178 MORPHOLOGY OF ANGIOSPERMS 



is formed, so that there are three superposed chambers, and only 

 in the one nearest the micropyle does division proceed. As a 

 result, a dense, small-celled tissue is formed near the embryo 

 (Fig. 80). In Datura laevis (Guignard 48 ), after the first divi- 

 sion into two chambers (Fig. 74), transverse walls are formed 

 in each, resulting in four superposed chambers in which further 

 division proceeds in various planes. 



V There are also cases in which each division of an endosperm 

 nucleus is accompanied by a transverse wall across the sac, as 

 in Sar codes (Oliver 11 ), in which the mature sac is several- 

 chambered by a series of delicate transverse walls. The same is 

 doubtless true of Pistia, whose narrow sag contains a row of 

 broad discoid endosperm-cells that lie like transverse chambers. 

 One of the most exceptional cases of wall-formation, however^ 

 is that of Peperomia pellucida (Johnson 31 ), in which the first 

 division of the very large primary endosperm nucleus, formed 

 by the fusion of eight nuclei, is followed by a wall from the 

 fertilized egg to the base of the sac, further divisions following 

 until the sac is packed with forty or more endosperm-cells. In 

 a recent study of Heckeria also, one of the Piperaceae, the 

 same investigator 55 has found the same general condition as in 

 Peperomia, in that the endosperm is " cellular " from the first, 

 filling the sac before the egg divides. It is worthy of note that 

 the endosperm of Piper (Johnson 55 ), on the other hand, begins 

 with free nuclear division. It is evident from these differences 

 in closely related genera, also noted by Hofmeister 2 and Hegel- 

 maier, 8 that methods of endosperm formation can not indicate 

 relationship. 



The mature and permanent endosperm is a tissue with no 

 intercellular spaces, w;hose cells are either thin-w r alled, form- 

 ing an endosperm of delicate texture, or thick-walled, resulting 

 in a horny endosperm, as in palms, umbellifers, etc. In case the 

 thickening of the walls becomes excessive, the endosperm is 

 stony, as in Phytelephas, the palm whose seeds furnish the 

 so-called " vegetable ivory." 



The endosperm has sometimes been observed to continue its 

 growth after it has filled the sac. Hofmeister describes the en- 

 dosperm of Crinum capense and some other Amaryllidaceae as 

 bursting the seed-coats, and even the ovary wall, the cells devel- 

 oping chlorophyll, and the tissue remaining succulent and form- 



