be around a farmhouse in the United States. Ir 



i addition to 



yielding fruits the stems make admirable hedges 



or barriers, 



although when planting for this purpose alone soi 



ne species of 



Cereus are generally used. 





The evaporation in the Tehuacan region must 



be much in 



excess of the precipitation, yet it was noticeable tha 



t the various 



species of Opuntia were to be seen growing on dirt r 



oofs of adobe 



dwellings, on stone walls, and even in crevices of br 



ick and stone 



high up on cathedrals and other tall buildings. The 



; air tempera- 



tures are favorable to such exposure but the protective and 

 regulatory devices of such plants must be of the highest kind. 



No desert has yet been visited by the writer in which the 

 storage function is so highly developed and exhibited by so 

 many genera of plants as in the arid region of Tehuacan. In 

 addition to the cacti, euphorbias, agaves, and related forms, the 

 tree morning glory {Jpomoea sp.) has a soft thick trunk into which! 

 a knife may be easily thrust to the hilt and is chiefly a storage 

 organ. Three species of Beaucarnea, relatives of the yucca, 

 known locally as " sotol " have the bases of the trunks swollen 

 to a thickness of seven or eight feet with a height not more than 

 two or three times this measurement, by the formation of an 

 immense mass of spongy tissue with great capacity for retaining 

 water. Like many other plants showing similar adaptions these 

 trees sit directly on the surface and may be easily pushed over, 

 especially after dead. 



On the jungly slopes we encountered Rhus potentillaefolia, 

 and found its poisonous effect on the skin as virulent as that of 



Here as elsewhere in Mexico it was found that the broad leaves 

 of the agave are sliced and the dried plates used in covering the 

 huts and enramadas of the peons and Indians. 



we proceeded southward by rail to Oaxaca de Juarez, where we 

 were so fortunate as to encounter Prof. Conzatti, of the Escuela 

 Normal, who has long been known as an ardent student of the 

 flora of this region. From him we obtained much valuable inform 

 mation not only as to distribution and general features of the 



