PAYSON—MONOGRAPH OF THE GENUS LESQUERELLA 115 
carpa, or L. auriculata, may be traced the manner of evolution 
from a simple hair to a few-rayed, stellate hair. That the simple 
or few-branched hair is the more primitive form there can scarcely 
be a doubt, and if there were it would be dispelled by correlating 
the relative increase in number of rays with the advance of other 
specializations. In the great majority of species the stellae 
are nearly symmetrieal and the rays are rather conspicuously 
forked above the base. In the more primitive forms the rays 
are few and distinct and as progression occurs they become 
more numerous and are often more or less regularly or irregularly 
united. Frequently the stellae are conspicuously granular, 
particularly near the center, with accumulations of lime, but the 
degree to which these granules are developed and the exact num- 
ber of the rays vary greatly within the species. 
There are two deviations from the normal type of trichome 
structure. The first of these concerns L. densiflora and L. Engel- 
mannii, but is more easily observed in the former than in the latter. 
Its peculiarity consists in a deeper U-shaped notch on one side that 
renders the stellae somewhat unsymmetrical. This notch is 
quite universally directed toward the base of the stem or the 
leaf which would suggest that the stimulus for its development 
had some connection with gravitational force. Curiously enough 
even on horizontal stems this notch parallels the axis of the 
stem and so in this case the notch is at right angles to the pull 
of gravity. However, this would be explained if these hori- 
zontal stems were erect during the period of trichome formation. 
L. Engelmannii possesses this characteristic to a less striking de- 
gree, as has already been remarked, and this is due in large part to 
the more numerous rays which in a measure “crowd out" the 
notch. These two species, with L. ovalifolia, form an interesting 
series of gradually increasing specialization. In L. ovalifolia 
the stellae are quite symmetrical and the notch has disappeared. 
The rays are also decidedly more numerous than in L. Engel- 
mannii. The second departure from the usual type of stellate 
trichome unites the six members of the argyraea group. Here 
the rays are described as unbranched, and if they are forked, 
the forking occurs so near the center of the stars as to render it 
inconspicuous. The resulting characteristic form is easily dis- 
tinguished from the more common type by referring to the dia- 
