314 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Skk- 



meantime become completely filled with the endosperm. 

 The full-grown embryo (fig. 52) is a spindle-shaped body, 

 of which the cotyledon constitutes much the greater portion. 

 The outer edges of the sheath at the base of the cotyledon 

 overlap so as to completely conceal the stem-apex and sec- 

 ond leaf (fig. 54). 



A longitudinal section through the base of the full-grown 

 embryo (fig. 53) shows that the root is very broad and 

 short. Occupying its axis is the conical plerome which in 

 section shows about six rows of cells; this ends at the basal 

 wall whose limits are still discernible. No single initial cell 

 could be made out at the apex of the plerome, nor could 

 any absolute regularity in the segmentation of the terminal 

 cells be recognized. Connected with the main plerome- 

 strand are smaller branches extending into the young leaves, 

 but, as already stated, none is given off to the stem. Be- 

 tween the plerome of the root and the epidermis there are 

 five or six layers of cells. 



The origin of the other tissues of the root can be traced 

 back to the central group of cells lying next the apex of the 

 plerome and derived from the central cells of the second 

 segment of the embryo. There are probably four of these 

 initial cells, and two can usually be seen in longitudinal sec- 

 tions. Periclinal segments are cut off from those which add 

 to the root-cap, and lateral segments are also formed which, 

 dividing again, form the initials for the dermatogen and 

 periblem. The primary root of the embryo of Sfiarganium 

 therefore conforms closely to the type described by De Bary 

 (1884), as found most commonly in Monocotyledons. The 

 root-cap is well developed in the older embryo and has the 

 form of a biconvex lens, as the central part of the root-apex 

 is strongly concave. 



A noticeable difference between the embryo of Spargan- 

 ium and that of most other aquatic Monocotyledons hith- 

 erto examined, e. g. Alisma, JVaias, Lilcea, etc., is the ab- 

 sence of the larger vesicular suspensor cell, so conspicuous 

 in those forms. This cell is evidently of great importance 

 in these plants, and directly concerned with the food supply 



