396 RESEARCHES ON FUNGI 



clamp-connections are a sign that the nuclei in the hyphae are 

 paired. Max Hirmer l has observed that the cells of the stipe 

 and pileus-flesh of Psalliota campestris contain not pairs of nuclei, 

 but groups of individual nuclei numbering up to eleven in each 

 group. The absence of clamp-connections in the mycelium of a 

 Mushroom bed is therefore probably due to the fact that the nuclei 

 are not paired but exist in little groups. In many Hymenomycetes, 

 the occurrence of the nuclei in pairs in the mycelium and the 

 formation of clamp-connections appear to be prerequisites for 

 fruit-body formation, but this is not so for Psalliota camj)e.stris . 

 The reduction of the nuclear groups in the cells of a fruit-body of 

 the Mushroom takes place, according to Hirmer, in the gills, and 

 is accomplished by the time the subhymenium is formed. 2 This 

 allows of a single pair of nuclei entering each basidium. Here 

 nuclear fusion takes place in the usual manner. 



There are doubtless other conditions than that of the correct 

 arrangement of the nuclei, which are necessary for the production 

 of fruit-bodies by a mycelium. It appears that a mycelium never 

 begins to form fruit-bodies until its hyphae have accumulated 

 protoplasm laden with food materials, sufficient in amount to 

 ensure that any reproductive effort shall not utterly fail through 

 lack of constructive materials. Perhaps, therefore, the mycelium 

 is subjected to an internal stimulus of such a kind that each hypha 

 has a certain effect on the whole mycelium in that it stimulates it 

 to begin the process of fruit-body formation ; and, perhaps, a 

 reproductive effort on the part of the mycelium as a whole is only 

 begun when the number of hyphae has become so large that the 

 cumulative stimulus provided by all the hyphae exceeds a certain 

 limit. 



Let us suppose that the older part of a mycelium which has 

 been vegetating for some weeks in the turf of a pasture has received 

 a stimulus of such strength that the reaction must be a reproductive 

 effort. We may take it that it is impossible for the mycelium to 

 produce fruit-bodies at once owing to the fact that the external 



1 Max Hirmer, " Zur Kenntnis der Vielkernigkeit der Autobasidiomyzeten, I,'' 

 Zeitschrijlfiir Bofanik, Jahrg. XII, 1920, pp. 668-669. 



2 Ibid. 



