Homothallism and monosporous nvycelia in Coprinus. 199 
monosporous mycelia and the fertility of the compound bisporous 
mycelia. 
Hans Kniep who has also investigated the sexuality of the 
Hymenomycetes, accepts the first two of Mlle Bensaude’s 
criteria for heterothallism but not the third. He has made the 
remarkable discovery that the fruiting of a mycelium of a 
heterothallic Hymenomycete, e.g. Schizophyllum commune, does 
not necessarily depend upon the nuclei in the mycelium becoming 
paired, so that a haploid mycelium derived from a single spore 
may produce fruit-bodies resembling in external appearance and 
in the production of numerous ripe spores the fruit-bodies of 
the same species produced on a diploid mycelium derived from 
the fusion of two monosporous mycelia of opposite sex*. Hence 
the mere formation of fruit-bodies by a monosporous mycelium 
is no clear indication that the fungus is homothallic; for, not- 
withstanding its fruit-bodies, it may be heterothallic. According 
to Kniep, in a heterothallic species, the difference between a 
haploid fruit-body produced by a monosporous mycelium and 
a diploid fruit-body produced by a compound mycelium which 
has originated from two mycelia of opposite sex lies in this: that 
each basidium of a haploid fruit-body has only one nucleus in 
it when it is cut off from its parent subhymenial cell, whereas 
each basidium of a diploid fruit-body, when cut off, always 
contains two nuclei. In the haploid basidium, the single nucleus 
divides twice; whereas, in the diploid basidium, the two original 
nuclei first fuse together and the fusion nucleus divides twice. 
Thus in the haploid basidium there is no nuclear fusion, whereas 
in the diploid basidium such a fusion always takes place. 
According to Kniep, in a heterothallic species all the spores of 
a haploid fruit-body are of the same sex, whereas those of a 
diploid fruit-body are divided into groups which are sexually 
different. 
Kniept and Mlle Bensaudet, working independently, have 
both found that the formation of clamp-connections in the 
‘mycelium of any Hymenomycete is associated with the conjugate 
division of the nuclei. Hence the existence of clamp-connections 
in a mycelium is an outward and visible sign of the fact that 
the nuclei in the mycelium exist not as isolated units but in the 
paired state, z.e. as dicaryons. If, therefore, in any species of 
Hymenomycete, one finds clamp-connections always forming in 
individual mycelia of monosporous origin, one is justified in 
concluding that the species is homothallic; but if clamp- 
* Hans Kniep, Uber morphologische und physiologische Geschlechtsdiffer- 
enzierung. Verhandl. der Physikal.-med. Gesellschaft zu Wurzburg, 1919, p. Io. 
t+ Hans Kniep, Beitrage zur Kenntnis der Hymenomyceten, 111, Iv and v. 
Zeitschr. f. Botanik, vII, 1915, VIII, 1916, and IX, I9I7. 
¢ Mlle Bensaude, loc. cit. 
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