274 RESEARCHES ON FUNGI 



two (^6) and two {aB) spores ; and (3) basidia which bear spores 

 of all four possible kinds (AB), {ah), (Ab), and (aB). In Coprinus 

 Rostrupianus ^ there is only one kind of basidium, and this bears 

 two (A) spores and two (a) spores. 



In animals and most plants, when two gametes unite, a {2n) 

 nucleus is formed in the zygote. Why then, in Hymenomycetes, 

 when two haj)lcid myceUa of opposite sex unite, are not {2n) nuclei 

 formed instead of conjugate pairs of nuclei (w)+(w) ? Why does 

 such a union of haploid mycelia result at first only in nuclear 

 association followed by a long series of conjugate nuclear divisions, 

 so that there is a delay in nuclear fusion until the basidia are 

 formed ? 



The production of (2w) nuclei when two animal or vegetable 

 gametes of opposite sex unite is correlated with the fact that every 

 gamete is a single cell and contains a single nucleus ; whereas, the 

 production of {n)-{-{n) nuclei when two hymenomycetous haploid 

 mycelia of opposite sex unite is correlated with the fact that the 

 two mycelia, when the sexual process is initiated, are usually 

 multicellular and muUinuclear . 



As we have seen, a tiny mass of hyphae of a haploid mycehum, 

 after being set at the periphery of another mycehum of opposite 

 sex 6-0 cm. in diameter, is able to diploidise the large mycelium in 

 the course of about three days. In such a physically unequal 

 combination as the one under consideration, it is obvious that the 

 nuclei of the large mycehum which receive conjugate mates during 

 the diploidisation process must be more than one hundred times 

 as numerous as the nuclei contained in all the hyphae of the tiny 

 fragment of mycehum with which the large mycehum was inocu- 

 lated. It is easily conceivable that a large haploid mycehum 

 6-0 cm. in diameter might be diploidised by a single nucleus entering 

 it from a mycelium of opposite sex. 



When two animal or plant gametes unite and form a zygote, 

 the two gametes contribute each the same number of nuclei — one 

 — to the formation of the zygote ; whereas, when two hymeno- 

 mycetous haploid mycelia of opposite sex unite and diploidise one 



1 Dorothy E. Newton, "The Bisexuality of Individual Strains of Coprinus 

 Rostrupianus,'" ibid., pp. 105-128. 



