240 Nichols, A morphological study of Juniperus communis var. depressä. 



Fig. 61. Spore mother cell undergoiug lieterotypic division. X 800. 



Fig. 62. Longitudinal section through base of nucellus to show tapetum. 

 X 392. 



Fig. 63. Daughter nuclei of lieterotypic 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 shortly before the first free nuclear 

 division. The shriveled 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 archegonia. 



Fig. 71. Section of embryo sac containing sixteen free nuclei. X 800. 



Fig. 72. Radial section of embryo sac shortly before the formation of 

 prothallial tissue, showing nuclei dividing simultaneously. X 640. 



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 640. 



Fig. 75. The same. Surface view of inner, open ends of cells. X 640. 



Fig. 76. The same. Optical section parallel to spore membrane. X 640. 



Fig. 77. Radial section through prothallium at a later stage of de- 

 velopment. X 640. 



Fior. 78. Tip of prothallium after the formation of archegonia. X 80. 



Plate XV. 



Fig. 79. Mature central cell nucleus in tip of archegonium. X 640. 



Figs. 80 — 85. Successive stages in division of central cell nucleus to 

 form ventral canal nucleus and egg nucleus. X 640. 



Figs. 86, 87. Egg nuclei and unusually well developed ventral canal 

 nuclei shortly after their formation. X 640. 



Plate XVI. 



Figs. 88, 89. Ventral canal nuclei atthetips of archegonia in which the 

 egg has been 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 archegonia and pollen tube in archegonium Chamber. X 104. 



Fig. 92. Mature egg nucleus. X 640. 



Fig. 93. ISTucleolus 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. 



