Davis.—Cytological Studies on Oenothera . II. 633 
The Reduction Divisions in the Pollen Mother-cell. 
It seems best for the sake of clearness to describe and figure separately 
the events of reduction in the anther and in the ovule. Although, as would 
be expected, the cytological features of the processes are essentially the 
same for both organs, there would necessarily be some confusion in an 
attempt to present and describe two groups of figures side by side in 
parallel series. The account of the reduction divisions in the ovule will 
be made very brief, but the series of stages will be presented in some 
fullness for comparison with the figures that illustrate the events within the 
pollen mother-cell. 
Presynapsis. The structure of the resting nucleus of the pollen 
mother-cell following the last mitosis in the archesporium of the anther is 
shown in Plate LI I, Fig. 1. As in the case of Oenothera grandijtora 
(Davis ’ 09 ) there is present besides the large nucleolus a number of deeply 
staining bodies generally distributed around the periphery of the nucleus, 
and connected with one another by very delicate strands. The nature and 
significance of these bodies are of importance in relation to current views 
that chromosomes are represented in the resting nuclei by chromatic centres 
or prochromosomes. The bodies as observed in O. biennis stain deeply 
with haematoxylin, and hold their colour tenaciously after the manner of 
chromatin. They may frequently be counted as fourteen, which is the 
number of the sporophytic (somatic) chromosomes, or in numbers somewhat 
under fourteen. Counts of deeply staining bodies in excess of fourteen may 
also be made in the nuclei, but small granules possibly nucleolar in character 
are practically indistinguishable from these bodies in the nuclei of Oenothera. 
The writer is inclined to believe that these chromatic bodies are the 
prochromosomes of Overton ( 05 , * 09 ), but it should be noted that there 
is no evidence that they are arranged side by side in pairs on a system of 
threads that might be interpreted as representing two parallel spiremes. 
The chromatic bodies of O. biennis are distributed irregularly throughout 
the nuclear cavity, but wherever two lie close together (Figs. 1, 2) the 
arrangement appears to be end to end upon a delicate strand that runs in 
the direction of their longer axes. This is possibly a point of significance 
since the chromosomes differentiated after synapsis are clearly segments of 
a single spireme and are consequently joined end to end. 
The nuclei remain for a long time in the resting condition described 
above. With the approach of synapsis the delicate strands connecting the 
chromatic bodies thicken and become much more numerous, forming a 
clearly defined network. Stages in this process are indicated in Fig. 3, 
showing a nucleus in a cell adjacent to that illustrated in Fig. 2, and also in 
Fig. 4, which shows two nuclei separated from one another by a single cell. 
The nucleus finally becomes quite filled with a dense reticulum (Fig. 5), at 
