98 THE SALTON SEA. 



dunes of drifted sand; but in the very compact soil they are not found. The inference is 

 easy that they largely owe their extended range to the ability of their roots to go deep for 

 water in soils that permit penetration. 



A certain endemic perennial herb, Astragalus limatus, which is scattered all over the 

 Sink, at once impresses one as often out of place in its surroundings. It belongs to a genus 

 well represented in the arid west, where numerous species exhibit the reduced foliage, the 

 protective indument, or the limited growing period, which adapts them to their environ- 

 ment. This species has numerous and fairly broad leaflets, which are but slightly thick- 

 ened; only the growing apex is protected by a sparse pubescence, and while the lower 

 leaves die those above continue green and growing throughout the year. It is, in short, a 

 plant of more mesophytic than xerophytic aspect. Probably an examination of its root- 

 system would explain the apparently incongruous conditions under which it often grows. 



AGE OF THE XEROPHYTIC TREES AND SHRUBS. 



The student of the arid mesas of the Sink is at once impressed by the apparent great 

 age of most of the ligneous vegetation. It is true that this appearance may be aided by 

 the unsymmetrical forms of many of the trees, by the sparseness or absence of foliage, 

 and by the grayness of the shrubs. No investigations directed to this subject have been 

 made in the Sink, but this aspect of age is characteristic of the sylva of the deserts, only 

 accentuated here in its most arid part. Shreve 1 has recently made determinations of the 

 age of 14G specimens of Parkinsonia micro phylla, a leguminous desert tree growing near 

 Tucson. He found the age of 50 of them to be 200 years and upwards, the oldest exceed- 

 ing 400 years. Only 10 were of the comparatively youthful age of 75 years. It is probable, 

 therefore, that the aged appearance of the desert trees and shrubs is not altogether decep- 

 tive. The proportion of very old trees may be expected to be greater in the Sink than at 

 Tucson, where the aridity is much less. It is greatly to be desired that extended investi- 

 gations of this nature should be made on the Salton trees. 



ABSENCE OF SEEDLINGS. 



The absence of seedlings and of juvenile and adolescent individuals is a topic of interest, 

 in connection with the question of age. During the course of more than a month devoted, 

 at several periods of the year, to a study of the flora of the Sink, the writer did not see a 

 single seedling or the withered remains of one, save of annuals, in any of its arid portions. 

 This deficiency is not due to a lack of seed production; on the contrary the vegetation is 

 exceptionally fertile. Atriplex canescens is literally weighed down with its heavy fruitage. 

 The mesquite produces abundant crops, and the screwbeaii is little less prolific. Beneath 

 Parosela schottii the ripened pods lie thick. In short, all the perennials, from the trees to 

 the radiate Chamsesyces that he prostrate on the soil, are most prolific in the production 

 of seeds, and the annuals are equally fertile. 



Instructive experiments carried on by Dr. MacDougal, to ascertain the readiness of 

 germination and the duration of the viability of the seeds of the desert plants, are detailed 

 in another section of this report. Incidental facts shed some light upon these points. 

 Cercidium torreyanum has been extensively planted as a street tree in the town of 

 Brawley, in Imperial Valley. The trees have now reached the fruiting age, and prove 

 objectionable because of the great number of seedlings which spring up in the lawns and 

 streets. In the same valley, while annuals are far from common, there seems to be an 

 accumulation of their seeds in the dry earth, for no sooner is a place well wetted than there 

 springs up an abundance of certain species. 



It is altogether probable that the absence of seedlings is due, not to any cause inherent 

 in the seeds themselves, but to the want of proper conditions for their germination. These 



1 Shreve, F. Establishment behavior of the palo verde. Plant World, xiv, p. 293, 1911. 



