362 BOTANICAL GAZETTE [November 



parenchymatous, and the general structure is shown in figs. 2-6, 8, 



9, 2 9'35- 



The epidermis (ep) consists of large, regular, isodiametric cells 



with large nuclei. That of the cotyledons is abundantly supplied 



with stomata on the exterior surface of the tubular part and a small 



portion of the lobes. No stomata occur on the part of the cotyledons 



remaining in the endosperm, on the interior surface of the cotyledons, 



or on the primordia. The epidermis of the petioles and bases of the 



leaf primordia is covered densely with long, unicellular hairs, with 



well-defined nuclei (figs. 28, 2q). 



The ground tissue is composed of long, regular, prismatic cells, 

 much longer than wide in the cotyledons, but shorter and more isodia- 

 metric in the stem proper (figs. 3, 8). At the lower extremity of the 

 embryo the cells lose their nuclei, become filled with a dense material, 

 and form a hard capping tissue (cp, figs. 3, 28, 29). Distributed 

 irregularly in all parts of the ground tissue are many cells, cavities, 

 and canals filled with mucilage (m, fig. 8; black spots in figs. 28-35). 

 The cavities are found most abundantly in the cotyledons and are 

 formed by the disorganization of several neighboring cells. The 

 canals, which are formed by the disorganization of the cells end to 

 end, forming tubes of limited length, are most abundant in the 

 petioles of both cotyledons and leaves. 



The vascular cylinder is very short, the length being much less than 

 the diameter, and hence it is usually called the vascular plate (vp). 

 It is squarish, one diagonal diameter being approximately at right 

 angles to the inner faces of the cotyledons, and the other parallel 

 with them. The xylem (figs. 32, 33, x), consisting at this stage 

 probably of protoxylem only, is surrounded by a zone of phloem (ph). 

 The xylem is compact and well developed where it borders the phloem, 

 but toward the center it is gradually mixed more and more with 

 pith cells, till in the center the xylem elements lie scattered among the 

 pith cells, these scattered cells being very short and irregular. This 

 condition varies in different specimens, in some the xylem being quite 

 compact to the center, while in others it is entirely wanting in this 

 region (fig. 32). 



The protoxylem groups. — At each corner of the squarish vascular 

 plate there is a group of protoxylem elements (px), which in cross- 



