is a 

 matter of chance which of the fusions are strictly vegetative and 

 which assist the sexual process, and the attempt to distinguish 

 sharply between vegetative and sexual fusions here breaks 

 down. 



In the Mucorineae, the parasitic species attack their relatives in 

 various ways. Thus Syncephalis nodosa bores into and produces 

 a mycelium within the sporangiophores of Pilobolus longipes ; 

 Piptocephalis Freseniana attacks the hyphae of Mucor Mucedo by 

 means of fine haustoria sent out in groups from appressoria ; while 

 Parasitella simplex and Chaetocladium Brefeldii form hyphal fusions 



