OP NAIAS GRAMINEAj VAR. DELILEI. 



51 



two layers of cells, which vary in shape according to their 

 position. The portion which covers the ovule consists of 

 elongate cells with truncate ends, and these cells are 

 densely packed with rounded grains of starch very uniform 

 in size. The starch makes its appearance in the later 



Fig. 70. 



Fig. 71. 



Fig. 72. 



stages of the growth of the membrane. The portion which 

 covers the long neck of the flask-shaped body is also 

 mostly composed of long cells ; but the cells which occur 

 on the margins of the stigmatoid divisions of the free ends 

 are only one third the length of the central cells, and their 

 outer ends are somewhat enlarged, so as to make the edge 

 of the stigmatoid divisions minutely papillate, as if to 

 afford better attachment for the grains of pollen (fig. 72). 

 The cells of the base of the neck are much broader than 

 any of those in other parts of the investing membrane, 

 and they are also more loosely aggregated at that point. 

 A central canal runs throughout the narrow portion 



e2 



