208 
Transactions of the Royal Society of South Africa. 
cortex and pericycle are of a simple type, each consisting of a much elongated 
endodermal cell showing the usual cuticular band (figs. 17, 18). The single 
stele is placed somewhat obliquely in the middle of the air space. The one- 
layered pericycle is usually separated from the xylem by one or more layers 
of thin-walled phloem cells. Occasionally a xylem tracheide is found to 
abut directly upon the endodermis. The stele is usually somewhat elliptical 
in form, with two protoxylem groups. 
Stomata are confined to the margin (fig. 19, a) and the aligular surface 
of the leaf. They occur along the vein, often extending beyond its termina- 
tion, and may appear also on the two wings. With the exception of the 
c 
e 
Fig. 19. 
cotyledons, a conspicuous leaf-base is present below the insertion of the 
ligule, and here a definite group of stomata is always found (fig. 19, b). Up 
to twenty stomata have been counted in this region. 
The guard cells are placed parallel to the leaf-margin (fig. 19, c). Only 
one instance of a transverse position was noted (fig. 19, d). As many as 
seven epidermal cells may abut upon a single stoma. The number of 
stomata present may vary within wide limits. When very numerous, 
adjacent stomata such as those shown in fig. 19, e, may occur. 
As mentioned above, the leaf-base, except in the cotyledons, is well 
developed. It contains a mass of aerenchyma roofed over by an epidermis 
which is perforated by numerous stomata (figs. 19, b, 20, 21). Sykes and 
Stiles (15) describe and figure a similar air cavity in the projecting base of 
the sporophyll of certain species of Selaginella, and compare it with the 
mucilage cavity of Lycopodium and the parichnos of fossil genera. It is 
