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Carn. Inst. \\' \sii. Pub'n 6

Saguaro or giant cactus ( Cereus. giganteus) near Tucson, Arizona. About 40 feet high. Birds nest in the cavities of the trunk.

Desert Botanical Laboratory

OF THE

Carnegie Institution

FREDERICK VERNON COVILLE

DANIEL TREMBLY MACDOUGAL

WASHINGTON, U. S. A. : PUBLISHED BY THE CARNEGIE INSTITUTION

November, 1903

CARNEGIE INSTITUTION OF WASHINGTON Publication No. 6

Pll» Of

til ■•> EM Piiiriia COMMir,

LAICAtlll, fK

ANNOUNCEMENT.

At the suggestion of Mr. Frederick V, Coville, botanist of the United States Department of Agriculture, the Advisory Committee on Botany of the Carnegie Institution, recommended the establish- ment of a Desert Botanical Laboratory in the arid region of the United States, the purpose of such establishment being to thoroughly study the relation of plants to an arid climate and to substrata of unusual composition. Mr. Coville and Dr. D. T. MacDougal, v^^ho were already well acquainted with the arid regions of the United States, were requested to act as a committee of inquiry on this subject. The results of their inquiry are herewith presented, from which it will ap- pear that a site for a botanical laboratory has been selected near Tuc- son, Arizona. Dr. W. A. Cannon, of the New York Botanical Gar- den, to whom a grant had been made by the Carnegie Institution, in aid of research, has been appointed Resident Investigator in charge of the Laboratory. A suitable structure has been erected, and the investigations commence in the autumn of 1903.

Daniel C. Oilman, President of the Carnegie Institution.

63809

CONTENTS.

PAGE.

Introduction i

Laboratory location trip 2

Itinerary . , 2

Arid region of western Texas 3

Sand dunes of Cliihuahua 4

Tularosa desert . 5

Analyses of sands 8

Tucson as a laboratory site 12

History 14

Nogales . . . 17

Torres 17

Guaymas ,19

Colorado desert 20

Mohave desert 22

Grand Canyon of the Colorado 23

Plant life in North American deserts 23

Meteorology . i$

Tables 25

Discussion 27

Soil 29

Historical 32

Transpiration and temperatures 38

Bibliography 46

ILLUSTRATIONS.

PLATE. FACING PAGE.

I. Giant cactus {Cereus giganteus) near Tucson, Arizona (Frontispiece)

II. Tree yucca ( Yucca radiosa) in the Tularosa desert, New Mexico . 5

III. The White Sands, Tularosa desert 5

IV. Sand column in the White Sands ... 6

V. In the White Sands, Tularosa desert, looking northwest . . 7

VI. Water hole in the White Sands 7

VII. Yucca radiosa growing up through a dune thirty feet high ... 7

VIII. Advancing eastern margin of the White Sands . . 7

IX. Winter vegetation of desert plain at Tucson, Arizona 12

X. Cat's claw tree {Acacia gfeggii) n&ax Tucson 12

XI. Tucson mountain, near Tucson ... 14

XII. Vegetation on Tucson mountain, near Tucson 14

XIII. Looking westward from site of Laboratory 14

XIV. Yucca-like vegetation at Nogales, Arizona 17

XV. Vegetation of the Sonera desert near Torres, Mexico 17

XVI. Guarequi (/^e;'Z'///ea 5o«orae) under bushes, near Torres .... 18

XVII. Tree. ocotiWo {Fouquieria macdougalii) near Torres 18

XVIII. Papago Indian drinking from a cactus {Echinocactus emoryi) . . 19

XIX. Yaki Indian family and house, west of Torres 19

XX. Ollas at a Yaqui Indian house west of Torres 19

XXI. Desert island, Guaymas bay, Mexico ... 20

XXII. Cereus pringlei on above island 20

XXIII. Salt valley, Colorado desert, California 21

XXIV. Salt encrusted ground near Salton, California ... 21

XXV. Group of palms, Colorado desert, California . . 21

XXVI. Belt of palms, Colorado desert, California 21

XXVII. Vegetation in the Grand Canyon, Arizona 23

XXVIII. Bright Angel trail. Grand Canyon, Arizona , .23

XXIX. Alpine desert on summit of San Francisco inountain, Arizona . . 43

PAGE.

Fig. I. Rainfall map of arid regions . . . . 28

Fig. 2. Copy of map of American deserts, 1835 . . 32

Fig- 3- Copy of map of American deserts, 1859 35

Fig. 4. Meteorological data from San Francisco mountain, Arizona ... 44

THE DESERT BOTANICAL LABORATORY OF THE CARNEGIE INSTITUTION.

Introduction.

Several investigators, in Experiment Stations and other branches of government inquiry, have made special studies of the relations of plants to alkaline and other soils. They have also observed the be- havior of plants in arid regions under the influence of irrigation. For the most part, both of these classes of studies w^ere concerned with special and local problems, the immediate purpose of such study being to obtain information for the use of the agriculturist and horticulturist. Despite this limitation they clearly showed the need of a broader and more thorough study of the technical and general aspects of the rela- tion of plants to dry climates and to substrata of unusual composition. Special mention should here be made of the results obtained by Messrs. Kearney and Cameron, who have investigated the separate and the combined effect upon plants of the substances usually found in alka- line soils. Other important papers are cited in the accompanying bibliography, pages 53 to 58.

When the Carnegie Institution was established, Mr. Coville deter- mined to present to it a plan for a Desert Botanical Laboratory. This long cherished project was an outcome of his work in the Death Val- ley Expedition, in 189 1. A plan was accordingly drawn up by him and presented to the Institution's advisory committee in Botany. This committee considered and approved it because it promised results con- cerning the fundamental processes of protoplasm as important as any in the whole realm of botany. The Board of Trustees of the Institu- tion also approved it, and appropriated $8,000 for the establishment of such a laboratory and its maintenance for one year. Messrs. Coville and MacDougal were appointed by the Institution as an Advisory Board in relation to the matter. This Board decided to place the Laboratory under the immediate charge of a resident investigator, who should carry on researches under its guidance, and should be respon- sible to it in his relations to the Institution. It was planned to begin a few inquiries of wide scope and important bearing to be carried on by the resident investigator until decisive results were obtained.

Furthermore, it was arranged to provide such an equipment as would

I

N. C. State College

2 DESERT BOTANICAL LABORATORY

enable a small number of trained investigators, should they so desire, to utilize the opportunity for studying those questions for whose solu- tion the Laboratory and its environment are especially favorable. Not the least important part of the duties of the resident investigator wrill be to aid visiting botanists and others.

The Laboratory Location Trip.

Each member of the Advisory Board had visited, during the pre- ceding twelve years, most of the more marked desert areas of the country. Nevertheless, it was deemed profitable to make, together, a systematic tour of these deserts in order to gain a better comparative knowledge of the aspects of their vegetation, and to select a locality offering the greatest advantages and facilities for the proposed work. Accordingly, between January 24 and February 28, 1903, they made a reconnaissance of the region along the Mexican boundary. As the outcome a site was selected on a small mountain near Tucson, Arizona, and the erection of a laboratory building, according to plans approved by them, was begun. The organization of the Laboratory was carried a step further by the appointment of Dr. W. A. Cannon as resident investigator. He at once undertook the preparation of the bibliography of desert plants, which is printed in this report, pages 46 to 58.

As no publication exists, suitable to the needs of the botanist who visits our western deserts, it has seemed desirable to present a brief narrative of the trip, accompanied by illustrations of landscapes show- ing characteristic vegetation. The observations were necessarily in- terrupted by night travel, and as the time at command was short, only a mere skeleton of the desert flora can be presented. If, however, this shall serve to convey an idea of the diversity of the several lesser floras of which the whole is made up, and of the wealth of material afforded for detailed geographical and physiological study, the chief purpose of this portion of the report will have been accomplished.

itinerary.

The two members of the Board having met at Washington left that city January 24, 1903, and arrived at El Paso, Texas, on the morning of January 28. During the day they visited the sand dunes in the Chihuahua desert between Samalayuca and Los Medanos, Mexico, and in the evening took the train for Alamogordo, New Mexico. From January 29 to January 31 they were engaged in a wagon trip to the White Sands of the Tularosa desert, southwest of Alamogordo. On February i they returned to El Paso and proceeded by rail to

ARID REGION OF WESTERN TEXAS 3

Tucson, Arizona. Here they remained February 2 and 3, examining the desert flora of the plain and adjacent mountain slopes. On Feb- ruary 4 they proceeded by rail to Nogales, on the boundary line between Arizona and Mexico, where they stayed February 5, making observations on the vegetation in that vicinity. On the morning of February 6 they arrived by rail at Torres, Sonora, Mexico. February 7 to 10 was spent on a saddle trip into the desert west of Torres, toward the Gulf of California. February ii a journey was made by rail to Guaymas and return which afforded an opportunity to observe both the desert and the seacoast flora of Guaymas harbor. February 12 and 13 were passed on the desert in the immediate vicinity of Torres. On February 14 the Board returned to Tucson where they remained during the two following days. On the morning of February 17 they arrived by rail at Salton, in the Colorado desert of southern California, and remained during the day examining the vegetation of the salt and alkali lands. On the morning of February 18 they pro- ceeded to Indio, also in the Colorado desert, and in the afternoon drove to Thousand Palm canyon and return. February 19 they went by rail to Los Angeles and the next morning took a train east, passing through Cajon pass and across the Mohave desert, arriving on the evening of February 21 at the Grand Canyon of the Colorado river, in Arizona. February 22 and 23 were spent in a trip to the river by the Bright Angel trail. On the morning of February 24 they left the canyon and on February 28 arrived in Washington.

THE ARID REGION OF WESTERN TEXAS.

Eastern Texas has the characteristic humid subtropical flora of the Gulf region, with longleaf pine (^Pinus palustris)^ cane (^Arundi- narid)^ bald cypress {^Taxodium dtsticktim) ^ and their associates, but this flora gradually merges into the wholly different one of arid western Texas. Beginning east of San Antonio the ground is covered with an open growth of mesquite trees {Prosopis)^ 10 to 20 feet high, resembling a vast peach orchard. Scattered through it are larger trees, some deciduous, others evergreen oaks. The mesquites them- selves are nearly leafless in late winter and are much infested with a mistletoe. Scattered among them are various shrubs 4 to 8 feet high, and as the most conspicuous feature of the undergrowth a prickly pear with large flat orbicular vertical joints, the whole plant rising i to 3 feet from the ground. Another occasional feature of the undergrowth is a small Tucca with long and broad leaves, commonly without a trunk but occasionally reaching a height of 6 to 8 feet. Some of the oaks have their branches clothed with a gray epiphyte

4 DESERT BOTANICAL LABORATORY

{Tillandsia) . Between Sabinal and Uvalde occur areas on the higher, more sterile parts of the plain, over which the mesquite and oaks are wanting, the undergrowth, however, remaining. These areas often contain a growth of an Acacia 2 to 3 feet high with dark yellowish-green persistent foliage, the whole plant suggesting the creosote bush of the more western desert.

Between Del Rio and Devils River a change in the flora takes place, the sotol (^Dasylirion) becoming the most conspicuous feature of the upland vegetation, with a broad leaved Tucca having a trunk i to 6 feet high, a shorter leaved grayer plant than the one about San Antonio. The Acacia mentioned earlier and various shrubs, chiefly gray leaved and spinose, are also abundant, while the mesquite is small and con- fined chiefly to the ravines. A lechuguilla {Agave) occurs on rocky slopes and thin soils, and a coral bean {Sophora secundijlora), with its shining, bright green leaves, in the canyons.

Between Shumla and Dorso the ocotillo {Fouquieria splendens) and the creosote bush ( Covillea tridentata) appear, interspersed with the large yucca, the lechuguilla growing in abundance on thin rocky soils with acacia, and the mesquite and a small juniper growing in the washes. The area is characterized also by a second smaller species of Opuntia^ in addition to the larger one earlier mentioned, and by an Ephedra^ probably E. antisyphilitica . The ocotillo disappears at an elevation of about 2,000 feet as the plateau west of the Pecos is reached.

THE SAND DUNES OF CHIHUAHUA.

South of El Paso and crossed by the old traders' trail from Santa Fe to the city of Chihuahua is a long stretch of sand dunes which we had determined to examine ; these were familiar to the early travelers but are almost unknown to the botanists of today. Taking a Mexican Central train at Juarez we were put off, through the courtesy of the railroad officials, among the sand dunes, about six miles south of the station of Samalayuca. This station is eighteen miles from Juarez and one mile north of Los Medanos.

The dunes where the railroad crosses them are about forty feet high, with scant winter vegetation consisting of a few w^oody plants, princi- pally a labiate bush {Poliomintha incana)^ an Artemisia^ a Chryso- thamnus^ a Tucca {Tucca radiosa)^ and a suffrutescent Senecio. Two perennial grasses, an Andropogon and a Sporobolus with a spike- like panicle {Sporobolus cryptandrus) ^ are of frequent occurrence as are the remnants of many annual plants. The Tucca takes an impor- tant part in binding the sands ; roots were seen extending in a nearly horizontal direction forty feet from the plant.

Carn. Inst. Wash. Pub'n 6

Plate II

Tree yucca ( Yucca radiosa) in the Tularosa Desert, New Mexico. The large plant.

which is in fruit, has lost some of its lower leaves by the nibbling and rubbhig of

cattle. The two small plants are younger specimens of the same species. "

Carx. Inst. Wash. Prii'x 6

Plate III

C/3 o

Z 5

~ o

THE TULAROSA DESERT 5

From the dunes toward Samalayuca the valley bottom has a vegeta- tion of mesquite mixed with Zizypkus, Koeberlinia spinosa, and Atri- plex canescens. An annual Croton forms a thick spindle shaped tumble weed adapted for rolling only along one axis.

The highest part of the dunes is not crossed by the railroad but lies east and southeast from Samalayuca about five miles and apparently rises 200 to 300 feet from the plain.

About nine pounds of the material of which the dunes were com- posed was collected by removing a thin surface layer and then placing in a cloth waterproof bag. This material was forwarded to Dr. W. J. Gies, consulting chemist to the New York Botanical Garden with the request for an analysis. Dr. Gies' report is printed on pages 10 and II of this pamphlet.

THE TULAROSA DESERT.

Starting westward from Alamogordo, New Mexico, across the Tularosa desert, one first enters a region characterized by low mesquites, commonly 3 to 6 feet high, with an abundance of Atriplex canescens and Koeberlinia spinosa. That the soil is alkaline is in- dicated by a surface deposit along an irrigating ditch. The ground bears also an abundance of a suffrutescent Suaeda^ a bunch Sporobolus with expanded panicles, and occasional specimens of a Lyciuni. In low spots and along the margins of clay bottomed washes, an incrus- tation of alkali appears, accompanied by Allenrolfea occidefitalis. In this area water is commonly found in wells at a depth of 50 to 70 feet. Toward the middle of the valley the mesquite disappears, and the principal bush vegetation is Atriplex canescens^ with a great deal of the Sporobolus and areas in which Tucca radiosa (Plate II), or Opuntia arborescens^ or another Opuntia^ conspicuous at this season by its scarlet fruit, are abundant. The wagon road in this part of the valley often strikes at the depth of a foot the so called caliche rock, a sort of hardpan. Ground water is presumably to be found only at a great depth.

Our principal object on this trip into the Tularosa desert was to examine the flora of a remarkable area of drifting sand it contains, known as the White Sands, composed not of silica but of gypsum, and estimated to cover an area of 10 by 40 square miles (Plate III) . These sands are most easily reached at a point about 20 miles southwest of Alamogordo. Here there are some water holes where horses when forced by continued thirst can be watered with safety. Water for men, however, must be carried from Alamogordo.

Two principal plant formations occur in the bottoms and the dunes

6 DESERT BOTANICAL LABORATORY

of the White Sands. The bottoms occur at nearly the same level as the surface of the plain surrounding the sands, the dunes are irregular heaps and ridges of white gypsum sand, rising to a maximum height estimated at 60 feet. When moist the sand is of a slightly yellowish or buff color, when dry almost pure white. When taken in the hand it has not the sparkling effect of silicious sand, but its grains are dull even in sunlight. As compared with silicious sand it may be likened to corn meal, the other to granulated sugar. The separate grains can be rubbed between the fingers to a fine white powder. Except on steep slopes the dunes of the White Sands form an excellent surface for walking, comparable in hardness with a sandy seabeach wet by an outgoing tide. These hard surfaces are covered everywhere with rip- ple marks caused by the wind.

The most characteristic plant of the dunes is the threeleaf sumac {Rhus trilobata)^ which occurs in the form of single hemispherical bushes 4 to 8 feet high, the lower branches hugging the sand. The plant grows vigorously, the trunk at or beneath the surface often reaching a diameter of 3 inches. The binding and protecting effect of this bush is often shown in a striking manner when in the cutting down of an older dune by the wind a column of sand may be left pro- tected above from the rain by the close covering of the branches and leaves, and the sand in the column itself bound together by the long penetrating roots. An incrustation, apparently of gypsum, is often found on dead roots. One of these columns was about 15 feet high fi-om its base to the summit of the protecting bush and about 8 feet in diameter at the base (Plate IV) . A curious fact brought out in the denudation of the underground trunks of this plant by the shifting of the dunes is the abundant exudation of a pale amber gum with the char- acteristic aroma of the crushed twigs. This, mixing with the sand, forms hard honeycombed masses sometimes three inches in diameter.

Other characteristic woody plants of the dunes are Atriplex canes- cens^ two species of Chiysothamnus ^ and Yucca radiosa. The under- ground trunks of the Atriplex often attain a diameter of four inches, those of the Yucca six inches. A marked peculiarity of the White Sands is that a cottonwood is occasionally found in the lower dunes, reaching a foot in diameter but seldom more than fifteen feet in height ; yet at the same time not a mesquite was seen. The mesquite is a tree requiring less moisture than the cottonwood. Apparently the presence of an excess of lime is prejudicial to the growth of the mesquite.

The bottoms among the dunes have a dense vegetation as compared with that of the dunes themselves. It is characterized especially by the

Carn. Inst. Wash. Pik'n 6

Pr.ATK I\-

Carn. Inst. Wash. Pl b'n 6

Platk V

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Carn. Inst. Wash. Plisn 6

Plate VI

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Carn. Inst. Wash. Pib'n 6

Plate VII

y'«<" nnhos,r growing up through a dune 30 feel high, White Sands. New Mexico .\ tew of the upper circles of leaf bases can be seen in the picture.

C\RN. Inst. Wash. Pib'n 6

Plate VIII

1)

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k5 -O

c cs

THE TULAROSA DESERT 7

presence of a grama grass {Bouteloud) forming almost a turf, and by frequent clumps of an Ephedra^ of a grayish purple color at this season and with 3-scaled nodes (Plate V). These bottoms usually show no sign of moisture, but in two places we found water holes, the water so alkaline that the horses would not drink it at the end of their first day's drive. About both holes occurred salt grass (^Distichlis spicata) and wire grass {Jtmcus balticus)^ both of them character- istic of moist alkaline soils (Plate VI).

In addition to their woody vegetation the White Sands appear to have an abundant herbaceous vegetation which would well repay care- ful systematic and ecological study. The area they cover is large, probably 400 square miles or more, the physical and chemical proper- ties of the soil are very unusual, and no botanist has yet thoroughly studied the vegetation.

The relation of Yucca radiosa to the sand dunes is unusually inter- esting. A group of four small yucca plants standing about three feet high to the tip of the highest leaf, was found upon the summit ridge of a thirty-foot dune. We dug the trunk out to a depth of 14 feet. All four plants were from branches of the same trunk, the lowest branch arising about 16 feet from the base of the dune ; the main trunk and the branches bore marks of rosettes of leaves at intervals all the way to the lowest point reached. The trunk was thicker here, about 4 inches, than at any point above. The strata in the cut showed that the yucca once stood on the front slope of the dune. The trunk sloped in the direction in which the dune was moving. In the plain in front of the dunes were occasional low plants of the same species of yucca. Con- sidering all the evidence the conclusion is irresistible that the yucca originally grew on the plain, was engulfed by the sand, and gradually grew through each successive layer of sand that drifted over it, until the summit of the dune was reached. In the vicinity, at the rear of the dune, were other long trunks partly denuded by the passing of the dune (Plate VII) .

A gentleman, familiar with the White Sands for twenty years, told us that in that time they had advanced eastward at one point, the one of greatest activity, about half a mile. A road traversing the plain in a north-south direction close to the eastern front of the sand showed fre- quent changes necessitated by the advance of the dune (Plate VIII).

A section from the base of the Sacramento mountains southwest through Alamogordo into the White Sands, shows four belts : ( i ) the delta slopes from the mountain canyons, characterized by a nearly pure growth of creosote bush (^Covillea tridciitata)^ the soil usually grav-

8 DESERT BOTANICAL LABORATORY

elly and probably washed nearly free from alkali; (2) the mesquite area already described; (3) the Atriplex area also already described, and (4) the White Sands.

The Tularosa desert as traversed by the railroad from Alamogordo south to El Paso has a red and apparently mellow soil, the most char- acteristic plant of which is Yucca radiosa^ sometimes associated over large areas with grass, but often associated with low mesquites, the latter in some spots gathering large hummocks of earth from drifting dust, out of which the twigs of the mesquites project. A large Ephe- dra is also a frequent associate of the mesquite and yucca. The rail- road traverses only a little of the creosote bush foot slopes of the moun- tains.

Analyses of Sands. The following report on the gypsum sand from the White Sands of the Tularosa desert and on sand from the Chihua- huan desert has been received from Dr. William J. Gies :

Gentlemen : I present herewith the results of my chemical analyses of the two samples of sand expressed by you to me from Tucson, Arizona, on February 16 and received by me on February 24 :

SAMPLE I. locality: TULAROSA DESERT, NEW MEXICO.^

General Descrij)tio7i. Color white to delicate cream, with occasional very minute black particles. There were also a few reddish and yellowish-red grains. Now and then red specks could be detected in the white grains. Glassy grains of silica were present. Nearly all the grains were very small, about the size of those in ordinary sea sand. A few larger masses were made up of many of the small grains cemented or fused together. These masses were more cream colored "than the small grains, some contained a dark nucleus. They varied in size from such as were only three or four times the bulk of the uniformly small grains to a few which were nearly as large as a pea. No special crystalline qualities were observed in any sample of the sand. The grains were angular, or rounded by erosion. Fragments of elytra of beetles were detected and oc- casional pieces of hair, and small splinters, were also seen.

Before subjecting the sand to analysis it was passed through a copper sieve the meshes of which were just large enough to permit the passage of the typical and uniformly-sized grains. Only a few grams of material consisting of the larger fused particles, elytra of beetles, hair, etc., was separated in this way from four kilos of the sand as received. All of this material was regarded as extraneous matter, and only the main bulk of the sand was analyzed quantitatively.

Qualitative Data. The sand dissolved readily in water and in dilute acids, leaving only a slight residue of silicious matter. The black particles in the sand seemed to be entirely insoluble in these media. The aqueous solution was neu- tral to litmus. The hydrochloric acid solution was slightly yellowish in color, due doubtless to the presence of iron. On diluting the hot concentrated sul- phuric acid solution, crystals of calcium sulphate quickly separated. On ignit- ing the sand it immediately blanched, and abundance of water was evolved, but the sand did not fuse, even in platinum, over a blowpipe. Extraction of the

ANALYSES OF SANDS 9

ignited sand in water gave a solution slightly alkaline in reaction. Only a minute trace of carbonic acid gas could be produced from the sand on ignition, a fact showing that practically no organic matter is contained in it. Such organic matter as was actually present in the few particles separated from the sand con- sists, as already stated, of the fragments of insects, e.\creta of animals, etc., and is too slight in quantity to have much significance as nutrient material for plants.

On drying a sample of the sand, in an air bath at lOo" C, it soon became translucent and finally snow white. The grains retained their original shape. Water of crystallization was eliminated in abundance. The sand contains traces of sodium phosphate and chloride. The larger particles removed with the sieve contained a more decided quantity of chlorine, 0.7 to 0.9 per cent. Quantitative Analysis.

Preliminary Data.

A. Sand dried in an air bath at 30°-35° C. :

(a) On drying to constant weight in an air bath at iio°-i20° C. the quantity of water eliminated was 19.9 per cent.

(d) On drying to constant weight in an air bath at 50°-6o° C. the weight of the substance remained the same.

(c) On continuous percolation at room temperature of small quantities of dis- tilled water at a time over the sand, until about 100 parts water to one of sand was used, 79.9 per cent, of the sand was dissolved and only 20.1 per cent, of it remained as residue. The latter was still dissolving when the experiment was discontinued and further percolation would have reduced the amount of residue (see under B., [d) 4 below).

(d) On continuous percolation, as above, with distilled water at 30° C. the dissolved matter amounted to 87.1 per cent., and the residue to only 12.9 per cent. Further percolation would have decreased the weight of the residue (see under B, {d) 3 below).

B. Sand dried in an air bath at iio''-i20^ C.

(a) On ignition in a platinum crucible over a blowpipe the loss of weight was I.I per cent.

{&) On,treatment for three hours with about i liter of hot acids, hot water or cold water per gram of substance the following data were obtained :

Substance Dissolved.

Residue.

One part HCl and three parts HjO

Two parts HNO3 ^"^ two parts H,0..

Boiling HjO

Cold HjO (X5°C.)

Per cent. 97.4 97.8 94-3^ 96.4

Per cent . 2.6 2.2

5-7 3-6

Some General Deductions. The analytic results set forth in the above table and in that on the following page show that the sand is mainly composed of grains of calcium sulphate derived from crystalline gypsum. Silica and also silicate of iron and aluminum are present in small amounts. Insignificant quan- tities of soluble substances such as chloride (probably of calcium) may also be detected.

The sand is free from nitrogenous matter except such minute "amounts of animal ddbris and excreta as have already been referred to.

'Calcium sulphate is more soluble in cold than in hot water.

DESERT BOTANICAL LABORATORY

Percentage Composition. Sand dried at 30°-35°C. and at iio°-i20°C.

CaO ....

SO3

SiOj .... Al,03 ) Fe,03 /

H,0

Traces : Calcium Calcium

O, CI, Na, PO< (by difference)

sulphate, CaSO^.aHjO

sulphate, anhydrous

Per cent.

30-4

44-5

2.8

0.4

IL

Per cent. 31.2

43-9 2.6

0.4

20.8

Average.

Per cent.

30.8

44.2

2.7

0.4

20.8

95-8 750

Average. Per cent.

38.5

55-1 3-4

0.5 I.I 1.4

93-6

It is very evident that the sand readily dissolves in w^ater. Every rain, no doubt, dissolves some of it and the waters in the district from which the sand was obtained must be heavily charged, probably to the saturation point, with gypsum. On the evaporation of such water, in the sand or in pools, calcium sulphate is again rapidly deposited.

SAMPLE II. LOCALITY : SAMALAYUCA, CHIHUAHUA, MEXICO.

General Description. A composite sand, yellowish to light brown in general appearance. No crystals were detectable in it. The grains were of irregular shape, but of fairly uniform size. None were any larger than the small uni- formly sized ones of Sample I. The grains were angular, with the edges showing the effects of erosion. Glassy and brownish grains predominated. Others with the following colors were to be seen : Amethyst, dull white, dirty yellow, purple, black and red.

All of this sand passed readily through the sieve used on Sample I. No ex- traneous matter was found in It.

Qualitative Data. The sand was very resistant to the solvent action of water, alkalies and acids, scarcely anything dissolving in these fluids, hot or cold. The colored grains were somewhat reduced in number after treatment with acid, the solution in hydrochloric acid having a yellowish tinge. The sand fused with sodium carbonate with great difficulty. The fused mass was bluish-gray in color. On ignition the sand lost only a slight amount of water. It became pink and yellowish-red in places but did not fuse, even in platinum over a blowpipe. Carbonic acid gas could not be obtained from it on ignition, so that the sand is obviously entirely free of organic matter. On drying at iio°-i2o° C. no change in appearance occurred. This sample contained also minute amounts of calcium, sodium, fluoride, sulphate, phosphate, titanate. Quantitative Analysis.

Preliminary Data.

A. Sand dried in an air bath at 30°-35° C :

(a) On drying to constant weight in an air bath at 50°-6o° C. the quantityrof water eliminated was o.i i per cent.

{b) On drying to constant weight in an air bath at iio°-i20° C. the quantity of water eliminated was 0.19 per cent.

B. Sand dried in an air bath at iio°-i20° C. :

(«) On ignition in platinum over a blowpipe the quantity of water elimi- nated was 0.5 per cent.

ANALYSES OF SANDS

{l>) On treatment for three hours with about lOO parts of hot acids, hot water, or cold water per unit of substance the following data were obtained :

Substance Dissolved.

Residue.

One part HCl and three parts HjO.

Two parts HNOj two parts HjO

Boiling HjO

Cold HjO (i5°C.)

Percent. 30 2.6 05 06

Per cent. 97.0 97-4 99-5 99-4

(c) In a percolation experiment similar to those on Sample I, only 0.4 per cent, of the substance dissolved, 99.6 per cent, remaining as residue. Percentage Composition. Sand dried at iio°-i20° C.

Average.

SiO,

Al.Os \

Fe,03 ;

Water

O in silicate, plus traces, Ca, Fl, SO^, etc. Silica and insoluble silicate, not less than.

Per cent.

85.9

81

0.6

Per cent. 86.1

8.3 0.4

Per cent. 86.0

8.2

0.5

5.3

95.0

General Conclusio7is. This sand consists chiefly of silica and of insoluble silicates of iron and aluminum. The results of the extraction experiments, in which relatively large amounts of acid, alkali, and water affected it very little, show that the sand is one of the most insoluble and resistant varieties, and that it is not rapidly altered by weathering influences.

COMPARATIVE COMPOSITION, SAMPLES I AND II.

Direct comparison of the results for composition of the two sands is made in the appended summary of average analytic data for substance dried to constant weight at iio°-i20° C. :

Sand dried at iio°-i20° C.

CaO. SO,. SiOj, AI2O. Fe. " H

I2O3 \ ,0

O in silicate and traces of other elements (by difference).

Chief constituents : Calcium sulphate ,

Silica and silicates ,

Sample ]

Per cent.

38.5

55-1

3-4

0.5 I.I 1.4 936 3-9+

Sample II.

Per cent, trace trace 86.0

8.2

05 5.3

94.2+

Sample I, from Tularosa desert, consists mainly of gypsum. Sample II, from Samalayuca, is almost entirely silicious.

Respectfully submitted,

William J. Gies.

\^est of El Paso, within the valley of the Rio Grande the character- istic vegetation, above the moist bottom, is creosote bush, with some

12 DESERT BOTANICAL LABORATORY

ocotillo and lechuguilla on rocky places. The soil under the creosote bush is almost always gravelly.

As the road rises, near the station of Strauss, to the plateau and crosses it westward at an elevation of a little more than 4,000 feet, the same flora appears as that of the Tularosa desert; mesquite, Tucca radiosa^ and grass, or either of these plants alone with the grass, and Ephedra a frequent accompaniment. Creosote bush occurs only oc- casionally and on gravelly slopes near desert hills.

TUCSON AS A LABORATORY SITE.

The woody vegetation of the desert in the vicinity of Tucson con- sists chiefly of creosote bush ( Covillea tridentatd) interspersed with several species of Opuntia^ most of them with cylindrical stems (Plate IX), and occasional plants of joint pine {Ephedra triftirca^ and barrel cactus {Echinocactus), w^ith an abundance of mesquite {Pro- sopis^ and cat's claw {Acacia greggii) (Plate X) in the lower drain- age areas. Upon the foothills occur in addition the giant cereus( Cereus giga7iteus^ see frontispiece), two species of palo verde {Parkinsonia microphylla ixnd P. torrey ana) ^ocoiiWo {Fouquieria splendens)^ two species of Lycluni and many other woody plants. This is of course in addition to a great variety of annual vegetation which may spring up between the sparse shrubs after any drenching rain, particularly the repeated slow rains of winter.

In recommending a site for the Laboratory the Board kept in mind four principal requirements :

1 . A distinctly desert climate and flora.

2. A flora as rich and varied as possible, while still of a distinctly desert character.

3. Ready accessibility.

4. Habitability.

Much of the arid region of the western United States is only par- tially or relatively arid and does not therefore contain those pronounced types of drouth resistant vegetation which it is the first object of the Laboratory to investigate. Such semi-desert areas are the western por- tions of Kansas and Nebraska, and the intramontane valleys of south- ern California. Another sort of location, to be avoided for a like reason, was a desert which was likely to be reclaimed by irrigation, such as that about Phoenix, Arizona. The desert character of a small area, even though carefully reserved, might be seriously modified by seepage or other changes following irrigation development in the vicinity.

Carn. Inst Wash. Puh'n 6

Plate IX

w

■mm

IIH

^H

■;^lm

^H

'^J^spBR^^HI

^B

J

1

'^1

■1

s.^^^^U

1

yM

-1

BPfCW^H^UB^MK- ^

("^mwH^k

^ i= a. /= bo u

_c o ^

'Sot;

c o ■;=

^ E, so

C « -4-,

*j ' o

Carn. Inst. Wash. Pu»"n d

Plate X

TUCSON AS A LABORATORY SITE I3

Some of our deserts, such as the Mohave, the Colorado, and the lower part of the Gila, are of such extreme aridity that only a small number of vegetative types occur in them. The same paucity of vege- tative types is usually characteristic of any flat area of desert as distin- guished from a foothill, canyon, or mountain area, a broken and rocky soil giving a wider range of temperature and moisture conditions of both soil and air, and furnishing lodgment for a greater variety of plants. The yucca plains of the Tularosa desert in New Mexico and the sage plains along the Snake and Columbia rivers in Idaho, Wash- ington, and Oregon are examples of deserts in which a pronounced paucity of woody species is correlated not with extreme conditions of aridity but with flatness of surface.

The members of the Board are acquainted with several charming situations in the mountains of the desert, remote from civilization, rich and remarkable in their flora, furnished with an abundance of pure never failing water, and altogether delightful in their surroundings. Such situations are often chosen for army posts and they are and will always remain treasure spots for the camping naturalist. For the pur- pose of a laboratory, however, they are objectionable for several rea- sons. Such a situation involves first of all the maintenance of a hotel or its equivalent, a feature that would tend to exhaust the financial and mental resources of the management of a laboratory. Furthermore, severe isolation for long periods would doubtless have a depressing instead of an exhilarating effect on some research workers, and the solicitude of friends and relatives would doubtless in some cases be a bar to residence at such a place.

The conditions of living at some spots in the desert suitable in other respects for laboratory purposes are so severe as to offer an obstacle to the best work. A period of such extreme heat as occurs in summer at some points of very low elevation, as for example along the lower Colorado river or in the vicinity of Guaymas, Sonora, or the difiiculty of getting pure water and good food, has been an effective argument against some otherwise good locations.

Viewed from the standpoint of these primary requirements Tucson has a climate of a thoroughly desert character, and a flora, including mountains and plain, rich in species and genera. In addition to its situation in the heart of the desert of Arizona, it is centrally located, both as to position and transportation, with reference to the deserts of Texas, Chihuahua, New Mexico, California, and Sonora. The city has a population of about 10,000. It is situated on a transcontinen- tal railroad, the Southern Pacific, less than four days' railway travel

lA DESERT BOTANICAL LABORATORY

from New York, about one and a quarter days from San Francisco, and seventeen hours from Los Angeles. The Laboratory will be con- nected with the city by telephone, and thence it will be in communica- tion by telegraph and cable with as much of the world as the sender of a message may require. The business of the city and the conduct of its municipal affairs are largely in the hands of progressive Americans- The members of the Board, while outfitting at Tucson for a short trip to the Santa Catalina mountains, found a provision store that would have done credit to a metropolis. The elevation of Tucson is 2,390 feet, while the highest