Nuevo Laredo, Tamaulipas, Monterrey, Nuevo Leon, Mexico to Valle, San Luis Potosi, Mexico June 27, 1946 covered with low scrub, and from the road no free growth could be observed on the east-facing slope. At this point the roadside vegetation is rather heavy, identifiable plants including two yuccas, mesquite, desert manwood, and tuna cactus. Cuesta de Monnuligue is a long, fairly steep grade approximately 25 mi. north of Monterrey, Nuevo Leon. The mountains over which the road leads are sedimentary in nature. The vegetation is xerophytic scrub. Altimeter reading at the crest of the cuesta was 2100 feet. The mountains a few miles south of Monterrey come nearly to the edge of the road. The range west of the road is the main Sierra Madre Oriental, and is very high and sheer, sparsely vegetated on the east-facing slopes. The range on the east of the road is a spur of the main moun- tain mass, and although quite steep, is not so high nor rugged as the main range. The spur range, on the west-facing slope, is uniformly clothed with a low, scrubby vegetation. The crest of the east-facing slope of the main Sierra Madre Oriental seems to support a fairly heavy free growth. These moun- tains are topped with clouds, and apparently the mountain tops get a high precipitation. Here the forests. Altimeter reading 5 mi. south of Monterrey = 1850 feet. Arroyo Cristatines is