74 BOTANICAL FEATURES OF NORTH AMERICAN DESERTS. 
rosettes when nearly mature and after cutting away the tips of the leaves 
bake the central stem and attached leaf-bases for the sugary substances 
to be obtained, making what is known as mescal. The mescal-pits used 
a decade ago are numerous in the foothills of the mountains in this region, 
and even yet one may occasionally surprise an Indian feasting upon this 
prized delicacy. 
The yuccas and the sotols (Dasylirion) form a great central stem 
several feet in height with a heavy plume of leaves which may live to a 
great age. The inflorescence in these plants arises some distance from 
the apex of the stem and the flowering period does not terminate the 
existence of the individual asin the agave. The yuccas occur at a higher 
level than Tucson, while the sotol (Dasylirion wheelert) inhabits the 
rocky canyon slopes a thousand feet above, although stragglers are found 
nearer (plate 58). The southern slopes of the Catalinas and of other 
mountains in this region is also the habitat of the small agave (A. schottiz), 
which has stiff spiny upright leaves less than a foot in length, and as the 
planis grow thickly together an ascent among them is tediousand painful. 
With this species is to be found also the rarer A. treleasw, which so far 
seems to be found only on the slopes of the Santa Catalina Mountains. 
The yellow of the hillsides of the early part of the year due to Encelia 
has hardly faded when equally conspicuous clumps of RKiddellia begin to 
show at the same level, and the globular clusters of this plant endure for 
many weeks. During their display the bright yellow bloom of the par- 
kinsonias contributes to the yellow color-note. Parkinsonia microphylla 
(palo verde) and P. torreyana are true desert trees, having very minute 
leaf-blades which are cast at any time when the water-supply fails, and 
which use the green layers of the bark instead when the leaves are lacking 
(plate 59). 
Two other pod-forming groups of trees are also active at this time, the 
acacias and the mesquites. Of acacia there are two species, one with white 
and the other yellow flowers, which are sweet-scented and are borne in 
globular clusters on the small trees. Mesquite attains its greatest growth 
on the alluvial bottom-lands, and it is capable of sending long roots to 
great depths in search of water. The delicate green of its leaves is an 
especial feature in contrast with the gray and yellow of the arid landscape. 
In April and May small racemes of whitish flowers are followed by the pods 
and bean-like seeds, which are such an important feature in the life of 
many animals and of the Indian (plate 60). 
The hackberry (Celtis) and Lycium are also to be mentioned among the 
woody plants which bloom and mature their fruit during this season. Of 
the plants which grow from seed every year none are more striking than 
the thistle-poppy (Argemone), which affects sandy slopes and washes, 
the glistening spiny stems and leaves being of a grayish-green, a true 
desert color. A large number of buds are developed and one or more are 
