the Ascocarp in Monasciis. 231 
As far as the difference between the young multinucleate 
sporangium and the young binucleate ascus is concerned the 
difficulty is perhaps not serious. In discussing earlier the 
nature of the ascus in various genera, it was seen that in some 
cases it was simply the fertilized ascogonium ; in others that 
it was limited to a portion of that organ, the remainder being 
cut off into separate cells ; and in others that it was a branch 
of the system of hyphae which was produced from the 
ascogonium. In other words, the result of the sexual process 
in the Ascomycetes varies, a greater or less distinction into 
fertile and sterile units being met with. The same kind of 
distinction is found in the Peronosporaceae in the germination 
of the oospore. The difference then comes simply in the ex- 
treme case to this : in the zoosporangium of the promycelium of 
Phytophthora omnivor a (assuming that the nuclear behaviour is 
similar to that of Albugo) the nuclei of the spores are different- 
iated before enclosure of the mother-nuclei in the sporangium ; 
and in the ascus of Pyronema , for example, the spore-nuclei 
are not formed until after enclosure within the ascus. That 
this difference is not seriously opposed to the idea of relation- 
ship is clear from the fact that the gameto-nuclei of the 
Oomycetes are not differentiated until after enclosure in the 
gametangia. 
The fusion of the two nuclei of the young ascus has apparently 
no parallel among the Oomycetes. It may be mentioned that 
Trow (22) found curious ‘ double ’ nuclei in germinating 
oospores and conidia oiPythium ultimum , which may represent 
pairs of nuclei in the act of fusing, but whose significance is 
entirely obscure. The only other fusions which have been 
observed in that group are the sexual fusions in the oogonia. 
However, since the meaning of the fusions in asci does not 
seem to have been satisfactorily determined, the exact bearing 
of the phenomena on the question of relationship cannot be 
estimated at present. 
In the foregoing discussion stress has been laid upon the 
analogy of spore-formation in oogonia and asci. The periplasm 
of both organs ought, therefore, to be regarded as having 
