7 o RESEARCHES ON FUNGI 



substances are excreted, one by one hypha and the other by the other 

 hypha, leads us into difficulties when we try to account for the fact 

 that, in a single mycelium, any hypha will fuse with any other hypha 

 that is near enough to it and that, in a single species, any mycelium 

 produced from a spore, a conidium, or an oidium will fuse with any 

 other mycelium. Let us consider how our theory of two chemical 

 substances for each vegetative hypha- to -hypha fusion becomes 

 complicated when we have to explain the formation of fusions 

 between any two mycelia of a single species. 



Let A, B, C, D, designate a series of mycelia all belong- 

 ing to a single fungus species and all sexually similar, and let us 

 suppose that, in any combination of two of these mycelia, there is 

 formed a single hypha-to-hypha fusion. When A fuses with B, on 

 our theory, two substances are excreted. Let a be the substance 

 excreted by A and b the substance excreted by B. Then a and 6 

 are different substances. When A fuses with C, the substance 

 excreted by C must be different from that excreted by A. Let c be 

 the substance excreted by C. When B fuses with C, the substance 

 excreted by B must be different from that excreted by C, i.e. the 

 substances b and c are different from one another. So far, we have 

 been obliged to assume the existence of three distinct chemotropic 

 substances a, b, and c excreted by A, B, and C respectively. With 



every additional mycelium, D, E, F, that we take into 



consideration we must assume the existence of a new chemical 



excretion, d, e, f, to account for the phenomena observed. 



Thus, if we have interfusions between any two of ten thousand 

 mycelia, we are forced to assume the existence of ten thousand 

 different chemical excretions to account for the tropic phenomena 

 observable. Thus in developing the theory that two different 

 chemical substances are excreted in each hypha-to-hypha fusion 

 between any two like mycelia of one and the same species we are 

 faced with a reductio ad absurdum. We cannot accept the view 

 that, in any fungus species, every mycelium is able to produce an 

 excretion different from that of every other mycelium and that the 

 number of such excretions is indefinitely great. 



How then shall we account for the fact that between any two 

 like mycelia of one and the same species, hyphal fusions are readily 



