g2 BOTANICAL GAZETTE [ AUGUST 
the coenocentrum, the zone of dense cytoplasm represented in 
jig. 14 (Davis 1900, fig. 2) disappears. The rudimentary 
oosphere consists then of uniformly distributed cytoplasm, 
together with the nuclei which have completed their mitoses 
(fig. 15). This condition is characterized by the well-devel- 
oped coenocentrum, the presence of nuclei which are not in 
mitosis, and the central mass of dense, uniform, deeply staining 
cytoplasm which is suspended from the oogonial wall by delicate 
threads. Some of the nuclei now enter a second mitosis, and 
these may be found in various stages lying in this clearly 
marked central region. Those lying outside in the periplasmic 
region do not divide again, a distinction which is maintained in 
all species of Albugo. 
Before the inception of this second mitosis, during its prog- 
ress, or after its completion, the nuclei pass toward the peri- 
plasm (figs. 75-77) until all but one has left the ooplasm. The 
plasmoderma3 is now formed, preceded by the first sharp differ- 
entiation of ooplasm from periplasm. This is immediately fol- 
lowed by the wall, a condition illustrated by Davis (1900, 
fig. 46) 
What stage in A. candida corresponds to zonation in the other 
species? Is it the stage represented by fig. 7g, where the 
ooplasm is bounded by a dense layer of protoplasm ; or later 
( fig. 75) when the oosphere is somewhat more sharply differ- 
entiated; or still later when the nuclei have left the central 
region and the plasmoderma is about to be formed? The stage 
shown in fig. 74 has nothing in common with zonation except 
that the nuclei are in metaphase of the first mitosis. Zonation 
is chiefly characterized by that sharp differentiation of ooplasm 
and periplasm which precedes the plasmoderma. This char- 
acter is absent here, as well as from the stage represented in 
jig.15. A distinct differentiation does not obtain until all of 
The term plasmoderma has been suggested to me by Professor Strasburger as 4 
desirable equivalent for the much-abused Hautschicht, which was originally intended 
for purely German usage. From its relation to cell activities (Noll 1888) and its 
characteristic kinoplasmic content the plasmoderma is to be regarded as a structure 
quite distinct from that designated by the term ec/of/ast. 
