36 BULLETIN 56, UNITED STATES NATIONAL MUSEUM. 



called cats claws, and claim a place second only to the cacti in popu- 

 lar detestation. Scarcely less familiar and annoying are the mem- 

 bers of the buckthorn family, among them the genera Condalia, 

 Zizyphus, Ceanothus, Colubrina, and Rhamnus. There are also spiny 

 shrubs of the families Oleacem, Saxifragacece, Rosacece, and many 

 others. None are more undisguised and openly aggressive than 

 Kceberlinia, which is necessarily avoided and more easily forgiven 

 than the " ocotillo," which tempts one to grasp a handful of cool 

 leaves in riding past, only to find that every leaf conceals a dagger. 



Ajnong the remarkable plants of the mountains of the Western 

 Desert Tract are woody species of milkweed, of Euphorbia, and of 

 T< rebinthus (Bursera ) . 



Several genera of the family Asteracece are coarse and woody. 

 Aster spinosus grows in masses resembling asparagus in sandy soil 

 beside streams: Baccharis of several species, Hymenoclea, and arrow- 

 wood (Pluchea sericea) form close thickets beside streams or in moist 

 valleys or canyons in the hills, and even the genera Trixis and Senecio 

 in some species develop into large hushes. 



Further details respecting the distribution of the coarser forms of 

 vegetation along the Boundary will be given in the description of 

 the principal collecting stations. A collection of plants aggregating 

 I. us:, numbers and about 10,000 specimens, from the Mexican Boun- 

 dary Line, was made and turned over to Mr. Frederick V. Coville. 

 Botanist of the United States Department of Agriculture, for the pur- 

 pose of being reported upon. As the report has not yet been prepared. 

 a list of the trees is here given, together with such notes regarding 

 their abundance and transverse and vertical distribution as have 

 been retained, some knowledge of the forest trees being essential in 

 order to enable the student to acquire an intelligent understanding 

 of the habitat, distribution, and life history of the different animals. 

 The following list of J.19 species of forest trees found on the Mexican 

 Boundary is not inclusive of those peculiar to the lower Rio Grande 

 Valley: ' 



LIST OF TREES OF THE MEXICAN BOUNDARY LINE. 



PINUS STROBIFORMIS Engelmann. 



MEXICAN WHITE PINE. 



This tree was found at the summits of the main peaks of the San 

 Luis Mountains, south of the Boundary Line (altitude 2,400 meters, 

 or 7,874 feet). It was also found on the Animas Peaks (altitude 

 ii.c,77 meters or 8,783 fret) in New Mexico. In the San Jose Moun- 

 tains (altitude 2,54] meters or 8,337 feet). Sonora, a few trees were 

 found close to the summit of the main peak. It is a common tree 

 on the highest peaks of the Iluachuca Mountains, where it occupies 



