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1907] COKER— DEVELOPMENT OF SEED IN PONTEDERIACEAE 295 



which still occupy their little pocket. The origin of this lower tissue 

 has not been determined in all stages for Heteranthera, but from its 

 development in Pontederia there is no doubt that it arises from the 

 division of the lower of the two nuclei produced by the first division 

 of the definitive endosperm nucleus. A later stage of this lower endo- 

 sperm is shown in fig, lo. The section shows five cells below the 

 diaphragm in addition to the antipodals.- It will be seen that the 

 cells below are larger than those above the partition. As this tissue 

 has been studied most carefully in Pontederia, I will not go into detail 

 here in regard to it, as it seems the same in both cases. 



The structure of the nearly mature seed of Heteranthera is of 

 sufficient interest to warrant some description. The axial embryo 

 extends nearly the whole length of the seed, and is surrounded by a 

 large-celled endosperm, which, except in its immediate neighborhood, 

 is densely packed with starch. In figs, ii and 12 are shown longitudi- 

 nal and cross-sections of the seed coats and superficial endosperm. 

 The nucellus is entirely destroyed except for the scarcely recognizable 

 micro pylar cap, and the aleuron layer of the endosperm lies in immedi- 

 ate contact with a heavy cellulose membrane secreted by the inner 

 integument. The inner integument (11) is considerably crushed 

 and its cells are so densely filled with deeply staining material that 

 their outlines are not recognizable except in unusually favorable 

 conditions. Beyond the inner integument is a still heavier cellulose 

 membrane, represented by a white line in the figures. This mem- 

 brane seems to be secreted by the cells of the outer integument, which 

 remains permanently two layers of cells in thickness. The outer 

 layer changes very little in appearance during the development of the 

 seed, remaining thin walled and boxlike, with the long axis immlng 

 parallel to the longitudinal axis of the seed. The cells of the inner 

 layer, on the contrary, undergo great changes. They become much 

 elongated, perpendicular to the long axis of the seed, and flattened in 

 the contrary direction. The partitions parallel to the long axis of 

 the cells are much higher at their ends than in the center, and their 

 outer edges dip inward in a regular curve {fig- 12). As the cells of 

 the outer layer follow this curve, the result is that the surface of the 

 seed becomes channelled and ridged in a longitudinal direction. A 

 longitudinal section of the seed taken near the top of a ridge would 



