PRATT: CYCLOLOMA ATRIPLICIFOLIUM. 89 



of the primary vascular bundles and of the woody cylinder of the 

 stem follow. 



The epidermis consists of one layer of cellulose-walled cells, the 

 lumina of which appear rectangular or circular in cross section. 

 The cell walls show more thickening down through the regions II 

 and III (figs. 8, a, and 9, a); and the lumina of the cells in region 

 IV (fig. 10, a) have become very small because of this thickening. 

 The external wall, which is thicker than the other walls, does not 

 have a cutinized layer in young and medium-sized stems, but 

 develops a cuticle, which, although a very thin film in region I 

 (fig. 7), is more prominent in regions II and III (figs. 8 and 9). 

 The gi'eatest thickness of the cuticle is only .002 mm., attained in 

 region III (fig. 9). The cuticle stains a bright reddish-orange 

 color in chloroiodide of zinc, and bright red in Sudan III and 

 alcannin. 



The epidermal cells of the ribs of the stem are elongated longi- 

 tudinally (figs. 12 and 13) approximately four times their tangen- 

 tial dimensions (fig. 9, a), and show a slightly greater dimension 

 tangentially than radially (fig. 9, a). The epidermal cells other 

 than those on the ribs of the stem are slightly elongated longitu- 

 dinally or have relatively equal longitudinal (figs. 14 and 15) and 

 tangential (fig. 9, a) dimensions, and have greater tangential than 

 radial dimensions (fig. 9, a). The inner tangential wall of the 

 epidermal cells joins up in a somewhat irregular line with the 

 primary cortex cells (fig. 10, a). In surface view Salsoli kali also 

 has lengthened epidermal cells of the ribs and isodiametric epider- 

 mal cells between the ribs, according to Solereder ('08). 



The epidermis of very young stems is thick.y covered with 

 clothing and glandular hairs (figs. 16 and 17). As would be ex- 

 pected, the hairs are not so numerous in region II as in region I; 

 still fewer hairs are found on region III, and usually only basal 

 portions of hairs remain in region IV. The hairs of the stem are 

 discussed later with the hairs of the leaf. 



The stomata of the epidermis of the stem are like those de- 

 scribed for the leaf in this article, and are almost as numerous, 

 there being 117 per sq. mm. (Figs. 12 and 14.) 



Subepidermal gi'oups of collenchyma (fig. 9, h) projecting as 

 ribs; groups of parenchyma (fig. 9, c) intervening between the 

 ribs; also parenchyma (fig. 9, i) between the collenchyma groups 

 and the starch sheath; and the starch sheath (fig. 9, d), make up 

 the primary cortex. 



