194 
Wager . — The Life- history and 
primarily for the purpose of increasing its vegetative activity, and the fusion 
of the generative nuclei is apparently not essential to the maturation of the 
zygote, but seems to be required for the production of the zoospores. 
The obvious explanation that may be given of this is that the zygote 
is essentially a resting cell in which large quantities of food in the shape of 
fatty substances and glycogen are stored up in order to tide over a period 
of rest and to afford food material for the growth of the sporangium which 
will ultimately be produced, and that for this purely vegetative develop- 
ment the vegetative portions only of the nucleus are required. 
This is also very clearly shown in the Uredineae ; but here, instead of 
a resting stage, a long series of vegetative cell divisions is interposed 
between the cell fusion and the nuclear fusion. The cell fusion, or, as 
Blackman calls it, ‘ vegetative fertilization’, takes place here by a sexual 
process in the aecidium, the contents of one cell passing over into the other. 
The two nuclei come together, but do not fuse. During the long series of 
vegetative divisions which intervene between the germination of the zygote, 
or what represents the zygote, and the germination of the teleutospore, they 
remain separate and divide continually by conjugate division. In the 
teleutospore the direct descendants of these two nuclei fuse. 
The binucleate phase of the Uredineae is commonly regarded as 
a sporophyte in which the cells contain % n chromosomes. But inasmuch 
as the nuclei remain separate all through, it is plain, as Harper points out 
(TO), that the nuclear fusion is unnecessary so far as the sporophyte is 
concerned, and that its vigour and adaptability are not dependent upon 
the union of the parental chromosomes into a single nucleus. But as soon 
as the time arrives for the actual reproductive organs to be formed, the 
fusion takes place. The process of conjugate division in the Uredineae is 
accompanied by the extrusion of nucleolar chromatin which is probably 
homologous with the chromidia of Polyphagits. 
The Hymenomycetes may be brought into line with the Uredineae, 
for although there appears to be no true sexual fusion, the cells of the 
hymenium become binucleate, probably by a process of autogamy, similar 
to that which probably takes in the simpler forms of the Uredineae, and the 
binucleate condition persists until the formation of the binucleate basidia, 
in which the two nuclei fuse. 
The general conclusion at which we arrive, therefore, is that when the 
sexual cell fusion is followed by a period of rest, as in P olyphagus , or by 
a series of vegetative cell divisions, as in the Uredineae, there is no necessity 
for any nuclear fusion, but that as soon as the reproductive spores are to be 
formed, the fusion takes place and completes the sexual fusion. 
Here we are met with the anomaly in the life-history of the Ascomy- 
cetes, that in their case there appear to be two complete nuclear fusions, 
one in the ascogonium and one, later on, in the ascus. Gaussen, in his 
