DESERTS OF THE UNITED STATES AND MEXICO 



697 



carbonate that the tissue was unpleas- 

 antly gritty when chewed, and that its 

 crispness made it difficult to express the 

 juice. 



B. flavescens (see page 700) forms 

 small heads in clusters, while in B. ro- 

 busta colonies 10 or 15 feet across, mak- 

 ing mounds 2 or 3 feet high, include hun- 

 dreds of heads. 



No systematic account of any desert is 

 to be found in which the storage function 

 appears so highly developed and by so 

 many species. Of course, all of the cacti 

 exhibit this feature in a very marked de- 

 gree, and a single plant of Pilocereus 

 fulviceps may retain several hundred gal- 

 lons of water. The large stems of Yucca, 

 which is a prominent member of the flora 

 of the slopes, function to this purpose to 

 some extent, while the fleshy leaves of 

 Agave marmorata and other species, and 

 of Hectia, are essentially storage organs 

 for reserve food and surplus water. Here 

 is also a Buphorbia and a Pedilanthus, 

 with thick upright cylindrical stems, in 

 which the storage function is made more 

 effective by the possession of a thick 

 milky juice. 



The tree morning-glory (Ipoincea) 

 has a soft, thick trunk, into which a knife 

 may be easily thrust to the hilt, the tis- 

 sues being highly charged with water and 

 containing some reserve food material. 



Perhaps of all of the plants which 

 show this capacity, however, Beaucarnea 

 oed-ipus is the most remarkable. This 

 relative of the Yucca, like all plants of 

 this group with narrow leaves, is known 

 as ''sotol," and has the bases of the 

 trunks swollen in adult specimens to a 

 diameter of 7 or 8 feet, the topmost 

 branch not reaching a height of more 

 than 25. This trunk has a truncate base 

 resting almost upon the top of the 

 ground, to which it is attached by a few 

 slender roots. After death, the loss of 

 water reduces the weight of the storage 

 organ so much that a large plant may be 

 easily toppled over as it stands. 



IN the: DE:SERT near MITLA, MEXICO 



As one proceeds to the ancient ruins of 

 Mitla, 36 miles to the southeastward of 



Oaxaca, the aridity increases until in the 

 vicinity of the hacienda of that name ex- 

 treme desert conditions are found. The 

 ancient structures here are indicative of 

 a type of civilization characteristic of 

 the desert, in which cooperation or com- 

 munism was carried to as great lengths 

 as it must have been in the pueblos of 

 the northern deserts in America. 



A short distance to the eastward from 

 Oaxaca lies the village of El Tule, in 

 which grow a large number of cypress 

 trees (Taxodium mucronatum) , one of 

 which stands in the churchyard, and by 

 the claims of local patriotism is the great- 

 est in the world, while for a long time it 

 has been cited as the oldest living. Both 

 of these claims are incapable of actual 

 proof, although the tree has much to jus- 

 tify an interest in it. Six feet from the 

 ground it measures 154 feet in circum- 

 ference, but it may be really two or three 

 individuals fused together, as it divides 

 into that many main branches within 50 

 feet. This tree has been an object of ob- 

 servation for more than two centuries, 

 and on one side is a tablet, partly covered 

 by the growth of the outer layers of the 

 trunk, signed by the great naturalist, 

 Baron von Humboldt, and probably 

 placed there by his direction a century 

 ago. 



From El Tule to Mitla the way passes 

 between fields illustrating methods of ag- 

 riculture in an arid tropical climate. Not 

 the least interesting of these features are 

 the crops of maize of species either prim- 

 itive or directly derived from one of the 

 elementary species of Zea. The high- 

 way, especially where it passes through 

 small villages or near a hacienda, is 

 marked off from the fields and com- 

 pounds by barriers of cacti grown in 

 dense rows. Two or three species of 

 Cereus and several prickly-pears are used 

 for this purpose and also yield a valuable 

 crop of fruit for the owners. 



At Mitla the opportunity was offered 

 for seeing the manufacture of mescal 

 from Agave. Plants of several species 

 and horticultural varieties of Agave, as 

 well as of Yucca and Dasylirion, are up- 

 rooted at a time when the plant is about 



