Chromosomes in Pollen Mother-cells . 3 1 1 
is impossible to say whether the breaking up of the chromatin into fine 
granules is a normal state or due to the action of fixing fluids. 
Soon after the last division in the sporogenous tissue, which gives rise 
to the pollen mother-cells, the nuclei pass into the resting condition, and 
both cell and nucleus begin to increase in size, the nucleus enlarging 
at first somewhat faster than the cell. The nuclear frame-work consists 
now of numerous chromatin masses of varying sizes connected into a net- 
work by slender threads (PI. XXVII, Fig. 1). These threads, which consist 
largely of linin, vary also in thickness. The thicker ones frequently retain 
the safranin more strongly, thus appearing to be somewhat in the nature of 
chromatin, and, under such conditions, a distinction between chromatin and 
linin seems very difficult to determine. One or more nucleoli are also 
present. Fig. 1 represents a rather thick section including a tangential 
view of the nucleus. Fig. 2 is a median section of a nucleus taken from 
the same anther. This figure shows that the chromatin has a peripheral 
arrangement in the nucleus, a condition which is frequently observed, and 
that the nucleolus lies in a cavity relatively free from the nuclear network. 
It is seen also that the chromatin masses are larger than in Fig. 1, and that 
their number is greater than sixteen ; hence these lumps are not pro- 
chromosomes. Two masses are frequently observed lying more or less 
closely side by side, but there is no reason to believe that such pairs are 
fusing. The delicate threads joining the chromatin masses may be found 
lying close to each other and parallel, but this does not signify that a double 
spirem is in process of formation. Inasmuch as the nuclei in all pollen 
mother- cells in an anther loculus are in almost the same stage of develop- 
ment, it is not very probable that Figs. 1 and 2 represent very different 
stages, but rather the same or very closely related stages. The greatest 
difference observed in the stage of development of cells in different loculi of 
the same anther, before the formation of the hollow spirem, was found 
at the time when the synaptic ball begins to loosen up. In one loculus, 
the synaptic mass had just begun to loosen up, as shown in Fig. 6, whilst 
in a neighbouring loculus the spirem had loosened to the extent of almost 
filling the cavity of the nucleus ; but the chromatin thread had scarcely 
become any thicker, nor had it assumed a very regular arrangement, being 
much entangled in places. If there be a difference in development between 
Fig. 1 and Fig. 4, Fig. 4 is certainly the older, i.e. further toward synapsis. 
In Figs. 3 and 4, we have nuclei that are frequently met with. In Fig. 4, 
the chromatin is in the form of small masses of a rather uniform size, and 
evenly distributed in the linin network. Each mass or granule is composed 
of very many fine granules. The nucleoli, as in such nuclei as Fig. 1 and 
Fig. 2, lie within spaces comparatively free from the nuclear framework. 
As pointed out by the writer (Mottier, J 99 ) in a paper on the effect of 
centrifugal force upon the cell, the nucleoli seem to lie within a space that 
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