316 CALIFORNIA ACADEMY OF SCIENCES. [Proc. .v> Skr. 



distances. The delicate radiating lines connecting them are 

 clearly evident (fig. 57), and in these the cell-plates are 

 soon visible, and the nuclei are thus enclosed in polygonal 

 areas which become cells by this transformation of the cell- 

 plates into cellulose membranes (fig. 58). The cells at the 

 apex of the sac are quite irregular in form and completely 

 surround the embryo (fig. 37). At the sides of the sac these 

 cells seen from the surface are often regularly hexagonal. 

 The endosperm-cells at the apex have much denser con- 

 tents than those at the sides, which are almost transparent. 

 Figure 56 illustrates the way in which the development of 

 the endosperm proceeds centripetally. This section is a 

 nearly median one and shows how the nuclear divisions are 

 mainly in a plane parallel to the periphery of the sac. The 

 first-formed endosperm-cells are at first open on their inner 

 face, and when the nucleus divides a division-wall is found 

 closing up the outer cell, but leaving the inner one also 

 open. This continues, one layer of new cells after another 

 being added to the endosperm, until finally the whole upper 

 part of the sac is filled up, but the lower portion remains 

 open in the center up to a late enlarged period. Free 

 nuclei can always be seen in this open part of the sac, lying 

 in the layer of protoplasm covering the free walls of the 

 inner endosperm-cells. 



The endosperm-nuclei become a good deal enlarged 

 before the division-walls are formed, and these enlarged 

 nuclei generally show several nucleoli. The younger stages 

 have only a single nucleolus and the outline of the nucleus 

 is round and oval. As they increase in size, it was found 

 that the nucleolus became elongated and constricted (fig. 

 58), finally resulting in a division into two, generally 

 unequal, portions. This is probably repeated in the case 

 of those which have more than two nucleoli. Each nucle- 

 olus is surrounded by a clear area, while the rest of the 

 nucleus presents a granular appearance. As the nucleus 

 itself becomes more or less distorted in outline with the 

 division of the nucleolus, and often appears lobed, it was at 

 first supposed that we had to do with a case of nuclear 



