20 BOTANICAL FEATURES OF NORTH AMERICAN DESERTS. 
several malpighiaceous and other woody vines which associate themselves 
with clumps of the trees and shrubs. Among these vines are the sarama- 
traka (Cereus striata), with branching stems o.2 to 0.3 inch in diameter, 
which reach a length of 4 feet or more, growing through and reclining 
upon the bushes; and the guarequi (/bervillea sonore), a cucurbitaceous 
tendril-bearing plant whose inordinately thickened root and stem base lies 
gray and half exposed upon the ground beneath some trellising shrub 
(plate 10). These tuberous formations may be seen during the dry 
season lying about wholly unanchored, as the slender roots dry up with 
the close of the vegetative season, which lasts but a few weeks. In 
February, 1902, some of these tubers were taken to the New York Botan- 
ical Garden, and a large specimen not treated in any way was placed in 
a museum case, where it has since remained. Annually, at a time fairly 
coincident with the natural vegetative season in its native habitat, the 
major vegetative points awaken and send up a few thin shoots which 
reach a length of about 2 feet only, since they do not obtain sunlight. 
After a period of a few weeks they die down again and the material in 
them retreats to the tuber, to await another season. Seven periods of 
activity have thus been displayed by this specimen with no apparent 
change in its structure or size. It does not seem unreasonable to sup- 
pose, therefore, that the guarequi is a storage structure of such great 
efficiency that water and other material sufficient to meet the needs of 
the plant for a quarter of a century are held in reserve in its reservoirs. 
The guarequi is reputed locally to be very poisonous, but repeated 
tests by Dr. William J. Gies and Miss Julia Emerson, with living material, 
hot and cold water extracts, and alcoholic extracts fail to produce any 
results with the various animals used as test objects. It is quite 
possible, however, that the living vines or the fruits might yield sub- 
stances upon which the prevailing opinion is based. 
Westward from Torres the vegetation of the desert continues with 
little change until the line of hills is approached beyond which the coun- 
try drops down to a plain still lower and nearer the waters of the Gulf. 
Here are the tree ocotillo (Fouquierta), a brasil (He@matoxylon), torote 
prieto (Terebinthus), the tree morning-glory (Ipomea arborescens), and the 
beautiful palo lisso (Acacia willardiana). This last is a small tree with 
the whitest of bark peeling off in tissue-paper films, a slender trunk with 
graceful spreading branches, and curious compound leaves made up mostly 
of flat green rachis with an extremely small leaflet area toward the sum- 
mit. The morning-glory is a tree 20 to 30 feet high, with smooth chalky 
gray trunk and branches, leafless at this season throughout, its large white 
flowers opening one by one on the ends of the naked branches. From its 
white bark the tree is sometimes known as palo blanco, and from the gum 
or resin which exudes from incisions made in it for the purpose and which 
is used as incense in religious ceremonies it 1s called also palo santo. 
