; 
ij 
Igor | GAMETOGENESIS AND FERTILIZATION IN ALBUGO 93 
the superfluous nuclei have left the ooplasm (Davis 1900, fig. 3). 
This is clearly the stage nearest to zonation in character, 
therefore, although it differs much from the zonation of the 
other species in general appearance. The absence ot prelimi- 
nary protoplasmic aggregation precludes the early marshaling 
of the nuclei into the form of a hollow sphere, a phenomenon 
which is so characteristic of the zonation stage in A. Bin, A. 
Portulacae, and A. Tragopogonis. It may be for this reason, also, 
that the formation of the plasmoderma is delayed. 
The mode of development of the coenocentrum and its rela- 
tion to the oospheric nuclei remain to be considered. The 
coenocentrum was first observed by Wager (1896) in A. candida, 
and its development has been more closely followed in the same 
species by Davis (1900). The structure was given its present 
name, and its nature and history were discussed to some extent, 
in my earlier paper on A. Bit (1899). Wager (1900) further 
notes its presence in Peronospora parasitica, and observes that it 
has there an attraction for the one reentering female nucleus. 
I have already called attention to the same phenomenon in 4. 
Tragopogonis. This attraction is strikingly exhibited in A. 
candida, and demands a somewhat detailed consideration. 
A very early stage in development is shown by Davis 
(1900, fig. 2.) In a later stage the coenocentrum contracts, 
and a large globule appears at its center, much as in A. Trago- 
pogonis, with the exception that the coenocentrum is very gran- 
ular. The granules resemble the nucleoli of this species, both 
in size and stain reaction. They appear to enter the coeno- 
centrum from the ooplasm in very early stages, and may be 
seen in great numbers in the adjacent region (fig. 73). The 
nuclei at this period are in mitosis, and it is quite usual to 
see two, three, or more spindles lying with one apex imbedded 
in the coenocentrum (figs. 76, 78-20). Their form is elongated 
before their attachment, and it is evident that the coenocentrum 
possesses an attractive influence. A similar attraction has been 
observed in Peronospora parasitica (Wager 1900) for resting 
nuclei, and by myself in A. Tragopogonis; but the phenomenon 
