CYTOLOGICAL DISTINCTION IN FUNGI 69 
fusion with consequent doubling of the chromosome-number taking place 
on fertilisation, but actual chromosome-counting is difficult. There is, on 
the other hand, notwithstanding earlier statements which tended to locate 
reduction at the germination of the oospore, a growing opinion, based in 
part on exact counting, that the reduction in these plants is pre-sexual, 
and takes place at the maturing of the oogonium and _ antheridium. 
This receives considerable support from Trow’s results on Achiya:! he 
finds that doubling occurs as usual on fertilisation, but the necessary 
reduction takes place in gametogenesis in this plant, as in most animals, 
and not in sporogenesis, as in most plants. Such a conclusion from the 
Saprolegniae would thus correspond to what seems probable for the 
Peronosporeae: it has also been seen to be probable according to some 
writers for Vaucherta, and has been conspicuously proved for Fucus. 
In such plants the chromosome-number in the somatic divisions will be 
“en,” as in animals, and there will be an absence of cytologically distinct 
generations with obligatory alternation. 
There are various cases among the higher Fungi in which, on grounds 
of comparison of form combined with nuclear fusion, a sexual process 
is now recognised, for instance in the simpler Ascomycetes. Here the 
carpogonium has long been regarded as a female organ, and the polli- 
nodium male; a position which is now justified by the nuclear fusions 
observed. It naturally follows to regard the ascogenous hyphae as a 
post-sexual stage analogous to that in the Florideae: they hold the same 
place in the life-cycle as the carpogonial filaments of the latter. The 
condition of this stage as regards chromosome-number is still a matter 
of doubt; but there is some reason for believing that reduction may take 
place on formation of the ascospores, while their number in each ascus 
is in itself suggestive. Further observations will be required to show 
how far such comparisons have a cytological justification. 
But in the Uredineae the case for an alternation based upon cyto- 
logical detail has been fully made out for Gymnosporangium and Phragmidium, 
the facts being as follows:? The mycelium which bears aecidia and 
spermogonia has single nuclei: each is usually in a separate cell, and shows 
two chromatin-masses on division. This stage is compared with a gameto- 
phyte, capable’ of bearing sexual organs. The spermatia are held to be 
functionless male cells, and fertilisation is effected by other means. The 
young aecidium is held to be a sorus of female reproductive organs, 
each of which may be fertilised by the migration into it of the nucleus 
of one of the adjoining undifferentiated mycelial cells. The male and 
female nuclei do not fuse, however, but continue to divide simultaneously, 
and the product of fertilisation is accordingly a growth with paired nuclei: 
this condition is persistent throughout the rest of the life-cycle, includ- 
ing the aecidiospores, the mycelium which germinates from them, the 
1 Annals of Botany, xviii., p. 541. 
2V. EH. Blackman, Annals of Botany, xviil., p. 323, etc. 
