Plate XI 



PLATE XI 



Figure 67. — Cross section through young tlieca 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. X 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. X 60. 



Figure 69.— Cross section through .slightly older theca of a flower 

 0.25 mm. long ; showing division initiating development of 

 sejDtum, and also formation of the primary parietal la3'er. X 600. 



Figure 70. — Section of flowers from which figure 69 is taken. 

 X marks the region in figure 69. X 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 laj'ers, in places, and .septum. X 600. 



Figure 72. — Section of flowers from which figure 71 is taken. 

 X marks the regrion shown in fipure 71. X 60. 



Figure 73. — Cross section through theca of a flower measuring 

 0.33 mm. in length; showing spoi^ogenous cells in two sacs of 

 theca, two parietal layers, and septum. X 400. 



Figure 74. — Cross section through one of the sacs of a theca of 

 a flower measuring about 0.5 mm. in length. Parietal la^-ers 

 often three in number. X 400. 



Figure 75.^Group of cells from cross section of pollen-sac; show- 

 ing pollen mother-cells surrounded by the still intact tapetum. 

 X GOO. 



Figure 76. — Portion of section through older pollen-sac ; showing 

 pollen mother-cells and dissolution of tapetal cells. X 600. 



Figure 77. —Section of megasporangium showing two megaspore 

 mother-cells and one parietal layer. X 375. 



Figure 78. — Section of megasporangium showing four daughter- 

 cells resulting from a double mother-cell, and also two parietal 

 layers. X 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. X 375. 



