Pi Acie el 
Figure 67.—Cross section through young theca of a flower 0.2 mm. 
long, the measurement being taken in the direction of the dotted 
line shown in figure 68. Stippled cells represent the arch- 
esporial initials. >< 600. 
Figure 68.—Section of young flowers from which figure 67 is drawn, 
the actual length of each flower being about 0.2 mm. x marks 
the region represented in figure 67. Dotted line shows direction 
for measurement of the length of the flower. >< 60. 
Figure 69.—Cross section through slightly older theca of a flower 
0.25 mm. long; showing division initiating development of 
septum, and also formation of the primary parietal layer. >< 600. 
Figure '70.—Section of flowers from which figure 69 is taken. 
x marks the region in figure 69. >< 60. 
Figure 71.—Cross section through theca of flower measuring about 
0.3 mm. in length; showing sporogenous cells in the two sacs 
of the theca, two parietal layers, in places, and septum. >< 600. 
Figure 72.—Section of flowers from which figure 71 is taken. 
x marks the region shown in figure 71. >< 60. 
Figure 73.—Cross section through theca of a flower measuring 
0.33 mm. in length; showing sporogenous cells in two sacs of 
theca, two parietal layers, and septum. >< 400. 
Figure 74.—Cross section through one of the sacs of a theca of 
a flower measuring about 0.56 mm. in length. Parietal layers 
often three in number. >< 400. 
Figure 75.—Group of cells from cross section of pollen-sac; show- 
ing pollen mother-cells surrounded by the still intact tapetum. 
>< 600. 
Figure 76.—Portion of section through older pollen-sac ; showing 
pollen mother-cells and dissolution of tapetal cells. >< 600. 
Figure 77.—Section of megasporangium showing two megaspore 
mother-cells and one parietal layer. >< 376. 
Figure 78.—Section of megasporangium showing four daughter- 
cells resulting from a double mother-cell, and also two parietal 
layers. >< 400. 
Figure 79.—Section of megasporangium ; showing the four poten- 
tial megaspores, the wall separating the two upper ones being 
approximately parallel to the plane of the paper. The three 
upper cells are all being resorbed. >< 375. 
