473 
Cytology of the Ascomycetes. 
On the other hand, it has already been noticed that in pseudapogamous 
forms fusion may be delayed till the nuclei are just leaving the ascogonium, 
and that in H. rutilans it occurs in the ascogenous hyphae ; it seems 
possible, then, that in Pyronema conjhiens , the fusion may sometimes be so 
much retarded as to actually take place in the ascus. There is, however, 
necessarily no proof that the large nuclei figured by Claussen in the as- 
cogenous hyphae are not the result of fusion, even though .they travel 
towards the hymenium in pairs, and though the later fusion stages were 
not seen. 
In view of these various possibilities, a full account of the ascus 
divisions in Pyronema conflnens would be of very great value and would 
no doubt solve the problem of nuclear fusion. It is quite to be expected 
that, in some Ascomycetes, one of the fusions should have been 
abandoned ; and the conditions under which this may take place will 
be of considerable interest ; it will also be of value to observe whether 
the method of reduction retained is the meiotic, which appears to represent 
the last stage of fertilization, or the brachymeiotic, which may be regarded 
as compensating an asexual fusion. 
Sexual and Asexual Fusions. 
In this connexion the distinction is of interest between asexual fusions 
and fusions which may be regarded as sexual in the widest sense. Fertiliza- 
tion, in all cases studied, is followed by a meiotic phase, the distinguishing 
characters of which appear to be (i) a contraction phase during which the 
chromatin filaments are temporarily massed ^together ; (2) a longitudinal 
fission throughout the length of the spireme (this fission, though occa- 
sionally obscured, persists till the homotype metaphase, when it forms 
the line of separation of the daughter-chromosomes) ; (3) a second or 
synaptic contraction. Here the chromosomes become closely massed 
together, and, as the contraction loosens, their number, or that of the 
corresponding loops, may be counted. 
Brachymeiosis is more variable ; its most essential feature seems 
to be the formation of a given number of chromosomes, half of which pass 
to each daughter-nucleus. These chromosomes may be apparently inde- 
pendent or they may be paired at the beginning of the brachymeiotic 
division as in Otidea aurantia , or at an earlier stage as in Peziza vest- 
culosa and Phyllactinia ; such pairing, in the two former cases, is asso- 
ciated with a contraction phase. 1 It seems, therefore, that some mechanism 
exists for the orderly distribution of allelomorphs. 
1 I have re-examined part of the material of Humana rutilans from this point of view, but 
without finding a contraction either in the second or the third prophase. Such a result is quite to be 
expected, as there is no obvious pairing of the chromosomes in this species. — H. C. I. F. 
