THE FORMATION OF HYPHAL FUSIONS 71 



produced ? It seems to me probable that, in a single species, all 

 the vegetative fusions, whether taking place between two hyphae 

 of a single mycelium or between a hypha of one mycelium and a 

 hypha of another mycelium, are alike, i.e. that the chemical ex- 

 cretions taking part in the telemorphic and zygotropic phenomena 

 of one hyphal fusion are identical in composition with those taking 

 part in the similar phenomena in any other hyphal fusion. Granted 

 that all the hypha-to-hypha fusions in any species of the Higher 

 Fungi are due to a single pair of chemical substances excreted by 

 the ends of the two hyphae concerned in each fusion, we are still 

 confronted with theoretical difficulties ; for one may ask : in any 

 hypha-to-hypha fusion, what causes one hypha to produce one 

 of the two substances and the other hypha the other of the 

 two substances ? To this question I can give no satisfactory 

 answer. 



Sufficient has been said to indicate the difficulty of accounting 

 for the telemorphic and zygotropic reactions which take place 

 in vegetative hyphal fusions on the basis of chemical excretions. 

 So far as vegetative fusions are concerned, we have as yet no 

 experimental evidence that the hyphae excrete any chemotropic 

 substances whatever. It is possible that the stimuli which cause 

 the two hyphae entering into a hypha-to-hypha fusion to become, 

 as it were, polarised in respect to one another, may be non-chemical. 

 If they are purely chemical, it remains for this to be demonstrated 

 by exact experiment. 



Recently and since the above was written, Vandendries and 

 Brodie * have announced the results of some remarkable experi- 

 ments which they have made on the cause of the mutual repulsion 

 which takes place between certain haploid mycelia, between (Ab) 

 and {AB) or between (ab) and (aB), of Lenzites betulina. The 

 repulsion is more marked in aerial hyphae than in hyphae embedded 

 in the substratum, and can be observed when the hyphae are 

 separated from one another by a distance of 3*5 mm. The intro- 

 duction of a north or south pole of a magnet between the mycelia 



1 R. Vandendries and H. J. Brodie, " La Tetrapolarite et l'Etude experimental 

 des Barrages sexuels chez les Basidiomycetes " (Note prelim inaire), Bull, de VAcad. 

 roy. de Belgique, classe de Sci., ser. 5, T. XIX, 1933, pp. 3-8. 



