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SCIENCE. 



[Vol. XX. No. 515 



SCIENCE: 



Published by N. D. C. HODGES, 871 Broadway, New York. 



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SKETCH OF THE FLORA OF DEA.TH VALLEY, CALI- 

 FORNIA.' 



BY FREDERICK VERNON COVrLLE, WASHINGTON, D.C. 



Since Death Valley, as shown by the published records of the 

 Weather Bureau,^ is the hottest and drvest arpa known in the 

 United States, and probably in the world, and since the observa- 

 tions of the Death Valley Expedition showed that the>e extreme 

 climatic conditions are reflected in its vegetable life, a de.icription 

 of this flora has an interest even greater than that incited by the 

 average desert vegetation. 



One not familiar with the Mohave and Colorado deserts must 

 imagine broad stretches of treeless plains, out of which rise 

 abrupt mountains, not covered with trees but exhibiting naked 

 faces of rugged rocks with no covering of soil or lichens to con- 

 ceal even their coloration. In the northern portion of the Mohave 

 Desert region, in which Death Valley lies, the mountain ranges 

 are closer together and the plain is cut up into narrow deep val- 

 leys trending in a general north and south direction. The deepest 

 of these is Death Valley, its length about 175 miles, and its great- 

 est breadth from peak to peak about 20 miles. The lowest por- 

 tion of the valley is a moist plain about 40 miles long by 2 to 6 

 miles broad, gleaming with salt and alkali. Between this and 

 the mountain faces are sloping gravelly mesas, at some parts of 

 the valley 6 miles broad, at other points entirely absent. The 

 mountains themselves are abrupt and naked, the Funeral Moun- 

 tains on the east rising 7,000 feet, the Panamints on the west 

 almost 11,000. Upon the crest of the Panamint range is an ever- 

 green forest of pines and junipers. 



The salt-flat in the bottom of the valley is quite devoid of vege- 

 tation, not because the moisture in the soil is too scant, but be- 

 cause it is so saturated with salt and alkaline compounds that no 

 plant can live upon it. 



The mesa bears a growth of scattered shrubs not sufficient, 

 even at a distance, to conceal the ground between them. No 

 larger plant is to be seen except at certain points where, along 

 the line between the mesa and the salt-flat, the sub-soil is sufii- 

 ciently moist to support the mesquite. This is a low, almost 

 shrab-like, tree which commonly attains a height of 10 to 15 feet. 

 This characteristic then, the absence of trees, may be taken as 

 the most conspicuous feature of the Death Valley vegetation, as 

 it is of the desert in general. 



> In January, 1891, an expedition was sent out by the U. S. Department of 

 Agriculture to explore the region of Death Valley, California, and to make a 

 biological survey of it. About nine months were spent In the field, and the 

 report, now nearly completed, will soon be published by the department. 

 The general botanical features ol the region, a full discussion of which will 

 constitute a part of the final report, are here described by the botanist of the 

 expedition. 



' U. S. Department of Agriculture, Weather Bureau Bulletin No. 1, Notes 

 on the Climate and Meteorology of Death Valley, California, by Mark W. Har- 

 rington. Washington, 1892. 



The mesas bear, besides the shrubs, a large number of berba- 

 ceo is plants which, although in late summer and in winter 

 dead and barely noticeable, in the spring months of a rainy year 

 come to be in some places really conspicuous. One of the desert 

 sunflowers {Encelia eriocephala) was at one point so abundant 

 that it even made the mesa appear yellow, at a distance, over an 

 area many rods in extent. The general impression, however, of 

 the traveller who is not a botanist is that the vegetation of the val- 

 ley consists of clumps of mesquite set here and there along the edge 

 of the salt flat, and a few scattered greasewood and creosote bushes 

 on the mesa. 



Not all parts of the mesa are, however, supplied with even so 

 much plant life. At the mouth of Furnace Creek Canon is a broad 

 slope composed of mixed gravel, sand, and clay, a matrix capable, 

 in some parts of the desert, of supporting a varied flora; but here 

 for hundreds of yards is seen no plant whatever except one of the 

 smallest greasewoods (Atriplex hymenelytra), its individuals grow- 

 ing far apart and attaining the height of barely a foot. 



In still other portions of the mesa occurred a phenomenon 

 which, if it is here interpreted rightly, is the best index that we 

 have of the intense heat of this region. The higher portions of 

 the mesa are cut up by the dry channels of the streams that fol- 

 low mountain cloudbursts. Between these channels, which are 

 callerl sometimes arroyas but oftener washes, are broad blocks of 

 the mesa, whose surface has lain undisturbed for undoubtedly 

 many thousands of years. The surface of the soil is covered 

 closely with a layer of small, flat, water-worn stones which have 

 accumulated on the top of the ground by the gradual washing 

 out of their original clavey matrix. The erosion of the soil has 

 undoubtedly heen brought about by the slow agency of direct 

 ruinfall. The upper surfaces of the stones have a dark brown^ 

 almost black, color, and the dull lustre of a hard-burned brick. 

 The coloration of these stones is ascribed to binoxide of manganese, 

 produced by oxidation due to intense light acting during long 

 periods of time'. These so-called sunburned areas in Death Val- 

 ley bear no vegetation whatever. Even the two desert annuals, 

 Chorizantlie rigicla and Chamactis altenuata, which grow at other 

 points in the hottest spots, are here wanting. The soil, a firm 

 clayey one, is good, and the surface receives just as much rainfall 

 as other parts of the valley. The phenomenon is explained by no 

 hypothesis except that of intense heat, and a consideration of the 

 evidence, in the absence of direct experiment, indicates that such 

 a cause may be quite sufficient. 



Experiments by Sachs upon active protoplasm have shown that 

 when subjected to a temperature of 50° C. (138° F.) it ceases to. 

 carry on its functions, disintegration sets in, and death follows. 

 But a plant may be situated in an atmosphere whose temperature 

 is higher than this without itself attaining so great a heat; for 

 two causes tend to reduce its temperature, the non-conductive 

 nature of the tissues themselves, and the evaporation that char- 

 acterizes transpiration. Yet even these sources of protection may 

 be overridden by a still higher temperature. The well-known 

 retention of vitality in the case of the spores of certain fungi after 

 exposure to a temperature of even 212° F. does not indicate that 

 a desert plant can endure a similar degree, for the protoplasm of 

 the fungus spore is not in a state of activity, but that o' a germi- 

 nating or growing plant is. 



The Weather Bureau tables, in the bulletin cited above, show 

 five records of a temperature of 123° F. This is the temperature 

 of air sheltered from the effects of radiation. The temperature of 

 air exposed to ordinary conditions of radiation must be somewhat 

 higher than this, and the temperature of gravel pebbles on the 

 surface of the ground still higher; but, according to the principles 

 of molecular physics, the black stones that have been described 

 should reach a degree of heat decidedly greater than either of the 

 other bodies. It is confidently believed that a temperature of 

 from 140° to 150° F. is frequently attained under these conditions, 

 and in such a temperature a growing plant would undoubtedly 

 perish from heat. 



That the flora of the valley may be more readily considered, all 

 the species observed there have been arranged in groups. A re- 

 view of these groups suggests some of the leading characteristics 

 3 See Annual Report of the Wheeler Survey for 1876, pp. 178, 179. 



