Davis . — Cy to logical Studies on Oenothera . /. 561 
of prophase by the gathering of the fibrillae into two opposite sheaves. No 
centres were observed at the poles of the bipolar spindle, the fibrillae ending 
in a granular area which merged into the surrounding alveolar cytoplasm. 
The chromosomes become generally arranged in a very symmetrical 
manner to form the equatorial plate at the metaphase of mitosis. The 
condition illustrated by Fig. 37 is thoroughly typical. It will be seen that 
the sporophytic chromosomes are still joined together in pairs forming the 
rings, but they are now mostly V-shaped instead of semi-circular, the points 
of the V’s being directed towards the spindle poles. The sporophytic 
chromosomes may be readily counted at this stage of mitosis, and the 
number is fourteen, grouped of course in seven pairs derived from the seven 
rings characteristic of the prophases. The only observed irregularities of 
this arrangement (in well cut sections) were instances where one or more 
rings lagged behind the others in taking their positions in the equatorial 
plate and in completing the separation of the chromosomes comprising such 
pairs (Fig. 38). 
The V-shaped form of the chromosomes becomes even more evident 
during anaphase, as the two sets of chromosomes move away from one 
another towards the poles of the spindle (Fig. 39). Sometimes the arms of 
the V’s are brought so closely together that the line of contact might be 
mistaken for a line of premature fission in preparation for the second or 
homotypic mitosis, but this is not the case. 
The fission of the chromosomes in preparation for the succeeding 
homotypic mitosis takes place in the latter part of anaphase of the hetero- 
typic division when the chromosomes are congregated at the poles of the 
spindle (Fig. 40). The split is lengthwise of each V-shaped chromosome 
in the plane of the page on which the above letter (V) is printed. How- 
ever, at this time the arms of the V’s generally separate somewhat, so that 
most of the chromosomes are not so sharply bent as in earlier stages of 
this mitosis. This premature fission, peculiar to late anaphase, is most 
readily observed when the chromosome group at a pole is cut obliquely 
(Fig. 41) so that the chromosomes are viewed at various angles. 
There is a well-defined period of rest between the heterotypic and 
homotypic mitoses in the pollen mother-cell that is especially interesting for 
the history of the chromatin, which may be very easily followed in this 
form. The seven split chromosomes that gather at the poles of the hetero- 
typic spindle are almost always arranged so that six of them lie in a circle 
around the seventh (Fig. 42). At this time the line of fission is clearly 
marked, and the chromosomes look like seven pairs of rods when the group 
is viewed from above the pole of the heterotypic spindle, as shown in Fig. 42. 
In reality, however, the chromosomes are not rods but are V or U-shaped, 
the bent ends pointing downward or away from the pole of the spindle. 
There then develops around each group of chromosomes at the pole of 
