Davis.—Cytological Studies on Oenothera. II. 
Vegetative Mitosis in the Ovule. 
The nucellus of the developing ovule presents a tissue especially 
favourable for the study of the vegetative mitoses which proved to be in all 
essentials similar to those described in the anther of O. grandiflora (Davis 
’ 09 ). The resting nucleus contains a single large nucleolus, frequently 
accompanied by one or more smaller nucleoli, and a very delicate reticulum 
in which lie small deeply staining granules of varying sizes (Fig. 58). 
Some of the granules are sufficiently large to suggest chromatic bodies 
or prochromosomes, but the writer, after many attempts to establish such 
relationships, cannot report satisfactory results. The granules are so 
variable both as to their size and number that uniform counts or groupings 
could not be made, yet it seems probable that some of the structures are 
prochromosomes. It is, however, unfortunate for the prochromosome 
hypothesis that these structures are so difficult of demonstration in the 
resting nuclei of vegetative tissues, since, if they really stand for permanent 
structures (chromosomes) of the cell, it should be possible to follow them 
with a fair degree of accuracy. 
The thickening of threads in the network (Fig. 59) indicates the 
approach of mitosis. These threads have at first a somewhat beaded 
appearance due to irregular thickenings or to associations of granules, 
but later the structure becomes more uniform (Fig. 60). Finally there 
is developed a much-coiled spireme (Fig. 61), which cannot, however, 
be traced as a single continuous thread since there are occasional points 
of union of the thread system. 
The spireme breaks up into fourteen chromosome segments which have 
at first the appearance of long, variously bent rods (Figs. 62 and 63), 
but which by condensation become much shorter and somewhat thickened. 
The chromosomes, at metaphase of mitosis, may be readily counted in 
favourable polar views of the equatorial plate (Fig. 64). The form of the 
mature chromosome is that of a more or less bent rod. 
During anaphase of mitosis the V-shaped daughter chromosomes 
are gathered into two groups with the points of the V’s directed towards 
the poles of the spindle (Fig. 65). Fallowing the reconstruction of the 
daughter nuclei (Fig. 66) the chromosomes may for a short time be recog¬ 
nized as bands or threads more numerous on the sides of the nuclei furthest 
from the cell plate, but their outlines are soon lost in the chromatic reticulum 
which is shortly developed. The reticulum is at first rather coarse and 
open, but presently becomes very delicate as the nucleus passes into the 
resting condition shown in Fig. 58. The large nucleolus which disappears 
during the mitosis is quickly formed again at an early stage in the recon¬ 
struction of the daughter nuclei. 
