Chromosomes in Pollen Mother-cells. 
32i 
of chromatin and linin, but that the chromomeres arc held in the linin. 
Each chromomere has a rough outline, as if erosed, which seems to indicate 
that each is made up of smaller granules. The chromomeres were not 
observed in the form of angular blocks or masses, as figured by Allen (’ 05 ). 
In some parts of the thread the chromomeres are seen to be regularly 
paired and of the same size ; but in other parts they may be different in 
size, some being much smaller than the average, and not paired but 
arranged alternately. Whether this is due merely to the twisting of the 
spirem cannot be stated with certainty at present. Fig. 2 5 a represents 
a portion of the spirem at the stage of development in question, as the 
writer has observed it. 
After the stage of Fig. 26, the spirem becomes slightly thicker, and 
always stains as a more uniform thread in which the double nature cannot 
always be made out ; but frequently the double character of the thread is 
apparent, and it is seen that the two segments are twisted about each other 
(Fig. 2 6 ). In preparations of this stage of mitosis, cases in which the 
longitudinally split spirem tends to diverge are the exception rather than 
the rule (Fig. 26). The rule seems to be that the halves of the spirem are 
so closely applied to each other as to conceal nearly, or quite, the double 
nature. 
From the stages shown in Figs. 25 and 26, the spirem soon passes 
into the condition which has been described as the second contraction 
(Figs. 27, 28). In these figures it is apparent that the larger part of the 
spirem is arranged in loops which tend to radiate from the centre of the 
nucleus, where the thread is already somewhat closely entangled. In this 
stage, however, as will be mentioned in a subsequent paragraph, the sister 
threads do diverge considerably in many instances. 
When the chromatin thread, as it emerges from the synaptic mass, 
is compared with the presynaptic phenomena, certain changes seem to 
have occurred in the interval, although it is not possible to determine even 
in very thin sections what actually takes place in the dense contracted 
mass. The writer assumes that all nuclei pass through this stage, and he 
has limited the term synapsis to this contraction. Judging from figures 
of other observers, this term seems to have been made to include the 
loosening up of the spirem, and thin tangential sections of the early stages 
of the loosening mass have been doubtless looked upon as indicating what 
occurs in the tightly balled-up nuclear contents. Now when we compare 
the chromomeres in the spirem, as it emerges from synapsis (Figs. 6, 24), 
with the chromatin masses, as they appear in certain cases at the beginning 
of the contraction (Fig. 22), it is clear that these masses of chromatin are 
very much larger than the chromomeres. There must take place then, in 
cases like Fig. 22, a further reticulation into smaller granules. In such 
cases there would be as good ground for the conclusion that a double 
