50 BOTANY OF THE DEATH VALLEY EXPEDITION. 



Teiradymia glabrata.— The loaves are of two kinds, those borne on the shoots of 

 the season, and those home, fasciculate at the nodes, on one-year-old stems. The 

 former are filiform-linear, longer than the others, acute at the apex, and l.ear an 

 arachnoid pubescence. The others are shorter, obtuse, glabrous, and undoubtedly 

 early deciduous. 



Teiradymia spinosa.—The stems are covered with a close dense tomentnra, and the 

 pedicels and involucral bracts with arachnoid pubescence, while the primary leaves, 

 which are transformed to slender spines, are at first arachnoid-pubescent, then gla- 

 brate, and the axillary-fasciculate leaves are glabrous or at first arachnoid. 



Thamnosma montana.— The stem has a large pith and a thin layer of wood. The 

 bark remains green, without thickening, for sometimes three or four years. Its 

 surface is devoid of pubescence, but is roughened with blunt elevations, each con- 

 taining an imbedded gland. The small leaves are linear-oblanceolate, glahrous, 

 sparingly impressed-glandular, and very early deciduous. 



Keturning now to a topical review of the characters presented, I 

 may remark, first, the small yearly growth of brandies, both in length 

 and thickness. This is such a common character of the shrubs previ- 

 ously enumerated, that it is scarcely necessary to mention particular 

 cases. It is rare for a branch of a desert shrub to grow more than 10 

 cm. in a single season, and most of them grow far less. This character 

 is to be considered a necessary outcome of reduced potential growth 

 rather than a modification to lessen evaporation, yet it reciprocally pro- 

 duces that very effect. 



Size, form, and thickness of leaves are points in which a striking com- 

 munity of modification is exhibited. Of the forty one shrubs examined, 

 only four, Aster moharensis, Atriplex hymenelytra, and the two Eucelia; 

 have leaves whose single surface-area exceeds 1 sq. cm. Most plants 

 of Aster mohavensis have leaves of inueh smaller area, and it is probable 

 that all of them lose the power of transpiration early in summer. The 

 other three plants have a specially modified protective epidermal cover- 

 ing, which compensates largely for their size. In the direction ot 

 minuteness in functionating leaves there is no limit, for in Cereus and 

 Echinocactus they arc entirely wanting, while in Ephedra they are rep- 

 resented by scales devoid of chlorophyll and so constructed as to pre- 

 clude the possibility of transpiration. In such cases all the trans- 

 piration is carried on by the stem. 



The form and thickness of the leaves of these shrubs arc direct 

 modifications for reducing the evaporating surface. Eight species have, 

 as stated above, nontranspiring leaves, eighteen have entire leaves 

 varying from filiform to linear-oblong, nine are entire and obovate to 

 orbicular, while only seven have the ordinary form of an ovate, acuminate, 

 toothed, or lobed blade. In this statement leaflets of compound leaves, 

 such as those of Cassia and Balea, are treated as single leaves. The 

 tendency toward thickening of the assimilative leaves in this series of 

 plants is conspicuous, and the resulting leaf is commonly of a fleshy 

 texture. Kot a single species bore a really thin leaf. These facts in- 

 dicate a strong tendency toward simplicity and compactness of form. ,, 



The early falling of leaves in desert shrubs is a matter that has at- 

 tracted little attention. In Cassia armata, Lyeium andersonii, Salazaria 



