26 RESEARCHES ON FUNGI 



The principle involved in the mode of observation was that of 

 continuous watching of a particular part of a living mycelium with 

 a view to witnessing all those stages in growth leading up to, and 

 culminating in, the actual union of two hyphae of one and the same 

 mycelium. 



A younger hypha growing toward the side of an older hypha 

 may either pass the older hypha or fuse with a process which this 

 sends out. Two branch-hyphae whose ends are growing toward 

 one another may pass one arfbther or fuse with one another. Passing 

 is the rule in younger rapidly growing mycelia. Also hyphae or 

 hyphal processes upon which one may fix one's attention as likely to 

 take part in a hyphal fusion may cease to grow. Hence one's 

 observations often yield negative results with consequent loss of 

 time. In any one mycelial preparation it was not found possible to 

 observe more than one or two fusions in a day. 



A Generalisation on Hyphal Fusions. — As a result of comparative 

 observations made on the species of Ascomycetes and Basidiomycetes 

 listed in the previous Section, I have come to the important general 

 conclusion that, in the mycelium of the Higher Fungi, all hyphal 

 fusions are essentially end-to-end ones, i.e. that, when a fusion takes 

 place, it takes place between the end of one hypha and the end 

 of another hypha. The youngest parts of hyphae — the growing 

 points — are alone involved in the final stages of the fusion process. 

 The evidence upon which this conclusion is based will apear in what 

 follows. 



It was formerly held by myself. Mile Bensaude, and others that 

 hyphal fusions are often end-to-side ones, i.e. that often the end of 

 a younger hypha fuses directly with the side of an older hypha. 

 However, direct observations on the formation of hyphal fusions in 

 living mycelia do not support the view that end-to-side fusions take 

 place. A further discussion of this matter will be deferred until the 

 facts yielded by my new investigations have been recorded. 



The Four Kinds of Hyphal Fusions. — Granted that end-to-end 

 fusions include all those occurring in mycelia. the various types of 

 hyphal fusions may be classified as follows: (1) hypha-to-hyj)ha 

 fusions ; (2) hypha-to-peg fusions, (3) peg-to-peg fusions, and (4) 

 hook-to-peg or clamp-connexion fusions. In this terminology : by 



