llS THE PLANT WORLD. 



places, both at an altitude of between 5000 and 6000 feet, 

 the species was recorded as occupying a southerly aspect. 



In covering the interval between the Chiricahua Moun- 

 tains and Tucson, it was seen but once on each of two routes, 

 viz.: clinging to gravelly banks of arroyos, between Mescal 

 and Pantano, on the Southern Pacific Railroad, and filling the 

 Interstices between blocks of bedrock sloping toward Nugent's 

 Pass where this breaks through the Caliuro Mountains into 

 the San Pedro Valley. II occurs on similar habitats in Sabiiio 

 and Ventano Canyons in the Santa Catalina Range, and 

 one mile up the latter canyon it has been noted growing on 

 a steep north slope, under rocks, at probably 3500 feet. In 

 the Tucson mountains it has been met once on Quijotoa 

 road, keeping close under a wash bank, facing north, and 

 again in the narrow, well-protected defile on the north side of 

 Mount Tucson, filling spaces between large rocks; neither 

 place has much over 3000 feet elevation. On Tumamoc Hill 

 it grows as considerable colonies only in the best protected 

 places of steep, northerly aspect, between the contours of 

 2500 and 3100 feet. It has not been found on the south 

 side of the hill, and if present at all, must be exceedingly 

 rare. 



In following a third route eastward between Tucson 



and the Chiricahuas, the species in question was first seen on 

 the pebbly bank of an arroyo where first the surface begins 

 to rise perceptibly toward the Santa Rita Mountains. The 

 altitude here is not far from 4000 feet, and the Lippia still 

 grew on a bank facing northward. It was not encountered 

 again until reaching the southern foothills of the Mustang 

 Mountains, where it bordered sparingly a gully at 5000 feet, 

 apparently not particular as to aspect. In the San Pedro 

 V^alley it made its first appearance four miles east of Fair- 

 bank, fringing the steep sides of a gravel run, and a second, 

 six miles east, on the river bluffs, composed of similar coarse 

 material. Again, it occurred on the peculiar erosion area 

 some two or three miles west of Tombstone, clinging in 



