PLANT ECOLOGY AND FLORISTICS OF SALTON SINK. 101 



THE TREES OF SALTON SINK. 



In the preceding pages the trees have been referred to only incidentally, the purpose 

 being to reserve further remarks concerning them for a few separate paragraphs. They 

 fall into three classes: those which grow only in wet soil, those which tolerate both wet 

 and superficially dry soils, and those confined to arid soils. 



The first class comprises the palm (Washingtonia filifera), the black willow (Salix 

 nigra), and the delta Cottonwood (Populus macdougalii). There are but few indigenous 

 palms in the Sink — the two at Dos Palmas and a group of half a dozen in the alkaline flats 

 near Mecca. There are said to be some others in the flats, but they were not found by the 

 writer. They are abundant along the bases of the mountains northeast of Indio, and in 

 various places in the canons, but beyond the borders of the Sink. 



The desert palm has a columnar trunk 50 feet or more in height and 6 to 8 feet in circum- 

 ference, surmounted by a crown of large leaves, whose fan-shaped blades are borne on long 

 and stout petioles. Their functional life is about a year, and as they die they continually 

 add to the mass of deflexed dead leaves hanging beneath the living ones. The palm flowers 

 in May and June, each tree producing five or six large branched panicles of chartaceous 

 blossoms. The fruit, a thin edible flesh surrounding a large bony seed, ripens in early fall. 



As it grows in the Sink, Salix nigra has a rough-barked trunk seldom exceeding 6 feet 

 in height. An unusually large specimen measured 82 inches in circumference at 3 feet 

 from the ground. The black willow fruits in May or June, and so abundantly that often 

 the branches are white with the silky coma of the seeds as it bursts from the opening 

 capsules. Large mature trees are usually found as solitary specimens, or in small groups, 

 but there are often small thickets of pole-saplings along the rivers. 



The delta Cottonwood has a clear trunk of 15 feet to the branches. One near Mecca 

 was 86 inches in circumference at 3 feet from the ground, but larger ones were seen. None 

 comparable in size to that attained by the common California Cottonwood (Populus fre- 

 montii) are to be found in the Sink or have been seen in the bottom lands of the lower 

 Colorado River. Both this and the black willow require abundant and easily reached 

 water, but neither will endure a large excess of alkali. 



The two species of Prosopis constitute the second class. Both are tolerant of widely 

 varying edaphic conditions. They reach their best development in the drier and less 

 alkaline parts of the flats about Indio and Mecca, but are also found in those which have 

 large alkaline and water content. Towards the Mexican boundary, and still more beyond 

 it, they cover large tracts of alluvium in open orchard forest. The occurrence of P. glandu- 

 losa buried in dunes and mounds, at either margin of the Sink, has been more than once 

 alluded to. P. pubescens and more rarely P. glandulosa are sometimes seen as solitary 

 specimens in dry detrital soils; but they probably never grow where permanent moisture 

 is beyond the reach of their deeply penetrating roots. Indeed, the desert inhabitants 

 hold them to indicate the presence of water at no great depth. 



It is seldom that a mesquite (P. glandulosa) can be found with a single trunk more 

 than a foot to the point of branching. One at Mecca had a trunk 18 inches to the branches 

 and 42 inches in circumference; another, at Indio, had a trunk 30 inches high and 78 inches 

 in circumference. Usually a number of large stems start from the surface, broadly spread- 

 ing and becoming much deflexed, so that it is difficult to penetrate the outer circle of 

 branchlets. The tree flowers in early spring, and in the fall the clusters of thick pods, 

 5 to 8 inches in length, ripen and eventually fall to the ground. The crop is usually abun- 

 dant, but there are occasional failures. 



The screwbean is a smaller, less branched, and more erect and slender tree, rarely 

 exceeding 15 feet in height, but usually with a single trunk. Two specimens at Mecca 

 had trunks respectively 38 and 42 inches in height and 20 and 24 inches in circumference. 



