8 TOPOGRAPHY OF CHLOROPHYLL APPARATUS IN DESERT PLANTS. 
chlorenchyma of the leaf was observed also in AKvrameria canescens, where 
the cortical chlorophyll band is likewise palisade. 
CELTIS PALLIDA. (Plate 2, B, and figs. 2 and 3.) 
The specimen of Ce/tis which was chosen for study is growing in the 
arroyo below and to the east of the Laboratory building. A branch about 
2m. in length was selected and sections made at the following distances 
from the tip: 6, 21, 34, 49, 64, 79, 144, and 178 cm. The parts of the 
branch where the sec- 
tions were made had 
the following diame- 
ters: 2, 3.5,4, 4.5, 6, 
8, 8.5 mm. and 1 and. 
1.6 cm., respectively. 
A section of a branch 
2mm.in diameter and 
6 cm. from the tip 
shows the following 
general structural re- 
lations : 
Cortex: There are 
several well - defined 
cortical divisions. An 
epidermis with a thin 
outer wall and a sub- 
epidermal tissue about 
three cells in thick- 
ness bound the stem. 
Within this lies a 
oa te oo Cane, 
eee chlorophyll band 
Fic. 2.—Celtis pallida: A, section of branch 2 mm.in diam- which is also about 
eter; B, section of branch 3.5 mm. im diameter. . ‘ 
oes oe three cells in thick- 
ness. A discontinuous ring of hard bast is situated within the chlorophyll 
band. Betwéen the hard bast and the cambium is the region of the inner 
cortical parenchyma. 
Woody cylinder: The wood is composed very largely of wood fibers with 
a noticeably small amount of wood parenchyma. The pith is well marked 
but does not need further mention in this connection. . 
Chlorophyll occurs in the outer cortical parenchyma, in much of the par- 
enchyma which lies between the hard bast and the wood, in the medullary 
rays, both of wood and of cortex, and in the outer cells of the pith. 
* The term chlorophyll band as used in this paper refers to that portion of the cortical 
parenchyma that lies between the epidermis and the ring of mechanical tissue which is 
about midway between the epidermis and the cambium. It is the largest and the most 
enduring chlorophyll tissue in the stem. 
