116 ' BOTANICAL GAZETTE [AUGUST 
“Yerba Santa.’’ All the species are essentially Upper Sonoran, 
but range in their zonal distribution from the upper edge of the 
Lower Sonoran to the Transition. 
Propagation may be by seed or, at least in E. californicum, it 
may be by suckers; whole colonies or thickets are often connected 
by lateral roots that lie only three or four inches below the surface 
of the ground. In the xerophytic habitat where these plants 
usually grow, ability to propagate in this manner is an effective 
factor, for seedlings have difficulty withstanding the long dry 
seasons. 
The leaves present striking examples of adaptations to xero- 
phytic conditions, which fall into two categories. One type, 
represented by E. californicum, has the upper surface covered by 
sessile glands that give a smooth varnished appearance, and the 
lower surface conspicuously reticulate-veined with the stomatic 
surface in the sunken meshes clothed more or less densely with a 
short grayish tomentum. The palisade tissue is also prominent, 
comprising several tiers of cells. Other xerophytic adaptations 
in this type are mainly in the reduction of leaf surface; in E. 
californicum, an inhabitant of central and northern California, 
the normal leaf is flat and 10-15 mm. wide, while in E. angusti- 
folium, of the Arizona mountains, where xerophytic conditions are 
more severe, the leaves are revolute and only 2-5 mm. wide. 
In the other foliage type, represented by E. crassifolium, both 
surfaces of the leaves are clothed with thick-walled unicellular 
trichomes that form a dense mat over the entire surfaces. In 
E. tomentosum these trichomes stand out at right angles to the sur- 
face for a short distance, then turn sharply and interlace, forming a 
dense felt just above the surface; by this arrangement a sort of 
‘“‘ramada”’ is produced which shuts off the sun’s rays and the hot 
winds, but allows slow diffusion. The palisade layer is much less 
developed than in the glutinous type, comprising a single tier of 
cells instead of several tiers. The leaves are also broader and never 
revolute. 
It is evident that the members of the genus are adapted to 
xerophytic conditions, and that two diverse methods of meeting 
these conditions have been evolved. That the two types have 
