Igor] GAMETOGENESIS AND FERTILIZATION IN ALBUGO 245 
of a large zone of darkly staining cytoplasm which contains at 
its center the alveolar (trophoplasmic) region. This region sel- 
dom contains a globule such as characterizes the other three 
species. In A. Aft the structure is much more prominent and 
endures for a longer period. It is of more complicated struc- 
ture than in A. Portulacae, owing to the presence of a distinct 
central globule. In A. Tragopogonis the coenocentrum is still 
more highly developed. The central globule seems to be formed 
by the trophoplasm of the central region, or rather by the coa- 
lescence of the contents of its vacuoles. This globule in a later 
period becomes granular, the granules staining like nucleoli. 
A. eandida possesses the most highly developed coenocentrum 
which, while closely resembling that of A. Zragopogonis, differs 
in that from its earliest formation till near the end of its func- 
tional activity it is thickly beset with coarse granules (jigs. 73, 
77) that in size and stain reaction agree with the nucleoli of this 
species. 
In its function as well as structure this organ advances in 
complexity in the series here presented. In A. Portulacae there 
is no extensive accumulation of nutrient material in the vacuoles 
of the trophoplasm. In A. Bét this accumulation is marked. 
In A. Tragopogonis the central globule shows strong chemotactic 
attraction for the nuclei and serves as nourishment for one or 
more of them. In A. candida this function of nutrition reaches 
greater perfection, as is shown by the attachment of the nuclei 
to the coenocentrum rather than their mere approximation to it. 
The coenocentrum develops earlier in the more highly differen- 
tiated species, and thus by exerting its attractive influence upon 
the nuclei before zonation strongly influences ontogeny. It has 
likewise probably been an important factor in changing the gen- 
eral character of oogenesis in phylogeny. 
The presence of the receptive papilla in the four species of 
Albugo, as well as in Peronospora (Wager 1900, p. 270), attests 
to its importance either in the present or in ancestral species. 
Young stages in the development of this structure show that 
the plasmoderma adheres to the wall immediately under the 
