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EXPLANATION OF PLATES XLI-XLIII 
Fig. 57. Sagittal section of ovary, ovule, and part of subtending bract. Show- 
ing initiation of stigma, stylar canal, parietal cell and definitive archesporial cell. 
X90. 
Fig. 58. Half-grown definitive archesporial cell (embryo sac mother-cell), 
showing character of chromatin net and cytoplasm. X 1,150. 
Fig. 59. Similar section of slightly older embryo sac, showing incipient syn- 
apsis and the initiation of the nuclear disk. X 1,150. 
Fig. 60. Similar section showing nearly complete synapsis. Nuclear disk 
distinct and free from nuclear wall. X 1,1 50. 
Fig. 61. Similar section showing complete synapsis. Nuclear disk distinct. 
Xi,i50- 
Fig. 62. Similar section, showing double and twisted chromatin threads. 
Nuclear disk rough. (Nucleolus in an adjoining section.) Xi,i50. 
Fig. 63. Similar section of slightly later stage, showing formation of chromo- 
somes. Nuclear disk not evident. Xi,i50. 
Fig. 64. Similar section of older embryo sac mother-cell, showing rounded 
chromatin masses in nucleus and large, darkly-staining granules in the cytoplasm, 
though nuclear wall is still intact. Nucleolus and nuclear disk not distinguishable. 
X 1,250. 
Fig. 65. Similar section showing part of spindle of first division of megaspore 
mother-cell. The dark rods near the poles of the spindle are, perhaps, the remains 
of the nuclear disk. X 1,250. 
Fig. 66. Part of a similar section, showing all chromosomes at a later phase 
of the same spindle. X 1,250. 
Fig. 67. Similar section showing the chromatin in the partially organized 
nuclei resulting from the first mitosis in the embryo sac. Cell-plate evident. X i ,250. 
Fig. 68. Approximately longitudinal section of ovule containing binucleate 
embryo sac, showing some remains of the spindle of preceding mitosis. The cell 
plate not distinguishable, probably because of the obliqueness of the section. X350. 
Fig. 69. Longitudinal section of embryo sac showing first 4 nuclei formed, with 
cell-plates. X 1,250. 
Fig. 70. Similar section of an embryo sac, showing 3 megaspore nuclei sur- 
ounded by cytoplasm and separated by call walls, to form megaspores in a tetrad. 
X 1,250. 
