STERLING: KRAMERIA CANESCENS GRAY. 865 
But the dense covering of thick-walled trichomes on its sur- 
face provide an excellent means of protection against evapora- 
_ tion. The trichomes are one-celled, with walls strongly cutin- 
ized on the lower portions, and are but weakly, or not at all, 
cutinized on the upper portions. They vary in length from 
150 to 600 microns and average 850 on a sq. mm. (h, fig. 16, 
plate IV). 
Stomata, which stand at right angles to the long axis of the 
stem and lie in the same plane with the epidermal cells, appear 
to be without any of the special protective devices found in 
desert plants, and are protected only by the numerous closely 
appressed trichomes (s, fig. 16, plate IV). The stomata are 
uniformly distributed and average 98 on a sq. mm. The cells 
of the epidermis contain chloroplasts and tannin and have a 
brownish-red color. 
The primary cortex and pericycle are not sharply differen- 
tiated, but in the region of the line d, fig. 3, plate II, there are 
numerous parenchyma cells filled with starch. The location of 
these cells just outside of a zone of tissue containing many bast 
fibers would indicate that they form the inner boundary of the 
primary cortex. The primary cortex is made up of a compact 
palisade and isodiametric or radially elongated parenchyma 
cells (fig. 15, plate IV). The palisade seldom contains more 
than one row of cells, which are closely fitted together, and 
have relatively small intercellular spaces between them. Radi- 
ally, they measure 30 to 48 mm. in diameter and contain an 
average of 120 chloroplasts (cl, fig. 17, plate 1V). The chloro- 
plasts are biconvex and disc-shaped, 4 to 5 microns in diameter 
and 1 to 1.75 microns in thickness. The rest of the primary 
cortex is made up on thin-walled parenchyma cells, most of 
which contain chloroplasts, although many are almost com- 
pletely filled by large rosette-aggregate crystals of calcium 
oxalate, while others filled with starch grains are not uncom- 
mon. Radially they measure from 25 to 45 microns. 
Surrounded by the primary cortex is a pericycle consisting 
of thin-walled parenchyma cells, and angular, rather strongly 
lignified bast fibers (fig. 6, plate Il). The long, slender bast 
fibers occur either singly or in groups, and by means of their 
long, tapering ends are spliced together, forming a tissue well 
suited for strengthening. They have a few very small straight 
pits. In length they vary from 850 to 2050 microns and in 
