Histological Studies in the Artemisia Formation 17 
Atriplex cornuta, Plate III, fig. 22. 
This species is a common associate in the drier and slightly 
saline situations. The epidermis is effectively protected by large 
globose epidermal hairs covering the non-cuticularized epidermis. 
These globose hairs or scales are the chief constituent of the so- 
called “mealy” covering so characteristic of the chenopods. The 
hair is usually composed of two cells, one the stalk, or pedicel, 
very short and narrow, the other, the end cell, being the swollen 
globose head which in some may be half as thick as the leaf. The 
chlorenchyma is composed of four rows of prolate palisade cells 
rather loosely aggregated. There are large air chambers imme- 
diately beneath the stomata. There is no indication of mucilag- 
inous storage tissue. The holard here was 8.3 per cent. 
Atriplex canescens. Plate III, fig. 23. 
This is a common shrubby associate of Artemisia. The wood 
is very hard. It is sometimes called “greasewood.”’ The epi- 
dermal walls are not cuticularized, but, as in the above species, 
we have here a dense “meal” of the large globose epidermal hairs 
of the structure described above. The protection is much more 
perfect in this respect than in the above species because the scales 
are more numerous and closely aggregated. The chlorenchyma 
is composed of about four irregular rows of prolate palisade cells 
closely packed together with very narrow intercellular air spaces. 
The development of storage tissue is marked in this species, the 
vascular bundles being always enclosed wholly or in part by a 
sheath of mucilaginous cells. In some cases this sheath is con- 
tinuous around the bundle, but in others it surrounds the bundle 
except at the bottom. In the latter case the sheath fits about the 
bundle like a horseshoe with the open portion toward. the lower 
side of the leaf. In transverse section the cells of the sheath are 
globose or keystone-shaped, and they are about five times as long 
as broad in the direction of the vascular bundle. 
Lupinus ammophilus. Plate IV, fig. 24. 
This leaf lacks a cuticle, and possesses only a few epidermal 
hairs. Many of the epidermal cells are thrown up into short 
papillae. The chlorenchyma is composed of six rows of dense 
427 
