Sexual Organs of Phytophthora ery thro septic a , Pethyb . 143 
Kruger (22) found only one division in the whole oogonium, the future 
oosphere never nucleus-free, and no organized coenocentrum. The differences 
between Stevens and Ruhland on the genus Sclerospora , possibly on the 
same species, are no less marked. Similarly Trow ( 40 ) and Miyake ( 24 ), 
working on two species of Pythium in 1901, arrive at totally different 
conclusions on the arrangement of the oogonial nuclei at zonation, on the 
nature and fate of the periplasm, and on the presence of an exospore. The 
first is not perhaps of prime importance, as Kruger ( 22 ) has suggested. 
Whether or not there is one nucleus, or more than one, or none, in the 
centre of the oogonium during mitosis is more or less an accident and may 
well vary in the same species. Even when a nucleus does appear to lie 
in the central region it is not always in the exact geometrical centre, and 
the others are not all equally distant from that point. This seems to 
be a case where individual variation and the personal element are largely 
responsible for divergent conclusions. The other two points are of more 
importance—the presence of periplasm and of an exospore. Trow shows 
a zonation figure with dense periplasm and clearer ooplasm such as one 
finds in Peronospora , and later shows the oosphere entirely separated from 
the periplasm by an empty space. The periplasm is formed much in the same 
way as in Phytophthora , by the aggregation of the denser cytoplasm round 
the periphery, but it is larger in amount. He suggests that it is absorbed 
by the young spore, which is likely, seeing that it disappears without 
leaving any trace, and no exospore is formed. Miyake evidently had 
excellent material, and his drawings emphasize the similarity of behaviour 
in Phytophthora and in Pythium. Zonation is not nearly so obvious as 
Trow figured it; the periplasm is very small in amount, and at the time of 
fertilization it is almost gone. It seems clear that the author was mistaken 
in supposing that it functioned in forming an exospore, because none is 
present. What Miyake calls the exospore is possibly the primitive wall. 
Trow was probably right in this respect. 
Apart from this discrepancy the similarity of the cytological activities 
of Phytophthora and Pythium (so. far as the two species examined are 
typical) is remarkable, so much so that Miyake’s figures might almost as 
well serve for this Fungus. In both all the cytoplasm of the oogonium 
remains undifferentiated till well after division. The fertilization tube is 
formed only just before it functions and it is then short. The oosphere is 
formed in the same way, by the ultimate absorption of all the cytoplasm, 
leaving the superfluous nuclei outside. All this is in striking contrast to 
the procedure in AIbugo and Peronospora, and it emphasizes the very 
close relationship of Phytophthora to the Pythiaceae. At the same time 
there appear to be characters connecting it with the Saprolegniaceae. 
The degeneration of nuclei in the oogonium of Phytophthora prior to 
division indicates unmistakably a close relation with Saprolegnia and 
