240 FTichols, A morphological study of Juniperus communis var. depressct. 
Fig. 61. Spore mother cell undergoing heterotypic division. X 800. 
Fig. 62. Longitudinal section through base of nucellus to show tapetum. 
X 392. 
Fig. 63. Daughter nuclei of heterotypic division. Reconstructed from 
two adjoining sections. X 800. (In this figure the megaspore mother cell is 
drawn on a larger scale.) 
Figs. 64, 65, 66. Various phases in the homotypic division of the mega¬ 
spore mother cell. X 800. 
Fig. 67. Group of three mother cells which have undergone division. 
Reconstructed from two adjoining sections. X 800. 
Figs. 68, 69. Functional megaspore sliortly before the first free nuclear 
division. The sliriveled remains of the non-functional cells are still visible. 
x 800. 
Fig. 70. Embryo sac after first free nuclear division. X 800; 
Plate XIV. 
Development of prothallium and formation of arehegonia. 
Fig. 71. Section of embryo sac containing sixteen free nuclei. X 800. 
Fig. 72. Radial section of embryo sac shortly before the formation of 
protliallial tissue, showing nuclei dividing simultaneously. X 340. 
Fig. 73. Section of megaspore membrane at the time of fertilization. 
X 800. 
Fig. 74. Prothallium shortly after the development of primary walls. 
Radial section. X 340. 
Fig. 75. The same. Surface view of inner, open ends of cells. X 340. 
Fig. 76. The same. Optical section parallel to spore membrane. X 340. 
Fig. 77. Radial section through prothallium at a later stage of de¬ 
velopment. X 340. 
Fig. 78. Tip of prothallium after the formation of arehegonia. X 80. 
Plate XV. 
Fig. 79. Mature central cell nucleus in tip of arcliegonium. X 340. 
Figs. 80—85. Successive stages in division of central cell nucleus to 
form ventral canal nucleus and egg nucleus. X 340. 
Figs. 86, 87. Egg nuclei and unusually well developed ventral canal 
nuclei shortly after their formation. X 340. 
Plate XVI. 
Figs. 88, 89. Ventral canal nuclei atthetips of arehegonia in which the 
egg has beeil fertilized. X 306. 
Fig. 90. Two nuclei resulting from. the mitotic division of the ventral 
canal nucleus. X 306. 
Fig. 91. Tip of prothallium shortly before fertilization showing group 
of arehegonia and pollen tube in archegonium chamber. X 104. 
Fig. 92. Mature egg nucleus. X 340. 
Fig. 93. Rucleolus of central cell nucleus. X 1280. 
Fig. 94. Tip of a pollen tube which contained one small and two large 
male cells. One of the latter has already entered an archegonium. X 306. 
