32 THE SERI INDIANS |eth.ann.17 



iu the driest areas. Nearly all of the plants have roots of exceptional 

 length. ;ind are protected from evaporation by a glazed epidermis and 

 from animal enemies by thorns or by offensive odors and flavors; while 

 most of the trees and shrubs are practically leafless except during the 

 humid seasons. Grasses are not characteristic, and there is no sward, 

 even in oases; but certain grasses grow in the shadow of the arbores- 

 cent tufts and in the fields of the farmer ants, or spring up in scatteied 

 blades over the moister i^ortious of the surface. The arborescent veg- 

 etation represents two characteristic types, viz, (1) trees and shrubs 

 allied to those of humid lands, but modified to fit arid conditions; and 

 (ii) distinctive forms, evidently born of desert conditions and not adapted 

 to a humid habitat, tliis type comprising the cacti and related forms, 

 as well as fornas apparently intermediate between the cacti and normal 

 arborescent type. The various plants of the district, including those 

 of the distinctive types, are communal or commensal, both among 

 themselves and with animals, to a remarkable degree; for their com- 

 mon strife against the hard physical environment lias forced them into 

 cooperation for mutual support. The tufts or clusters in which the 

 vegetation is arranged express the solidarity of life iu the province; 

 commonly each cluster is a vital colony, made up of plants of various 

 genera and orders, and forming a home for animal life also of ditterent 

 genera and orders; and, although measurably inimical, these various 

 orgaiiisins are so far interdependent that none could survive without 

 the cooperation of the otliers.' 



In Seriland proper, as in other parts of the Sonoran iirovince, a pre- 

 vailing tree is tlie mesquite {I'rosopis jidijiora); on the alluvial fan of 

 Rio Sonora it grows in remarkable luxuriance, forming (with a few 

 other trees) a practically continuous forest 20 to 40 feet in height, the 

 gnarled trunks sometimes reaching a diameter of 2 or 3 feet; over the 

 Rio Bacnache fan and much of the remaining plain surface it forms the 

 dominant tree in the scattered vital colonies; and here and there it 

 pushes well into the canyon gorges. The roots of the mesquite are of 

 great length, and are said to penetrate to water-bearing strata at depths 

 of 50 to 7.5 feet; its fruit consists of small hard beans embedded in slen- 

 der woody pods. Associated with the mesquite iu most stations are the 

 still more scraggy and thorny cat-claw (Acacio f/reygii) and ironwood 

 (OIneya tesofa), both also yielding woody beans in limited quantity. 

 Similarly associated, especially iu the drier tracts, and characteristically 

 abundant over the plains portions of Isla Tiburon, are the paloverdes 

 (Parkinsoiiia torreyana, etc), forming scraggy, wide-branching, green- 

 bark trees 5 to 15 feet high, and commonly 3 to 10 inches in diameter 

 of trunk. Over the mountain sides, especially of Sierra Seri and Sierra 

 Kunkaak. grow sparsely the only straight-trunk trees of the region, 

 rooted in the rocks to the average number of a few score to the square 



■The vital characteristics of the regiou have been described iit suiue detail in The Beginning of 

 Agriculture, American Anthropologist, vol. VIII, 1805, pp. 350-375 ; The Beginning of Zooculliire, Amer- 

 ican Ant hroi>o]ogi8t, vol. X, 1897. pp. 215-230; and Expedition to Seriland, Science, vol. in, 1896, pp. 493-505. 



