rave MARCUS M. HARTOG. 
The last two genera have a mycelium unusually well deve- 
loped for this group, and are regarded by De Bary as doubtful 
members thereof. 
Mownosrepuaris! forms its spermatozoa by the resolution 
of the protoplasm of spermatangia into one-flagellate cells, 
differing only in their smaller size from the vegetative zoo- 
spores, and therefore possibly formed by bipartition of potential 
zoospores. The protoplasm of the oangium, after forming a 
terminal aperture, contracts and rounds off into the oosphere ; 
which, if uninucleate, has probably, from its size, formed its 
gametonucleus by the fusion of many vegetative nuclei. No 
epiplasm is apparently formed. 
The PrRoNosPpoREZ are oogamous and siphonogamous. 
The only species in which the formation and union of the 
gametes has been fully studied is Peronospora parasitica; 
and I shall utilise Wager’s careful description” of the sexual 
processes in this species, having had the opportunity of verify- 
ing its accuracy on the original specimens. The spherical 
“ oogonium ” (or rather oangium) is cut off from the tubular 
hypha by a basal septum if terminal, by two if intercalar; 
it is apocytial, containing numerous nuclei. Each nucleus 
undergoes repeated bipartition; and the majority of the nuclei 
so formed pass into a peripheral layer of protoplasm, thus 
constituting the so-called “periplasm ;” three of them pass to 
the middle of the central mass of protoplasm, the so-called 
“ gonoplasm,” and fuse therein into the single pronucleus. 
The “ antheridium ” (or spermatangium) is an ovoid enlarge- 
ment of a hypha, closely applied by its apex to the oogonial 
wall and cut off by a basal septum ; it contains several nuclei, 
which like those of the ‘“‘oangium” multiply by mitosis; it 
emits a tube which perforates the oogonial wall and passes 
through the periplasm to open just at the surface of the gono- 
1 Cornu, “Monographie des Saprolegniées,’ in ‘Ann. Sci. Nat. Bot.,’ 
ser. 5, vol. xv. 
9 
2 “On the Structure of the Nuclei in Peronospora parasitica,” in 
‘Annals of Botany,’ vol. iv (1889). 
