314 Motiier . — The Development of the Heterotypic 
stage of synapsis does not present the sharp contour that is seen in the 
resting nucleus. On the contrary, it is very delicate and appears to be 
composed of a network of very delicate fibrils, or as a mere cytoplasmic 
boundary of the nuclear cavity. The nucleus must have, however, a distinct 
membrane of its own, for when one observes, for example, the male nucleus 
in the cytoplasm of the egg or in the cavity of the embryo-sac, one can 
scarcely conclude otherwise. Just how long the condition of synapsis per- 
sists cannot be stated definitely. The time undoubtedly varies with the 
rapidity of growth and may depend upon growth conditions. The writer 
has observed that pollen mother-cells of Lilium divide rapidly on bright 
warm days, while in cool cloudy weather the process went on much more 
slowly. The synaptic period represents probably the longest pause in the 
mitotic process, but the exact duration and the conditions regulating 
the same are matters yet to be determined. 
As stated above, no definite structure can be made out with certainty 
in the mass when synapsis is complete, but as soon as the mass begins to 
loosen up, as is manifested by the extension into the nuclear cavity of, at 
first, a few, then several loops or turns of the spirem (Fig. 6 ), it is clearly 
seen that a definite spirem is present which is split lengthwise, as evidenced 
by the occasional divergence of the halves, or by the presence of two 
rows of chromatin granules or chromomeres. However, a double row of 
chromomeres cannot always be seen in the free portions of the spirem that 
first project from the contracted mass. Up to the time of synapsis, the 
pollen mother-cells are polygonal in form, fitting together in complete 
tissue connexion, but, as soon as the synaptic mass of the nucleus begins to 
loosen up, the cells round off at the corners, and in a short time they will 
have separated from the original walls and have formed the new walls so 
characteristic of these cells. As stated in my earlier publication, the 
original, delicate walls of the cells persist for some time after the pollen 
mother-cells have contracted away from them. The rounding up of the 
pollen mother-cells seems to be brought about both by the contraction of 
the protoplasm of the cells and by the enlargement of the anther through 
growth. With the further increase in size of the loculus, the cells soon 
come to lie loosely in the cavity. Before describing the phenomena 
immediately following synapsis and the final formation of the chromosomes, 
the presynaptic history in Lilium will be given. 
Lilium, Shortly after the organization of the daughter nuclei, resulting 
from the last somatic division in the sporogenous tissue, the chromosomes 
begin to reticulate into smaller masses. One or several nucleoli may be 
present, usually more than one. The nucleus now presents a structure 
consisting of irregular lumps or masses of chromatin, varying in size and 
held together by linin threads or strands (Fig. 15). Many of these linin 
strands are thicker than at a later stage and retain the safranin strongly.. 
