144 Murphy .— The Morphology and Cytology of the 
Achlya at least, where the same thing has been found to occur. This 
assumes that the account of all previous workers on the Peronosporales, 
where it has not been found, to be correct. It would not be surprising to 
find that it took place in Pythium at least. 
It is less easy to analyse from the standpoint of their respective 
nuclear behaviours the relationship of Phytophthora to the remaining 
Peronosporales. This is partly due to the obscure relation of these to 
one another and partly to discrepancies in their various cytological 
histories. In the first place, it is evident that the Albuginaceae stand 
apart. This is supported on morphological and parasitological evidence. 
Whether they lead up through A. Candida and A. Lepigoni to Peronospora 
is another question. It is easy to recognize an oogonium of either genus 
from its cytology alone; they belong to different groups. In Albugo the 
ooplasm is very dense and is separated from the periplasm by a very 
sharp line of demarcation, along which the dividing nuclei lie. Peronospora , 
on the other hand, has its periplasm denser than the ooplasm ; the dividing 
line is not so sharp; and the nuclei do not lie so regularly on it. Further, 
in the lower species of Albugo , those with multinucleate ooplasm, there is 
always a second division of these nuclei, according to Stevens ( 34 , 35 ). 
The same author states that the ooplasm nucleus of A. Candida divides 
a second time also ( 35 ), but in this he is at variance with Davis ( 14 ) and 
Kruger ( 22 ), the latest worker on the group. Indeed, leaving the above- 
mentioned lower species of Albugo out of account, the weight of evidence 
is gradually coming round towards establishing only a single division in 
each of the sexual organs. Some of the earlier workers were obsessed 
with the idea that there must be a reduction division at that point, and 
it is wonderful what can be seen under such circumstances. It has now 
been shown on fairly good evidence in the case of Saprolegnia (Claussen, 8) 
and- Albugo (Kruger, 22 ) that reduction takes place in the first division 
of the fusion nucleus, and this no doubt holds true for the whole group. 
The second division is intelligible in Albugo Bliti , A. Portulacae, and 
A. Tragopogonis , but hardly in a form like A. Candida. While, if it may 
be accepted that the latter has only one division, it certainly shows signs of 
a possible connexion with Peronospora. 
All workers on Pero7iospora agree that there is only one division in 
both sexual organs, and that the cytoplasm about the same time is sharply 
divided into two zones—an inner vacuolar and an outer denser area, the 
periplasm. On all other essential points the authors are in unanimous 
agreement also, with the exception that Kruger ( 22 ) shows that the 
structure described by Wager ( 42 ) and Ruhland ( 32 ) as a coenocentrum 
is merely the irregular little mass of cytoplasm that is sometimes found 
in the centre (Zentralplasma) . Kruger describes too, without figures, 
a repeated division of the oospore nucleus while the wall of the latter 
