Sexual Organs of Phy top hthora ery thro septic a, Petliyh. 145 
is being laid down. This is in opposition to the findings of all other 
authors and it is fairly certain that it does not occur: it is possible he 
mistook fusion stages in the spore for divisions, neither of which is figured. 
The continuation of the uninucleate condition of the oospore throughout 
the resting period might be construed as an extension of the tendency 
found in the genus Albugo, A. Portulacae and A, Bliti are multinucleate 
throughout. A. Tragopogonis and A, Candida have oospores which are 
uninucleate for a short time only. The oospore in the genus Peronospora 
is uninucleate all through the resting period. 
This fact, coupled with a certain degree of resemblance during zona- 
tion, appears to present some cytological evidence of relationship between 
Albugo and Peronospora, There is other evidence derived from the same 
source, however, which tends to emphasize the relationship of Peronospora 
to the other genera of the Peronosporales. This is of course the general 
view based on morphology alone, and for that reason it is doubly likely 
to be the right one. These genera, Pythium , Phytophthora , Sclerospora y 
and Plasmopara , have not been investigated very fully, but enough has 
been done to show that they are very closely related. One point in 
particular of considerable importance has been well established but not 
sufficiently appreciated. That consists of the marked difference between 
them and the genus Albugo in the appearance of the cytoplasm in the 
oogonium, the late appearance of zonation, and the small amount of 
periplasm which they all possess. 
Stevens ( 36 ), who worked on an unnamed species of Sclerospora y and 
Ruhland ( 32 ), who investigated S, graminicola , are in considerable dis¬ 
agreement on several points, but they are in fair agreement on the question 
which more nearly concerns us here. Both refer to the lack of differentia¬ 
tion of ooplasm and periplasm in the early stages of nuclear division. 
Stevens found that zonation set in later, and he figures an undoubted 
periplasm both after division and when the spore is maturing, which is, 
however, less than in Peronospora or Albugo. Ruhland, some of whose 
drawings of the formation of the oosphere and the extrusion of the 
superfluous nuclei in the oogonium rather resemble those of Phytophthora y 
suggests that the periplasm is absorbed to feed the spore, since the 
exospore is so small; and in no case does he show it after fertilization 
is accomplished. 
Much the same thing is found in the genus Plasmopara y which is 
evidently very near Sclerospora, Ruhland ( 1 . c.), who treats of both in 
the same paper, makes use of practically the same words to describe 
them : there is no differentiation of the oogonal cytoplasm during division ; 
the periplasm is scanty, and he suggests that it is used up to form the 
endospore. There is very little shown in the figures. Rosenberg’s ( 31 ) 
account and drawings on the same point in Plasmopara are quite con- 
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