1897.] Vegetable Physiology. 439 
giving usually a gray color to the physiognomy. The hairs must be 
dead and filled with air. 6. Anatomical structure. The epidermis 
may be cutinized, or encrusted with various substances; the stomata 
may be sunken or otherwise protected. The contrivances for this 
purpose are legion. 7. The author calls attention to the frequent pres- 
ence of etherial oils in xerophytes, and, though the use is not clear, 
suggests that the leaf becomes coated with a layer of the vapor of this 
volatile oil ; and, since this layer is much less diathermous than air, 
the evaporation is lessened. 
Under adaptations for absorbing water may be mentioned certain 
glandular hairs of desert plants and air-roots of epiphytic orchids. 
Some kinds of glandular hairs secrete hygroscopic salts, such as calcium 
chloride, which readily absorb water. “ Volkens thinks that the plants 
take up water in this way. Marloth, however, regards this salt coat 
only as a covering to hinder transpiration, and even thinks that the 
plants thus free themselves from a part of the salts taken up.” 
Under storage of water we have various kinds of water tissue, succu- 
lent plants with sap which does not readily part with its water, and 
fleshy underground parts. 
An outline of the xerophite classes may be of interest. 
“A. Rock vegetation, that of the subglacial and temperate regions : 
that of dry tropics. 
“B. Subglacial vegetation upon loose. earth. Stony plains sparsely 
beset with plants, due often to lack of warmth rather than lack of 
moisture ; moss heaths; lichen heaths. 
“C. Dwarf-shrub heaths (mostly Ericacec). 
“D. Sand vegetation, Strand flora, discussed more at length under 
Halophytes ; vegetation of shifting dunes; vegetation of permanent 
dunes ; sandy scrubs and timbered barrens. 
“E. Tropical deserts. 
“F. Xerophilous, herbaceous vegetation. Steppes and prairies; . 
savannahs, 
“G. Stony heaths (Felsenheiden) such as the Asiatic steppes cov- 
ered with thorny shrubs. 
“H. Xerophilous scrubs (Gebiische). In arctic and temperate 
regions; in Alpine regions; tropical thorn-, palm-, fern-, bamboo- 
scrubs, ete. 
“I. Xerophilous forests. Evergreen conifers; deciduous conifers ; 
xerophilous, deciduous forests; leafless forests (Casuarina).” 
The other three primary divisions are discussed in a similarly 
thorough manner. Swamp plants frequently possess xerophilous char- 
