Gates.—Pollen Formation in Oenothera gigas . 929 
and cell-plates are again being formed on these spindles. In Fig. 71 the 
same stage is to be seen, but no wall was formed after the first division. 
It is, of course, often difficult to determine just what stage is represented 
in a given mitosis, for the appearances are very different from those of 
ordinary pollen formation, and frequently can only be identified by the 
number and condition of the chromosomes. 
Plate LXIX, Figs. 72-75 are homotypic telophase groups more highly 
magnified. Fig. 72 shows the chromosomes when they have just reached the 
pole of the homotypic spindle. Figs. 73-75 are slightly later, after the 
nuclear membrane has been formed. These nuclei are uncut and show all the 
chromosomes, fourteen in the first two cases and fifteen in the third. Thus one 
chromosome occasionally finds its way to the wrong pole, as I have shown 
in other forms of Oenothera , and such irregularities occur also in normal 
development in O. gigas , as pointed out previously in this paper. 
In Plate LXX, Fig. 76, an evident cleavage of the cytoplasm of the 
mother-cell followed the heterotypic mitosis, and one of the daughter nuclei 
has divided again, this being followed by the beginning of a cleavage of the 
cytoplasm. Fig. 77 is a mother-cell in which there have been evident 
irregularities, and scattered spindle fibres appear in the cell. Pig. 78 
represents two mother-cells in which there have been abortive attempts at 
cell-wall formation following division of the nucleus. In Fig. 79, in the 
upper mother-cell, no walls were formed and nuclei of varying'size lie in the 
cytoplasm, while in the lower mother-cell degeneration of the nuclei is 
evidently taking place. The relationships of the cells, as well as other 
features, make it evident that these all represent mother-cells. The remark¬ 
able variation in the size of these mother-cells has already been mentioned, 
and is very well shown by comparing, e. g., Figs. 79 and 80, which are 
drawn with the same magnification. The latter tiny cell has undergone 
division, but several extra nuclei have been formed in the cytoplasm. In 
Fig. 81 a better attempt was made at completing the tetrad formation in 
the mother-cell, but three small nuclei were formed. 
Figs. 82-84 show other more or less complete attempts to produce 
tetrads. In Fig. 84 apparently only one of the nuclei has undergone the 
homotypic division. Fig. 85 shows a characteristic condition which some¬ 
times occurs after the formation of the tetrad nuclei. The mother-cell 
becomes scanty in cytoplasm, and the nuclei move together and form 
a group in the centre of the cell. 
Of course, in all the mother-cells here described the tetrad of cells 
formed can never function as pollen-grains. All the mother-cells remain 
closely surrounded by the tapetal cells at their sides and by other 
mother-cells at their ends, and there is no tendency for them to 
become free and separate. As already stated, this appears to be due 
to the failure of the surrounding cells of the anther to continue their 
