924 Gates.—Pollen Formation in Oenothera gigas. 
polar view, and shows one of the early anaphase groups of fourteen 
chromosomes. 
PI. LXIX, Fig. 39 is a later anaphase of the homotypic spindle in oblique 
view, showing the group of fourteen chromosomes on their way to the lower 
pole. Only twelve of those approaching the other pole are to be seen, on 
account of the upper end of the spindle being obliquely cut. In that case it 
can be seen that the daughter chromosomes are partly looped or V-shaped, 
but some are long and rod-like, while others are short and rounded. There 
is thus also much variation in the shape of the chromosomes at this time, 
and this may apply to the chromosome group on a single spindle, as in 
Fig. 39. PI. LXVIII, Fig. 40, shows a somewhat later homotypic anaphase 
in side view. The chromosomes here also show some variation in shape, 
but are mostly rather straight and somewhat elongated. Fig. 41 shows 
a homotypic spindle in anaphase, in which nearly all the daughter chromo¬ 
somes are clearly constricted in the middle, and sometimes appear as 
though a definite transverse fission had taken place. 
It has already been mentioned, in connexion with the synaptic stages, 
that different anthers of the same flower not infrequently show different con¬ 
ditions. A remarkable case of this kind has been observed in the pollen 
mother-cells during the homotypic mitosis. PI. LXVIII, Figs. 33 and 35 ; 
PI. LXIX, Fig. 37 ; PI. LXVIII, Fig. 34 ; PI. LXIX, Fig. 39 ; PI. LXVIII, 
Figs. 40 and 41 are all taken from one flower. Of these, the first three are 
from one anther and the last four from another. A remarkable and constant 
difference was found between the pollen mother-cells of these two anthers. 
These differences (as can be observed from the figures) are (1) in the 
breadth of the spindles. In one anther (PI. LXVIII, Figs. 32 and 35 ; 
PI. LXIX, Fig. 37) these are very narrow, so much so that there is sometimes 
scarcely room for the chromosomes on the equatorial plate, and they project 
beyond the sides of the spindle, as in PI. LXVIII, Fig. 32. These chromo¬ 
somes also frequently fail to show their bivalent character at this time. In 
the other anther (Figs. 34, 40, and 41 ; PI. LXIX, Fig. 39) the spindles are 
remarkably broad, and it would appear (although this is not certain) that the 
number of spindle fibres must be greater. The chromosomes usually appear 
as clear bivalents on the equatorial plate. This difference in the spindles 
was very striking and was found to be constant between different anthers. 
(2) While the walls of the mother-cells in anther no. 1 were smooth and 
even, as they ordinarily are, yet in anthers having the broad spindles already 
described the walls were always very irregular, showing extensive growths 
or proliferations subsequent to the separation of the mother-cells which 
takes place usually soon after synapsis. The character of these growths 
of the cell-wall can be judged from PI. LXVIII, Figs. 28 and 34 ; PL LXIX, 
Figs. 38 and 39. This difference between pollen mother-cells is therefore 
not merely a matter of variation, but the broad homotypic spindles and 
