148 Murphy .— The Morphology and Cytology of the 
the whole matter calls for further investigation, and there is no richer field 
for cytological research than Pythium and Pythium- like forms. 
From the knowledge at our disposal it is easy to see that the 
Pythiaceae and Phytophthora have on the whole a generalized type of 
sexual reproduction, one which leads to the more specialized type of the 
Peronosporaceae. The organization of ooplasm and periplasm prior to 
fertilization is developing, but it is not established so clearly as in 
Peronospora. On the other hand, the likeness of some species of Pythium 
in the mode of their sexual reproduction to Myzocytium and Lagenidium , 
for instance, as has often been pointed out, is still more striking. Pythium 
is not at the bottom of this’line of development, as de Bary held, but rather 
one at least, perhaps two or more, steps up. Morphologically there is 
little distinction between the intercalary oogonia and antheridia of certain 
species of Pythium described by de Bary and Woronin (5), and especially 
between those of P. rostratum , described by Butler (6), and the Ancylistales 
just mentioned. Cytologically the difference is not so great as is often 
imagined. In the Ancylistales the whole of the protoplasm of the male 
cell unites with the whole of the protoplasm of the adjoining female organ 
by means of a short fertilization tube before the contents of the oogonium 
have been withdrawn from the wall or organized into an oosphere (12, 44). 
It is evident that Pythium and Phytophthora are intermediate between this 
condition and that found in the Peronosporaceae. The linking up of the 
Ancylistales with this series seems to make it a logical necessity to derive 
the higher Oomycetes from the Chytridiales, and through them from forms 
like Protococcus . This line of descent has been argued with considerable 
force by Atkinson (1) recently from other premisses, and it seems that the 
points brought forward here add some degree of strength to it. The 
author realizes the many aspects of the problem, some of which are entirely 
neglected here—for example, the significance of the Monoblepharidales and 
the possible role that parasitism has played. It must be confessed that 
to the writer at least it came as a surprise to have to admit that according 
to the theory outlined above the periplasm must be an increasing structure. 
If on the other hand we hold that the lower Oomycetes have resulted 
through a life of parasitism, then we arrive at the conclusion that the 
periplasm is decreasing. This view seems to have lost much ground, based 
as it was on a false analogy of plants to animals. If parasitism is really 
responsible for the degeneration of the Chytridiales from the Peronosporales 
or the Saprolegniales (de Bary, 3 and 5), did the Fungi which are now 
parasitic on the forms from which they are said to have arisen begin by 
parasitizing their own close kin? Such a thing seems in the highest 
degree unlikely. If this has been the course of events they must have 
become parasitic on another form first and then transferred their attentions 
to other descendants from their own direct ancestors. 
