26 BOTANICAL FEATURES OF NORTH AMERICAN DESERTS. 
on adobe and stone walls, and high up among the bricks and stones of 
cathedrals and other tall buildings. Various species of Tzllandsia were 
abundant on Fouquierta sp., shrubs, opuntias, and yuccas. A form 
with broader leaves formed striking tufts on the stems of Cephalo- 
cereus, to which it simply clung, and no evidence could be obtained of 
parasitism. One group was seen in which an opuntia had found lodg- 
ment in the sinus of a trunk of a Yucca valida, forming several internodes, 
making a stem a yard in length, to which there was clinging tufts of a 
filiform T1llandsia. 
While making an examination of these numerous examples of the 
storage function, which appear to be more numerous here than elsewhere, 
one can not escape the suggestion that possibly the high lime content of 
the soil may facilitate it to some extent. 
The Tehuacan region furnishes a fair proportion of spinose shrubs, 
including Fouquieria sp., but outside of the cacti very few with markedly 
reduced leaf surfaces such as exhibited by Parkinsonia, Parosela, Cassia, 
Prosopis, and other leguminous shrubs (plate 20). Of these the sweet 
mesquite, Prosopis dulce, has a pod in which considerable sweetish tissue 
surrounds the hard seeds. Loranths are common and fasten to several 
species, including the harder shrubs as well as the soft I[pom@a. So far 
as could be learned during the brief examination, no species were espe- 
cially protected by poisonous substances except Rhus potentillefolia, which 
grows on western slopes among other shrubs, looking most unlike a 
poison ivy. Not being acquainted with its properties, it was handled 
carelessly, with the result that its dermatitic effects were found to be 
severe and lasting. 
TOMELLIN. 
One day was spent in a portion of the same drainage system with 
Tehuacan at Tomellin, at an elevation of 1,200 feet, which in latitude 
19° N. gives distinctly tropical conditions. Here is perhaps the most 
massive of all cacti, Cereus webert (plate 21), which with its numerous 
thick branches arising from a central stem within a short distance from 
the ground, is found on the hill slopes and valleys. Near it was the much- 
branched slender Escontria chiotilla, while an Echinocactus and a few 
species of Opuntia are found in among the woody shrubs. Leguminous 
trees and shrubs come in to form a greater part of the landscape, showing 
a distinctly tropical influence, and some trees of Juliana of the newly 
erected family of Julianaceze were found near the station. A short 
distance to the southward Puilocereus tetetzo formed great forests on the 
slopes facing the afternoon sun (plate 22). 
