PSALLIOTA CAMPESTRIS 419 



rudiments of spores on the tips of its sterigmata, it must be con- 

 sidered to have passed from the coming to the present generation. 

 The number and general distribution of the basidia of a coming 

 generation on any given area of the hymenium are equal to those 

 of the present generation, and it is a general rule for any generation 

 of basidia that each basidium in it shall be sufficiently well separated 

 from its neighbours to enable it to develop and discharge its spores 

 without being jostled. 



We have seen that, according to Rene Mair.e, four nuclei are 

 produced in the body of a coming-generation basidium as a result 

 of two divisions of the fusion-nucleus. According to this author, 

 two of the nuclei pass up one sterigma into one spore and two pass 

 up the other sterigma into the other spore. Then each nucleus 

 divides, so that each ripe spore comes to contain four nuclei. Maire 

 noticed, however, that sometimes the fusion-nucleus only divides 

 once, and then, he says, each spore only receives one nucleus, 

 which afterwards may divide once or twice. 1 He does not appear 

 to have observed that monosporous basidia frequently occur in 

 the hymenium of the Cultivated Mushroom. It seems to me that 

 further investigation is required to clear up the irregularity to 

 which Maire refers. It may be that, when the fusion-nucleus 

 only divides once, a single sterigma and spore are produced and 

 not two ; whereas, when there are two divisions, there may always 

 be two sterigmata and two spores formed. In any case, cytologists, 

 when studying the Cultivated Mushroom, must in future take 

 into account the fact that there are two kinds of basidia present 

 in the hymenium bisporous and monosporous. 



One of the most remarkable events in the development of a 

 basidium in the Hymenomycetes generally is the migration of the 

 four nuclei from the basidium-body into the spores through the 

 four extremely narrow sterigmatic necks. This has been studied 

 cytologically by Ruhland, 2 Maire, 3 Fries, 4 and more recently by 



1 Rene Maire, loc. cit., p. 152. 



2 W. Ruhland, " Zur Kenntnis der intracellularen Karyogamie bei den Basidio- 

 myceten," Bot. Zeit., Jahrg. 59, 1901, Abt. I, pp. 187-206. 



3 Rene Maire, loc. cit. 



4 R. E. Fries, " Zur Kenntnis der Cytologie von Hygrophorus conicus" Svensk. 

 Bot. Tidskrift, vol. 5, pp. 241-251. 



