3 6 9 
and of other related Primula Hybrids. 
occasionally they may both lie in the same plane. In a transverse section 
of an equatorial plate of the homotype division, the chromosomes are seen 
to be arranged in a square of three (Fig. 41). The spindles taper bluntly. 
As in the heterotype anaphase, the chromosomes, on arriving at the poles, 
form themselves into a compact mass, and then separate out once more, and 
a nuclear wall forms (Fig. 42). The chromosomes then proceed to break 
up into granules. In the resting tetrad nuclei these granules are scattered 
in the nucleus, and are joined together by fine connexions. The cytoplasm 
between the nuclei constricts, and each of the four nuclei, surrounded by its 
cytoplasm, becomes an independent cell. At the late telophase of the 
homotype division the protoplasmic threads perforating the cell-walls^ and 
joining tetrad groups to one another may still persist. The pollen-grain is 
tetrahedral in shape. 
P. VERTICILLATA. 
P. verticillata is a stronger and larger form than P. jioribunda ; the 
pollen mother-nuclei in both plants are almost identical in size, but the 
pollen-grains of P. verticillata are considerably the larger of the two. 
The resting, presynaptic, and synaptic stages are similar to those 
already described in P .floribunda. From the synaptic stages onward there 
is, however, a decided modification on the simple process adopted by 
P. jioribunda in the formation of its bivalent chromosomes, a process 
which can be clearly followed throughout its course, and is not marked by 
the confusion of the second contraction. P. verticillata , on the other hand, 
has a well-marked second contraction from which the bivalent chromosomes 
emerge. This is but another example of a feature which these Primulas 
share with the Oenotheras. Gates found a well-marked second contraction 
in Oenothera rubrinervis (15), whilst Davis saw none in O. biennis (5). 
During the early hollow spireme stage of the heterotype division, 
tracts of spireme trend together, forming a flat, deeply staining, band- 
like chromatic mass (Fig. 43). From this mass strands pass to the peri- 
phery of the nucleus. These strands are irregular in their distribution, 
vary in thickness, and anastomose freely with one another. The usual 
chromatic swellings are found at the places of anastomosis. At a slightly 
later stage the chromatic mass has further increased in bulk and is lumpy 
and thick in appearance, and from it radiate a few irregular loops of spireme 
(Fig. 44). Gradually, though the central chromatic concentration remains 
undecipherable, the escaping portions of spireme are seen to have a more 
definite arrangement and significance (Fig. 45). These may be in the 
form of loops, the univalent sides united at the apex, where there is the 
familiar chromatic swelling; or free bivalent ends may project showing 
the intimate side by side union of univalents ; or loops of univalent spireme 
may be seen, anastomosing freely, but showing no approximation of homolo- 
gous lengths. It is difficult to get a good fixation of this stage. In these 
