ZIZYPHUS PARRYI. 31 
ZIZYPHUS PARRYI. (Plate 5 and fig. 15.) 
Zizyphus occurs sparingly on the river-bottoms or elsewhere where the 
water conditions are fairly good. It is a grayish-colored (due to hairy 
covering) spiny shrub from 1.5 to 3 m. high and bears during favorable 
seasons a considerable leaf-surface. As is the case with the most of the 
desert perennials, the leaves fall away with the advent of dry conditions and 
leave the shrub bristling with spines in a condition very much like the 
ordinary condition of Kwéberlinia emoryt. 
Fic. 15.—Zizyphus parryi: Section of stem 3 mm. in diameter, 
to show distribution of chlorophyll. cz. 4.,cortical chlorophyll 
band; 4. 4., hard bast; cam., cambium. 
The young stem of Zizyphus shows the customary divisions into cortex, 
wood, and pith, of which the latter is especially abundant. The main 
divisions of the cortex are the epidermis with its rather-heavy cuticle, a 
chlorophyll band beneath the epidermis, a hard-bast ring which is discon- 
tinuous, and the ground tissue between it and the cambium. 
The distribution of the chlorophyll is very much as in other plants. The 
outer cortical parenchyma, most of the inner cortical parenchyma, the 
medullary rays, and the outer pith-cells contain chlorophyll. The outer 
chlorophyll band, which is interrupted at frequent and fairly regular inter- 
vals by masses of collenchyma, has a palisade structure, at least in the 
outer part, of short cells very like the cells in the leaf. The inner chloren- 
chyma cells are cuboid. The parenchyma and the collenchyma between 
the chlorophyll band and the groups of hard bast deeper in the cortex con- 
tain chlorophyll. The medullary rays of the cortex are also chlorophyll- 
bearing. The rays either end in the groups of hard bast or pass outward 
