Sexual Organs of Phytophthora erythroseptica , Pethyb. 147 
when they paid little attention to the matter, that there is a gradual 
increase from Phytophthora to Plasmopara. It seems to be so, but a 
careful comparative study would be necessary before passing final judge¬ 
ment. In the case of Pythium and Phytophthora there can be no doubt 
that the periplasm is very scanty and ephemeral. This is a point not 
generally appreciated, although it has been noticed by the earlier workers 
on both groups and by others since. De Bary (3, p. 134 ) in describing 
the genus Pythium says, for example: ‘ The space between the oosphere 
and the wall of the oogonium continues to be filled with a slightly granular, 
hyaline protoplasm, the periplasm, which may easily be overlooked.’ 
Again he says (1. c., p. 135 ) : ‘ In Pythium and Phytophthora the periplasm 
cannot be seen to take part in the maturing of the spore ; it surrounds 
it in the form of an inconspicuous, sparingly granular mass.’ Referring to 
Peronospora he says (1.c.): ‘The periplasm in the oogonium is much 
denser and more copious.’ Marshall Ward (43) describes and figures 
a very coarsely granular cytoplasm in Pythium de Baryanum and says 
that it disappears in two and a half hours after fertilization. He, as well 
as de Bary, of course, worked on living material. 
Cornu saw no periplasm in Pythium , and Hartig (19) none in Nozemia 
Fagi . De Bary (2) in his description of what he asserted to be the same 
Fungus (P. omnivor a) says that it does seem at first sight that the peri¬ 
pheral part of the oogonium is ‘ von wasserheller Fliissigkeit erfullt. Bei 
naherer Untersuchung erkennt man jedoch ringsum eine stellenweise 
ungleiche, manchmal selbst feinkornige, wolkige Trubung.’ No epispore 
is formed ; and then he says : ‘ Zuletzt zerfallt die ganze Masse unregel- 
massig in Kliimpchen oder Tropfen, welche schliesslich kaum mehr zu 
erkennen sind.’ Fischer (17) says: ‘ Pythium hat nur sehr wenig, 
vielleicht bei einigen Arten gar kein, Periplasma.’ Such examples might 
be multiplied. 
It is possibly true, as Fischer says, that in some species of Pythium 
there is no periplasm, even if there be some in others. Such a variation 
within the limits of a genus need not surprise any one, particularly a 
‘ transition ’ genus like Pythium. Monoblepharis presents the same pheno¬ 
menon. Thaxter (38) has described a species in which the whole of the 
protoplasm of the oogonium is not included in the oosphere, a portion of it 
protruding from the aperture to attract the sperms. In other species 
investigated by Lagerheim (23) the material which attracts the male cells is 
not visible, all the protoplasm being used up in the oosphere. The throwing 
out of bodies from the rounding-off eggs of species of Saprolegnia described 
by de Bary may be taken as indicating the beginning of a periplasm, and 
Butler ( 6 ) says that de Bary regarded them as homologous with such. 
The occasional finding of an exospore-like structure in Pythiopsis is to be 
regarded in the same light, as its discoverer (de Bary, 4) held. However, 
