Fertilisation and Alternation in the Uredinece. 25 
their feeble power of germination (a total absence of power of 
germination is, of course, not a necessary character of male cells), 
the conclusion seems inevitable that the spermatia are male cells, 
which formerly played a part in connection with the aecidia, but 
have now become quite functionless. 
The alternation of stages with single and paired nuclei was 
fully confirmed as was also the fact that the transition takes 
place in connection with the aecidium. The development of the 
very simple and probably primitive aecidium of P. violaceum was 
followed out in detail; it arises as a layer of rectangular uninucleate 
cells just beneath the epidermis of the leaf. Each of these cells 
becomes divided into a short sterile cell above, which soon degen¬ 
erates, and a fertile cell below, which increases in size, becomes 
binucleate and gives origin to a row of binucleate aecidiospore- 
mother-cells, which divide and form binucleate aecidiospores and 
intercalary cells. Thus the condition of paired nuclei starts in the 
fertile cell and is continued to the teleutospore. The fertile cell, 
however, becomes binucleate, not by division of its original single 
nucleus, but by the migration through the wall of the nucleus of a 
neighbouring vegetative cell of the mycelium. 
The fertile cell has the characters of a female cell; it cuts off 
a sterile cell, and it is stimulated to further active development by 
the entrance of a nucleus from without. It is accordingly im¬ 
possible to consider this process other than as one of fertilisation, 
for the delay in fusion of the nuclei has its parallel among certain 
animal eggs (e.g. Cyclops). In the absence of spermatia this process 
might be looked upon as a simple form of ordinary fertilisation in 
which the male cell was undifferentiated and there was no complete 
fusion of the two cells. In the presence, however, of the spermatia 
with their special cytological characters, etc., the only view that 
seems capable of explaining the facts is that the fertile cell (=female 
cell) was formerly fertilised by the spermatia, but that now the 
process has become reduced, fertilisation by means of spermatia 
having been replaced by the more certain method of fertilisation 
by the nucleus of a neighbouring vegetative cell. This process is 
probably to be looked upon as intermediate between the normal 
process of fertilisation with differentiated male and female cells and 
that observed recently by Farmer, Moore and Digby in the case of 
apogamous ferns, where both acting male and female cells are 
ordinary vegetative cells. 
If the view be accepted that the spermogonia represent male, 
