2 1 6 Sargant. — Foi'mation of the Sexual N tic lei 
perhaps on each spindle — the segments begin to separate 
from the middle instead of from one end, and in consequence 
these segments are V-shaped in the diaster (I, pp. 465-66 : 
x Figs. 3°>3 r )- 
(2) In the succeeding division — that of both micropylar 
nuclei in the four-nucleate embryo-sac — similar deviations 
from the type occur. The spirem is distorted, and an occa- 
sional chromosome begins to divide about the middle of its 
length. The latter variation, however, is much less common 
than in the previous division (I, p. 468). 
(3) The second division of the pollen-mother-cell nucleus is 
by far the most aberrant form of the five. The spirem indeed 
is quite typical (Fig. 16). But the chromosomes are V-shaped 
from the beginning and regularly divide from the middle. 
One or two in each spindle may divide from one end. 
Consequently most of the diaster-segments are V-shaped 
(Figs. 19 and 21). 
(4) The nuclear division in the pollen-grain which divides 
the generative from the vegetative nucleus is typically homo- 
type. It agrees in every stage with the ideal series (Figs. 
24-28). 
(5) Those stages in the division of the generative nucleus 
which I have seen — namely, spirem, segmentation, and early 
spindle — are certainly homotype. The spirem is compressed 
in the pollen-tube, but not violently distorted. Longitudinal 
fission appears rather early in the chromosomes. But the close 
likeness between Fig. 33 and Diagram D cannot be mistaken. 
In describing the heterotype form of karyokinesis there 
will be no need to begin with an ideal series and afterwards 
discuss the deviations from it of the two nuclear divisons 
which follow that type. The diagrams G-M are founded 
on the first division of the embryo-sac nucleus. If they had 
been founded on the first division of the pollen-mother-cell 
nucleus, the size of the chromosomes would be greater in 
proportion to the spindle and the diameter of the nucleus. 
In all other respects the diagrams represent either division 
equally well. 
