Cytology of Pythium ultimum, n. sp. 293 
certainly, and probably for the others, an erroneous one. 
There is no separation of the antheridial contents into peri- 
plasm and gonoplasm. In the oogonium, the periplasm covers 
the egg with a dense mantle at the period of fertilization, 
and makes it impossible to follow the actual process in the 
living material. The passage of protoplasm down the fertili- 
zation-tube has been assumed to be a proof that the act of 
fertilization was going on, an assumption entirely unwarranted 
now that we know the central mass is not an egg, but an egg 
covered with a thick dense mantle of periplasm. Further 
examination of Fig. 19 reveals the interesting fact that 
degeneration of the periplasmic and supernumerary antheridial 
nuclei has commenced. The degeneration is characterized 
by the assumption of greater density and great irregularity 
of form. The vesicular nuclei, in fact, appear to collapse. 
The next figure is of a section of considerable interest. 
It and one other, unfortunately insufficiently noted and passed 
over before its importance was recognized, were the only 
sections found in this condition. Of other stages, with the 
exception of that in Fig. 19, many examples have been seen. 
The egg in Fig. 20 is only partially separated from the peri- 
plasm. It is uninucleate, presumably ready for fertilization, 
and is deeply indented by the inpushing of the fertilization - 
tube. That there is a definite boundary to the fertiliza- 
tion-tube in this case, is shown by the slight plasmolysis or 
shrinking which has taken place. The other section, incau- 
tiously regarded as anomalous, and lost after making a rough 
sketch of it, showed the egg quite free from the periplasm, 
but deeply indented on one side by a swollen fertilization-tube. 
There was the same shrinking as in the previous case, but the 
egg was binucleate. One nucleus, no doubt the female nucleus, 
occupied the centre of the egg ; the other was just within 
the periphery of the egg at the bottom of the indentation, 
and immediately opposite the fertilization-tube, which how- 
ever appeared to have a closed end. The inference drawn 
from these observations is that the fertilization-tube parts 
with a nucleus at its tip, just as a tube filled with a viscous 
