648 Part IV, Chapter 5. 
Three species of Beaucarnea (among them D. oedıpus) known locally as 
“sotol” have the bases of their stems swollen to the thickness of seven or 
eight, feet with a height not more than two or three Times this measurement. 
On the hills, a gray, dwarf vegetation is encountered, consisting of Zchzno- 
cactus ingens associated with Yucca aloifolia, Dasylirion acrotrichum (?), com- 
posite herbs and discontinuous grassy clumps. In other associations in the 
vicinity occur, according to KARSTEN '), Agave horrida, Echinocactus ingens 
(see Fig. 30 at p. 644) and on a leafless shrub grows 72landsia recurvata. 
Another association consists of Cereus Pecten aboriginum (see Fig. 9, pP. 297), 
Fig. 31. Cereus (Myrtillocactus) geometrizans Matt. (Garambullo). Chihuahuan Desert Region, Mexico. 
Prosopis juliflora and Cereus (Pachycereus) marginatus, while on the limestone 
plateau at Hacienda Carnero, Tehuacan, grow together in association Kchino- 
cactus robustus, Mamillaria mutabilis and Tradescantia navicularis. Else- 
where, the gray vegetal covering of the soil is found to consist of species of 
Agave, Dasylirion, earth inhabiting bromeliads, species of Sedum and Eche- 
veria, thorn-bearing shrubs, such as, Mimosa, Cassia, many compositous 
plants and Zphedra. The grassy covering is thin and sparse, beset with 
species of cactaceous plants. 3 
1) SCHIMPER, A. F. W.: Pflanzengeographie auf physiologischer Grundlage. 1898. 678—679; 
KARSTEN, G. and STAHL, E.: Mexikanische Kakteen-, Agave- und Bromeliaceen-Vegetation. Vege- 
tationsbilder Heft 8. 
