Gnomonia ery thro stoma, Pers . 601 
can no longer be traced is against such a possibility. There is circumstan¬ 
tial evidence in the case of Collema crispum in favour of fertilization by means 
of spermatia, because Baur (a) found that of the two kinds of thallus present 
in this species, that which bore both spermogonia and archicarps gave rise to 
apothecia, whereas the thallus which did not possess spermogonia only 
very rarely developed the ascus fructifications. It would seem, however, 
that until a fusion of nuclei has been observed it is not safe to conclude that 
fertilization has taken place by an external means. When the pores are 
produced between the cells of the ascogonium of Collema , that structure 
becomes a coenogamete, and development may proceed by the fusion 
of nuclei in pairs as occurs in Humaria granulata. Another possibility 
is, that only one nuclear fusion, that immediately prior to the development 
of the ascus, occurs. 
Claussen’s recent work on Pyronema confluens (6) which, however, 
requires confirmation, must be taken into consideration. He considers that 
in this species the male and female nuclei do not actually fuse in the asco¬ 
gonium but merely remain closely associated together, while in the ascogenous 
hyphae these paired nuclei divide in a conjugate manner, nuclear fusion only 
occurring just before the formation of the ascus. Blackman and Miss Fraser 
have, however, both pointed out that even if Claussen’s work holds good for 
Pyronema a mistake in the interpretation of a first nuclear fusion in the 
ascogonium can scarcely have been made in the examination of the uninu¬ 
cleate sexual organs of the Mildews, Sphaerotheca ( 22 ) and Phyllactinia ( 24 ). 
Besides, so many observers have independently recorded the fusion of nuclei 
in pairs in multinucleate ascogonial forms, e. g. Humaria granulata ( 3 ), 
Lachnea s ter core a ( 18 ), Aspergillus repe 7 is ( 9 ), Ascopkanus carneus ( 7 ), & c., 
that stronger evidence than has yet been urged by Claussen (6) will be 
needed in order to disperse the usual view of the presence of two nuclear 
fusions in many forms. The process of brachymeiosis following that of 
meiosis discovered by Miss Fraser ( 19 ) also supports the occurrence of two 
nuclear fusions in the life-history of those Ascomycetes in which this process 
of reduction has been observed. 
As has already been stated, there is no evidence that the ascogonia of 
Gnomonia are functional in that they give rise to ascogenous hyphae, the 
latter indeed appearing to arise by the subsequent differentiation of ordinary 
cells. It will be remembered that Fisch has described the degeneration of 
ascogonia in Xylaria polymorpha , so that these two Pyrenomycetes would 
appear to be similar in this respect. In Claviceps and Pleospora , according 
to Fisch and Bauke 1 respectively, the formation of female organs is entirely 
in abeyance. 
The absence of any indications of nuclear fusion in Gnomonia ery thro- 
stoma until ascus development occurs induces one to entertain the view that 
1 Bauke : Zur Entwickelungsgeschichte der Ascomyceten. Bot. Zeit., 1877. 
