554 Davis. — Cytological Studies on Oenothera. I. 
row of granules resembling a string of beads (Fig. 4). These granules are 
apparently the chromomeres of various authors. They later become no 
longer recognizable as the spirem thickens and grows shorter. The fully 
developed spirem is a deeply staining thread wound around the periphery 
of the nucleus, and at this stage generally appears continuous, although the 
structure is so small as to make the determination of the latter point very 
difficult. 
Fourteen chromosomes are formed by the cross-segmentation of the 
spirem. These may sometimes be counted within the nucleus before the 
formation of the spindle (Fig. 5). They have the form of long rods 
variously bent, as would be expected of segments derived from a coiled 
spirem thread. 
The count of the chromosomes is, however, most readily made from 
polar views of the equatorial plate (Fig. 6), where they lie in approximately 
the same plane. The chromosomes at this time are usually V or U-shaped, 
but the arms may be bent at various angles. The daughter-chromosomes 
following the metaphase of the mitosis have a more regular form, which is 
clearly shown in stages of anaphase (Fig. 7). They lie with the points of the 
V’s directed to the poles of the spindle, and in appearance are quite indis- 
tinguishable from one another. The nucleoli disappear during the develop- 
ment of the spindle, which is too small to be a satisfactory subject for 
study. 
Immediately following the organization of the daughter-nuclei the 
chromatic material takes the form of a loose reticulum, in the meshes of 
which the new nucleoli appear. As the nuclei enlarge, the strands of the 
reticulum become thinner throughout most of the structure, and the 
chromatin becomes distributed around the periphery in the form of deeply 
staining bodies of various forms and sizes (Fig. 8). These are the chro- 
matic bodies so characteristic of the resting nuclei in meristematic regions 
of the flower. 
The nuclei shown in Fig. 8 are in young pollen mother-cells of the 
fully differentiated archesporium which, as described before, generally con- 
sists of two rows of cells, with, however, frequent irregularities of placement 
probably due to the adjustment of the cells to mutual pressure. There 
follows now a long period of growth, during which the nuclei double their 
diameter and the pollen mother-cells become three or four times larger 
in diameter. An excellent idea of the extent of these changes may be 
obtained by comparing Fig. 8 with Figs. 36-39, all drawn under the same 
magnification (2,000 diameters), the latter illustrating mature pollen 
mother-cells. 
