940 
Gates.—Pollen Formation in Oenothera gig as. 
PLATE LXX. 
The figures in this plate are all from flowers showing abnormal development, in that the pollen 
mother-cells retain their polyhedral shape. 
Fig. 62. Homotypic prophase, showing spindle formation and the polygonal character of the 
mother-cell, x 2,550. 
Figs. 63 and 64. Heterotypic anaphase, showing the polyhedral shape of the cells and the 
compact, univalent structure of the chromosomes, x 1,875. 
Figs. 65 and 66. Heterotypic telophase, showing an attempt at cell-wall formation. In 
Fig. 66 small extra nuclei appear in the cytoplasm, x 1,875. 
Fig. 67. Heterotypic telophase with extra nuclei in the cytoplasm, x 1,875. 
Fig. 68. Homotypic prophase, showing bivalent chromosomes. The heterotypic mitosis in this 
mother-cell was followed by segmentation of the cytoplasm, x 1,875. 
Fig. 69. Homotypic telophase. One nucleus uncut shows fourteen chromosomes. A cleavage 
of the cytoplasm appears in the line which was the equatorial plane of the heterotypic spindle. 
X 1,875. 
Fig. 70. Homotypic telophase. A complete cell-wall has been formed, following the heterotypic 
division, x 1,125. 
Fig. 71. Same stage as Fig. 70, but no wall formed after the heterotypic mitosis, x 1,125. 
Fig. 76. Late homotypic telophase. Segmentation of the cytoplasm followed the heterotypic 
mitosis, and a cleavage of the cytoplasm is appearing between the two daughter nuclei on the left, 
x 1,125. 
Fig. 77. This mother-cell shows evident irregularities, with extra nuclei, a cleavage of the 
cytoplasm, and scattered spindle fibres, x 1,125. 
Fig. 78. Two mother-cells with abortive attempts at wall formation following division of the 
nucleus, x 1,125. 
Fig. 79. Two mother-cells after irregular reduction divisions. In the upper cell small extra 
nuclei lie in the cytoplasm, while the nuclei of the lower cell are degenerating, x 1,125. 
Fig. 80. A very small mother-cell (cf. Fig. 79), showing irregularities in the chromatin distribu¬ 
tion. x 1,125. 
Fig. 81. A completed tetrad, but three small nuclei formed in the cytoplasm, x 1,125. 
Fig. 82-84. More or less complete attempts to form pollen tetrads. Walls are formed within 
the mother-cell, although the latter remains in contact with adjacent cells. In Fig. 84 apparently 
only one daughter nucleus has undergone the second mitosis. Mother-cell walls very thick, x 1,125. 
Fig. 85. A condition sometimes found after the completion of tetrad formation. The four 
nuclei move together to the centre of the mother-cell, which contains little cytoplasm. In this case 
no walls were formed within the mother-cell, x 1,125. 
