398 Gates and Rees. — Study of Pollen Development in Lactuca. 
PLATE XVIII. 
Figs. 37«-55«. Chromosome bivalents taken from the correspondingly numbered figures in 
Plate XVII, and arranged in rows to show relative lengths and sizes, x 3,000. 
Fig. 55. Metaphase of heterotype division in polar view showing nine bivalents. Note denser 
surrounding layer of cytoplasm, x 3,000. 
Fig. 56. Similar stage in side view. Note again denser area of cytoplasm. x 3,000. 
Fig. 57. Early anaphase. Whole chromosomes beginning to separate from each other, x 3,000. 
Fig. 58. Later anaphase, showing how the bivalents separate. All but the pairs have split 
apart. See p. 386. x 3,000. 
Fig. 59. Later anaphase, cut. x 3,000. 
Fig. 60. Telophase. Nine univalent chromosomes in each daughter nucleus. Most of the 
chromosomes have already split. x 3,000. 
Fig. 61. Abnormal telophase. Nuclei strongly hyperchromatic. Note temporary plate 
forming in spindle, and also chromatic bodies in cytoplasm. x 3,000. 
Fig. 62. Telophase. Chromosomes becoming transformed into a reticulum. Note chromatic |i 
bodies in cytoplasm, x 3,000. 
Fig. 63. Somatic cell from root tip. Anaphase showing eighteen chromosomes varying greatly 
in length in each group. Note vacuolate nature of cytoplasm, x 3,000. 
Fig. 64. Somatic nucleus in prophase from tissue of young bud, showing chromosomes of various 
lengths, x 3,000. 
PLATE XIX. 
Fig. 65. Abnormal pollen mother-cell in heterotypic telophase stage, showing supernumerary 
nuclei, x 3,000. 
Fig. 66. Pollen mother-cell showing tetrad formation. Note invagination of cytoplasm to form i 
the pollen grains, x 3,000. 
Fig. 67. Similar stage to above, but the furrows have progressed farther and they cut across the 
spindle fibres. Fourth grain indicated by dotted lines, x 3,000. 
Fig. 68. Tetrad after pollen grains have separated from each other, but are still enclosed in 
mother-cell. Note heptagonal shape of grains and beginning of thickening of the walls. x 1,500. 
Fig. 69. Abnormal tetrad in later stage, after mother-cell wall has disappeared. Note that 
only three pollen grains are present and central one is binucleate. x 3,000. 
Fig. 70. Pollen grain showing thickenings of the wall, x 3,000. 
Fig. 71. Pollen grain with still thicker wall and ‘frills ’ in process of formation, x 3,000. 
Fig. 72. Portion of loculus with three mature pollen grains. Note sculpturing of grains, and 
plasmodium formed by breaking down of tapetal cells, x 1,500. 
Fig. 73. Small tapetal cell with two nuclei. Pollen mother-cells in diakinesis. x 1,500. 
Fig. 74. Tapetal cell, with two nuclei in synizesis. Mother-cells in early spireme stage. 1 
x 3,000. 
Figs. 75, 77. Binucleate tapetal cells. Mother-cells of loculus in diakinesis. x 1,500. 
Fig. 76. Binucleate tapetal cell on larger scale, both nuclei in prophase stage of second division, 
x 3,000. 
Fig. 78. Single nucleus of binucleate tapetal cell. Note chromatic bodies, x 3,000. 
Fig. 79. Binucleate tapetal cell from end of loculus. Note only two chromatic bodies to each 1 
nucleus, x 1,500. 
Fig. 80. Quadrinucleate tapetal cell from middle of loculus. Note length of cell, x 1,500. 
Fig. 81. Quadrinucleate tapetal cell from end of a loculus. Note shape and compare with 
Fig. 80. The two central nuclei are breaking down. x 1,500. 
Fig. 82. Trinucleate tapetal cell. Two nuclei in synizesis. Central one apparently result 
of fusion of two nuclei each in spireme stage, x 3,000. 
Figs. 83-86. Various stages in degeneration of tapetal cells. Note fragmentation and degenera- 
tion of nuclei and disintegration of cell-walls. Mother-cells of Figs. 83, 85, and 86 in tetrad stage. 
Fig. 84, pollen grains formed, x 1,500. 
