949 
Oenothera Lamar ckiana and O. gig as. 
Spindle formation begins, as in biennis and grandiflora , by the entrance 
of fibrillae into the nuclear cavity following the breaking down of the 
nuclear membrane. The fibrillae likewise push out into the surrounding 
cytoplasm and thus establish multipolar spindles (Figs. 23 and 24) similar 
to those described for a number of higher plants (e. g. Equisetum , Larix , 
Lilium , &c.) ; the large nucleolus disappears at the beginning of spindle 
formation. The chromosomes still joined end to end in one or more chains 
are brought by the development of the fibrillae to the centre of the 
spindle, where they generally lie in a rather dense group, although occa¬ 
sional chromosomes may be found somewhat separated from the main 
assemblage. 
The bipolar spindle characteristic of the metaphase of the mitosis 
(Fig. 27) results from the rearrangement and gathering of the spindle fibres 
into two broad sheaves that end in granular areas which merge with the 
alveolar cytoplasm. The chromosomes may frequently be found still 
arranged in chains in the equatorial regions of the recently formed bipolar 
spindle (Figs. 25 and 26), but as the spindle grows older the chromosomes 
separate from one another, and by bending at the ends and thickening in 
the middle regions usually take on the form of thickened V’s. There 
appears to be no system in the grouping of the chromosomes as they 
are brought to the equatorial plate just previous to the metaphase of the 
mitosis. Their arrangement is quite irregular, as shown in Figs. 25 and 2 6, 
and although occasional ring-shaped pairs of chromosomes may be noted 
which were undoubtedly derived from adjacent segments of the spireme, 
most of the chromosomes become so separated that it is impossible to 
determine with certainty what was their relation to one another on the 
spireme. 
The V-shaped form of the chromosomes is especially evident as the 
two sets move away from one another towards the poles of the spindle 
(Fig. 28). However, during anaphase, as the chromosomes approach the 
poles (Fig. 29) their structure becomes complicated by a lengthwise fission 
of each chromosome (Fig. 30), which takes place in the plane of the page 
upon which the above letter (V) is printed. Thus the seven chromosomes 
that leave the equatorial plate of the heterotypic mitosis arrive at the 
poles and enter the daughter nuclei as seven split chromosomes (PI. LXXI, 
Fig. 31, PI. LXXII, Figs. 32, 33). This division is a premature fission of 
each chromosome in preparation for the second, or homotypic mitosis. 
There was found, during the study of considerable material, only a 
single case that showed numerical irregularities in the distribution of the 
chromosomes by the heterotypic mitosis. In this example eight split chro¬ 
mosomes were present at one pole of a spindle (PI. LXXI, Fig. 30), and 
six chromosomes were distributed between two sections of the other pole. 
Similar irregularities were reported by the writer (Davis, TO, p. 638) for 
