BOT.-VOL. I.] CAMPBELL— SPARGANIUM. 313 



Cross-sections of the older embryo are usually more 

 or less oval in outline, the longer axis coinciding with 

 the face of the cotyledon. In sections made just above the 

 basal wall (fig. 47), the first indication of the stem-apex 

 (s/) is evident in a more rapid division in the epidermis 

 where the cells are decidedly narrower. At this time, the 

 section of the plerome shows about nine cells, and the 

 original quadrant divisions are very evident. The stem- 

 apex appears to be the product of one only of the quad- 

 rants, and soon becomes sunk in a depression formed by 

 the excessive growth of the basal cells of the cotyledon 

 immediately adjacent to it (fig. 44). The stem-apex later 

 becomes deeply sunk in the narrow cavity formed by the 

 excessive growth of the base of the cotyledon, and this 

 forms a sheath, such as is so frequently met with among 

 the lower Monocotyledons (figs. 49 and 53). 



The plerome-strand is continued upward into the cotyle- 

 don and downward into the root, but there is no trace of a 

 cauline bundle. The other tissues of the root arise from 

 the cells of the second segment of the embryo. This also 

 divides at first by quadrant walls, and later a central growth 

 of four cells (fig. 44, b) is separated from an outer row of 

 cells. The latter again divides into two by periclinal walls. 

 The initial group of cells, which contributes to the growth 

 of the periblem, dermatogen and calyptrogen, is derived 

 from the four central cells which may be said to constitute 

 the initial for all the tissues of the root except the central 

 plerome-cylinder. 



Before the embryo is mature, the second leaf makes its 

 appearance on the side of the stem opposite the cotyledon. 

 The nearly flat stem-apex develops a protuberance on its 

 outer side, and this quickly assumes the form of a short 

 cylindrical body whose tissues are continuous with those of 

 the stem, except that the plerome-cylinder connects with 

 that of the root. 



The embryo rapidly increases in size as the seed ripens, 

 and finally occupies the whole axial part of the embryo-sac. 

 The space between it and the wall of the sac has in the 



