Pollen Mother-cells of Li Hum canadense . 193 
tuent parts are separated more widely and form a rather uniformly dis- 
tributed but very ragged and irregular reticulum (Fig. 2). There is a 
tendency for the material of the reticulum to aggregate about the periphery, 
but this tendency is not very marked as yet, and a considerable amount of 
it is distributed through the central portion of the nuclear cavity. The 
nucleolar material has considerably increased in amount and is gathered into 
large, often very irregular bodies, in contact with which is a considerable 
amount of the material of the reticulum, resulting in one or more large, 
ragged masses in the interior of the nucleus. The outlines of the nucleole 
can, however, always be distinguished in such a mass. The number of 
nucleoles in a nucleus is variable, two, three and four being common 
numbers. Fig. 3 shows a small portion of the reticulum, as seen in 
a tangential view of the nucleus. It will be seen that there is as yet 
no suggestion of a spirem-thread, but instead, irregular knots of all sizes, 
connected by narrower strands and fibres, the whole system branching 
and anastomosing in the most varied fashion. 
As the nucleus increases still further in size, the nucleolar masses 
round up and separate themselves to a large extent from the reticulum 
(Fig. 4), the material of the latter tending more and more to take up 
a peripheral position. During the period of growth of the nucleus, the cell 
has also been growing, though somewhat more slowly. The cells are 
separated by rather thin, orange-staining walls. 
After the chromatic material of the nucleus has become located almost 
wholly in the peripheral region (Fig. 5), there begins a period of rapid 
growth of the chromatin, evidenced by a marked increase in size of the 
knots ; and this growth continues until just previous to the formation 
of the spirem (compare Figs. 4, 5, and 7). The relation between fibres and 
knots, and the ragged appearance of the whole reticulum, are as yet (Fig. 5) 
little changed. Fig. 6 shows a tangential view of a portion of the reticulum 
at this stage. The nucleoles (usually two or more) are now large, approxi- 
mately spherical bodies of quite regular outline, lying in the nuclear sap, 
either entirely free from the reticulum or in contact with small portions of it. 
The nucleoles quite constantly at this stage show a number of rounded, 
lightly-stained areas in their interior. This ‘ vacuolated ’ appearance is 
first noticed after the rounding up of the nucleole and its nearly complete 
separation from the reticulum. Since these vacuoles appear so early in the 
prophases, at a time when the nucleole itself has just assumed its typical 
size and form, it seems hardly likely that their presence, in this or later 
stages, is indicative of the giving up of material by the nucleole toward the 
formation of the chromosomes. 
The nucleus, as a whole, now grows rapidly until it has reached nearly 
or quite its final size ; the knots of the reticulum (Figs. 7 and 8), having 
likewise grown considerably, lose their ragged look, because of the dis- 
