SUMMARY OF RESULTS. 41 
SUMMARY. 
The leading results of this study may be summarized as follows: 
1. Young stems of desert perennials contain chlorophyll in most of the 
parenchyma, both of cortex and of woody cylinder. The most important 
chlorophyll-bearing tissue appears in transverse sections of the stem as a 
band in the outer part of the cortex. 
2. The epidermis of branches of Parkinsonia 1 cm. in diameter may 
contain chlorophyll. 
3. Chlorophyll is present in the phelloderm of the following species: 
Celtis pallida, Condalia spathulaca, Olneva tesota. 
4. There is no chlorophyll in the woody evlinder of -4ster shinosus or 
Baccharis emorvi. 
5. The woody cylinder in young stems of Ephedra antisyphilitica and of 
Olneya tesota do not contain chlorophyll; in older stems the woody cylinder 
of both is chlorophyllaceous. 
6. The chlorophyll band in the stems of Cereus, Fouquieria, Avameria, 
Parkinsonia, and probably also in Zizyphus, persists throughout the life of 
the member bearing it. In most plants it is ultimately cut off through 
the formation of cork. 
7. As regards foliar habits the plants studied may be classified into two 
groups, which, however, are not always well marked. In one class leaves 
are either rudimentary or wanting; in the other, leaves are present at least 
during the favorable seasons, /. e., when the water-supply is adequate to 
their needs. 
8. The differences in leaf-covering are accompanied by fairly consistent 
morphological differences, as follows: The plants with reduced leaf-surface, 
or with no leaves, have palisade chlorenchyma in the cortex; the chloro- 
phyll band, at least in young stems, lies near the surface; the tissues exte- 
rior to the band in young and generally in‘old leaves do not exhibit pro- 
tective devices. Plants with a more pronounced leaf-surface, on the other 
hand, have a spongy chlorenchyma in the cortex; it is usually more deeply 
placed; and the exterior tissue usually has some protective arrangements, 
as pigmented cells or a hairy covering. 
9. The greatest depth at which functional chlorophyll was found ranged 
from 0.38 mm. in Kewéerlinia spinosa to 6.6 mm. in Cereus giganteus. This 
is from 0.5 to 165 times deeper than the greatest depth of chlorophyll in 
ordinary leaves. 
10. The depth of penetration is probably limited by the air-supply rather 
than the supply of light. 
11. The chlorophyll band of the stem constitutes practically the sole 
engine for carbon assimilation in Aster spinosus, Baccharis emoryvi, Cereus 
giganteus, Keberlinia spinosa, Krameria canescens, and the most important 
