Plate III. 

 All figures refer to Naias flexilis. 



Fig. 54. Two sections of an abnormal embryo-sac, in which apparently 

 the upper archesporial cells were not absorbed as is usually the case, and no 

 definite ^%% apparatus was formed. 



Fig. 55. Lower part of the embryo-sac shown in fig. 54, with six antipodal 

 cells (four only are shown in the section). 



Fig. 56. Section of an ovule which apparently had not been fertilized; 

 the embryo-sac is replaced by a mass of elongated cells; X 200. 



Fig- 57- {« and b) Two sections through a normal embryo-sac, showing 

 fertilization; pt, pollen-tube; o, egg; s, synergidae; k, endosperm nucleus. 

 (c) Lower part of the same embryo-sac, showing two of the antipodals; X 

 450 (about). 



Fig. 58. An abnormal embryo-sac, in which only one cell of the egg 

 apparatus could be certainly distinguished. The end of the pollen-tube was 

 very much enlarged. 



(b) Antipodal region of the same embryo-sac. 



Fig. 59. Endosperm nuclei from an embryo-sac containing an advanced 

 embryo, (a) The single large nucleus above the antipodal cells, which under- 

 goes no division; (b) The smaller secondary nuclei from the upper part of the 

 embryo-sac; X 400. 



Fig. 60. Two sections of the upper part of an embryo-sac, showing the 

 fertilized egg cell, o, and one of the synergidae, s^ which is still intact. 



Fig. 61. (a) Upper part of embryo-sac, with two-celled embryo; X 250. 

 (b\ Endosperm nucleus of the same. 



Figs. 62-66. Successive stages of the developing embryo, in longitudinal 

 section; X 250. stis, primary suspensor cell; k, a secondary endosperm 

 nucleus. 



Fig. 67. Cross-section of an older embryo. 



Fig. 68. Longitudinal section of an embryo, showing the primary 

 segments i, 2, 3. 



Fig. 69. Longitudinal section of an embryo, showing the enlargement at 

 the base of the cotyledon. 



Fig. 70. Two nearly median, longitudinal sections of an older embryo; 

 X 200; 5/, stem-apex; cot, cotyledon; in a, the boundary of the plerome is 

 indicated by a heavy line. 



Fig. 71. Median, longitudinal section of an older embryo. 



Fig. 72. Similar section of a much older one; X 70. 



Fig. 73. Longitudinal section of an embryo from a nearly ripe seed; X 40. 



Fig. 74. Two sections through the apical region of an embryo of the 

 same age as the one shown in fig. 73. 



Figs. 75, 76. Median, longitudinal sections through the root of advanced 

 embryos; />/, plerome; X 200. 



Fig. 77. Root of a full-grown embryo, showing the formation of inter- 

 cellular spaces. 



Figs. 78, 79. Two transverse sections of the root just back of the apex; 

 z/, vessel; en, endodermis; i, intercellular spaces; X 400 



