Cytology of Pythium nltimum , n. sp. 305 
has moreover been replaced by siphonogamy, rendering a 
further reduction possible. The siphonogamous type of ferti- 
lization is an advantageous because an economical one, even 
in the case of aquatic plants. It is interesting to note that 
Saprolegnia is nevertheless not quite perfectly adapted to its 
environment, as it still wastes a considerable number of male 
nuclei. The homologies in Saprolegnia are sufficiently clear. 
How are we to understand the case of Cystopus Blitit 
Have we any facts to help us, or are we entirely dependent 
upon our imaginative powers? The homologies seem clear 
enough until we take account of the karyology. Let us 
remember what happens so frequently in the case of the 
sporangia of Pythium and Peronospora — genera closely allied 
to Cystopus. In these two genera, the sporangia, adapting 
themselves to new environments, are converted into ‘ conidia.’ 
In some species the conversion is complete, in others, still in 
progress. Its characteristic feature is that one large coeno- 
cytic multinucleate conidium is developed in place of a 
sporangium, with an output of a number of small uninucleate 
zoospores. Does not the oogonium of Cystoptis Bliti and 
other Peronosporaceae present to us the corresponding meta- 
morphosis in the female gametangium ? I think it does, and 
we are thus able by extending the view to the antheridia 
of the Saprolegniaceae and Peronosporaceae to get a clear, 
if novel, picture of the real condition of affairs in these 
curious plants. The fertilization-tube growing out from an 
antheridium towards the egg behaves exactly like the germ- 
tube of a conidium growing towards the leg of a fly. There 
are still difficulties, however, which need further explanation. 
It is especially necessary to seek some clue to the origin 
and significance of the periplasm. We can easily imagine 
how, owing to inequalities in the numbers of female and 
male nuclei, the excess of female nuclei were pressed out 
to the periphery. Or it may have been the amount of proto- 
plasm requisitioned by each nucleus that led to this result — 
one exemplified by the Fucaceae at the present day. One 
can further imagine undesirable £ energids * being pressed out 
X 
