9 i 6 Gates.—Pollen Formation in Oenothera gigas. 
with a process which may prove to be of fundamental significance in con¬ 
nexion with the period of meiosis. This process will first be described. 
After the synaptic nucleus of the pollen mother-cell has reached the 
side of the cell, an extrusion of material from the nucleus into the cytoplasm 
of the adjacent cell has been observed to take place. PI. LXVII, Fig. 8 shows 
a row of pollen mother-cells in which this process is happening simultaneously 
in all the cells. In Figs. 9 and 10 the same process is shown under higher 
magnification. It will be seen that material is being extruded from the 
spireme of each nucleus, through an opening in the cell-wall into the 
cytoplasm of the adjacent pollen mother-cell. The nucleolus is always 
present at this time as a large spherical body, but in my observations 
I have never found it to take any part in this extrusion. The nucleus at 
this time is usually so placed that a considerable area of the nuclear 
membrane is in direct contact with the cell-wall, or perhaps the membrane 
may disappear over this area, leaving the nuclear contents in direct contact 
with the cell-wall and, through the openings in the wall, with the cytoplasm 
of the adjacent cell. The extrusion may take place through a single 
opening or (perhaps more frequently) through several. 
In a previous paper (Gates, ’ 08 ) I showed that rather large and con¬ 
spicuous protoplasmic connexions occur between the pollen mother-cells 
in Oenothera . They doubtless occur in all the forms, as I have demon¬ 
strated them in several. Fig. 13 shows the connexions between two 
mother-cells of O. gigas in the condition of synizesis. It will be seen 
from this figure that they vary greatly in size. They are usually less 
numerous than in the figure, three or four being perhaps the most frequent 
number seen on one cell-wall. These connexions have never been observed 
on the walls separating the mother-cells from the tapetal cells, and ap¬ 
parently they only occur between mother-cells. Regarding the origin of 
these cytoplasmic connexions, they have not been traced to an earlier stage 
than the synaptic mother-cell because of the difficulty in demonstrating 
their presence. This requires a slight amount of plasmolysis, but not 
enough to rupture the connexions. When the mother-cells are very young, 
before the growth period begins, they are so small that no plasmolysis 
occurs, and the presence of connexions cannot therefore be observed in 
ordinarily fixed material at this stage of development. It seems most 
probable, however, that these connexions are formed by openings left 
in the cell-plate when it was originally laid down. These cytoplasmic 
connexions must form an important avenue of interchange between adjacent 
mother-cells. It is probable that during this process of extrusion the 
nucleus merely utilizes the connexions which happen to occupy the 
appropriate position. 
If there are several of these openings near together, extrusion may take 
place through all of them. There may be a number of connexions on the 
