145 
Lloyd Williams. — Studies in the Dictyotaceae. 
The septum dividing the stalk-cell from the sporangium proper soon 
makes its appearance, and the separation of the tetraspore mother-cell 
is completed. 
The First, or Reducing Division of the Tetraspore 
Mother-cell. 
Before the initiation of the spirem the nucleus passes through a similar 
condition to that shown in Fig. i, where the reticulum easily separates 
from the nuclear membrane. Soon, however, there is a very thin convoluted 
spirem distributed through the nuclear cavity. The fine granules upon 
this stain but feebly as yet, but here and there a few larger, but still small, 
deeper-stained bodies appear between the threads (Fig. 7). The nucleolus 
preserves for a time the fibrillar appearance already described, but as the 
spirem develops a vacuole appears in the former with, at first, a few smaller 
ones. Soon, however, there is only one fairly large vacuole which has 
a firm, deeply staining outline, and there are darker staining granules 
within it. The axis of the nucleus is once more parallel with that of 
the thallus, but the poles can only be distinguished with great difficulty 
owing to the faintness of the radiations (Fig. 7), and the centrosomes, 
if they exist at all, are not distinguishable. No signs were seen at this 
stage of the division of the centrosome, nor could the change of position 
of the nuclear axis be followed. The spirem gradually becomes more 
prominent, and shows a tendency to aggregate near the poles. A deeply 
staining spherical or sometimes angular body, considerably larger than 
any of the granules hitherto described, now makes its first appearance. 
It is peculiar to this mitosis, and it persists till after the splitting of the 
spirem (Figs. 8-12). It is always present during these stages, and there 
is hardly ever more than one. Whether it directly separates from the 
nucleolus or is formed by the fusion of the smaller granules shown in 
Fig. 7 could not be decided. The body will be designated for the present 
the chromophilous spherule. It should not be confused with the nucleolar 
globule which appears during several of the mitoses in this plant. The 
faintly staining cloudy nucleoplasm which appears during the synapsis 
is absent from this stage. 
The above condition leads directly to the very interesting knot stage 
or true synapsis , which forms a most striking feature in the cytology of the 
reduction stage, but appears nowhere else in the whole history of the plant. 
Mottier 1 says : * During the prophase of both divisions in the tetraspore 
mother-cell the behaviour of the chromatin differs strikingly from that 
in the higher plants. There is not developed here a regular and continuous 
chromatin-spirem which segments into the chromosomes, but these arise 
as isolated masses often differing much in size. It gives the impression 
1 1900, l.c., p. 188 . 
L 
