1 1 6 Mottier. —Mitosis in the Pollen Mot her -cells of 
chromatin granules are clustered about the same, as has been shown in the 
case of Lilium (Mottier, ’07), and as probably occurs in spore mother-cells 
of all plants at the corresponding stage in development. In many cases, 
however, these threads are so delicate and so few that the nucleolus appears 
to lie in the centre of a perfectly colourless space. I find no support here 
for the theory of prochromosomes, as only rarely are pairs of granules 
seen, and when the same occur they are without doubt the result of chance. 
It is a matter of common observation in all nuclei of both vegetative and 
spore-bearing cells that larger granules are frequently found to be collections 
of smaller ones. The cytoplasm is of a uniform network, with fine granules 
(Figs- 3> 4, 5)- 
At the stage of the development of the anther from which Figs. 3, 4, 
and 5 were taken there is a sharp contrast in appearance between tapetal 
and spore mother-cells, due to the greater density of the cytoplasm of the 
former, in which the granules are finer and more closely arranged. The 
writer desires to emphasize the fact that, at the stage in question, the 
nuclei of the tapetal cells have precisely the same visible structure as that 
of the spore-bearing cells, namely, fine chromatin granules scattered upon 
a delicate linin net and a relatively large nucleolus (Fig. 1), although there 
may be two nucleoli. One nucleus is present in each tapetal cell at this 
stage, but later, at about the time of synapsis, this nucleus divides, when 
each cell contains two. This binucleate condition of the tapetal cells is 
remarkably constant both here and in Staphylea , to be mentioned in a later 
paragraph (Fig. 2). At the binucleate stage the tapetal cells have enlarged 
somewhat, and their cytoplasm presents a more coarsely granular appearance. 
From the stages of Figs. 3 and 4 the nuclear net becomes more pro- 
nounced. There seems to be a greater number of meshes with thicker 
strands, and the chromatin granules are larger. The nucleolus is unchanged 
in so far as I have been able to determine. Very soon the stage of Fig. 5 
passes into synapsis. 
During the period of development described in the foregoing or in 
the presynaptic stages, Darling asserts (’09, p. 184) that the chromatin 
content is built up from material budded off from the nucleolus. The 
nucleolus, according to his view, gives off small spherical droplets, which 
migrate to the nuclear wall, where they diffuse out upon the linin to build 
up the spireme. Although small bud-like protuberances of the nucleolus 
are of frequent occurrence here and in other species of Acer examined by 
me, yet I cannot agree with Darling that this fact indicates that these bud- 
like protuberances separate and diffuse out into the net to build up the 
chromatin. However, I do not deny that the nucleolus furnishes material 
for the chromatin, as I have given expression to this idea in earlier pub- 
lications. When the nucleolus breaks up at a later stage, to be described 
below, it shows frequently bud-like protuberances, but this is merely 
