472 Fraser and Welsford . — Further Contributions to the 
the Ascomycetes in a new sense, held the ascus to be an egg in which 
fertilization occurred, and regarded the archicarp and antheridium, when 
present, as merely vestigial. 
In 1895 Harper (16) reinvestigated Sphaerotheca humuli ; he was able 
to observe the fusion of a male and a female pro-nucleus in the oogonial 
cell of the archicarp, and further to confirm, for this species, Dangeard’s 
statement that a nuclear fusion takes place in the ascus. The existence 
of two fusions in the life-history of the Ascomycetes was thus recognized 
and has since been confirmed, among normally sexual species, in Erysiphe 
(Harper (17)), Pyronema (Harper (18)), Boudiera (Claussen (5)), and Phyl - 
lactinia (Harper (19)), and among pseudapogamous forms in Humaria 
granuiata (Blackman and Fraser (2)), Ascobolus (Welsford (22)), Lachnea 
(Fraser (12)), and Humaria rutilans (Fraser (13)). In all these fungi the 
two fusions have been actually described, while strong evidence of their 
occurrence has been brought forward in a number of others. 
In 1907 Claussen (6), in a preliminary paper, re-described the develop- 
ment of Pyronema confiuens. He stated that the nuclei pair, without 
fusing , in the ascogonium, that they travel in pairs, dividing conjugately, 
up the ascogenous hyphae, and eventually fuse in the ascus. Claussen 
concludes that a single fusion, that in the ascus, occurs, and that it repre- 
sents the ultimate union of male and female pro-nuclei first associated 
in the ascogonium. He regards it as exactly comparable to the fusions 
in the teleutospore and basidium, and as forming, like these, the completion 
of a sexual act initiated at an earlier stage. 
This may imply, as Claussen seems to think, a definite contraversion 
of the fusions observed by earlier workers and by himself (5), and his 
generalization is so far satisfactory that it brings the Ascomycetes into 
line with the Uredineae and other Basidiomycetes, and does away with 
the difficult question of the significance of the second, or so-called asexual, 
fusion. 
It might perhaps be conceivable, in accordance with this view, that 
confusion should have arisen, in earlier work, with regard to the behaviour 
of the minute nuclei of the coenogamete, but it seems to us improbable 
that the sequence of stages in uninucleate forms, such as the mildews, 
should have been misinterpreted. In these species not Only has the first 
fusion been observed, but a stage has been several times recorded (Harper 
(16), (17), (19), Blackman and Fraser (1)) when the antheridium is already 
empty and the oogonium contains a single nucleus ; such a stage follows 
the entrance of the male nucleus into the oogonium and obviously implies 
fusion. 
Claussen’s views, moreover, as applied by him to Ascomycetes in 
general, are difficult to reconcile with the observations recorded both here 
and previously, as to the reduction phenomena in the ascus. 
