ADAPTIVE MODIFICATIONS OF SHRUBS. 49 



Encelia farinom.—'Yha wood of old stems is moderately hard, but the annual rings 

 are indistinguishable. The bark is closer and more compact than in any of the other 

 plants hitherto described. The leaves are large, ovate, sometimes 8 cm. long, and 

 are provided with a thin, close covering of unicellular, simple, entangled hairs. 



Encelia frutescens. — The leaves, which are similar iu form to those of the last 

 species, but smaller, havea rather scant covering of slightly appressed, sharp-pointed, 

 thick-based, stiff hairs, each composed of 3 to 5 cells. 



Ephedra nevadcmu and E. trifurca.— Like all the other species of the genus, these 

 plants have no herhaceous leaves, but carry on transpiration by means of the epi- 

 dermis of the stem. That organ is devoid of any hairy coating but is conspicuously 

 cuticularized. 



Eurotia lanata.—Tke linear-oblong leaves are covered on both faces by a coat of 

 loose, stellate hairs. 



Franseria dumosa. — The wood is hard and of slow growth, but the annual rings are 

 indistinct. The bipinuatifid leaves and the young branches are coated densely by 

 a series of overlapping straight, white, stiff, 2- to 5-celled hairs. 



Grayia spirwsa.— The wood of the branches is hard. The leaves when in the bud 

 are densely covered with short, white hairs of a very peculiar pattern. They are 

 unicellular, rather thick-walled, and much branched. The branches are short and 

 thick and somewhat loosely interlocked, the mass formed by a single hair being 

 nearly isodiametrical. As the leaf attains its full development in the spring, the 

 hairs become separated so that they appear iu abundance only at the apex of the 

 Leaf. 



Krameria canexcenn and K. parv\folia. — The leaves and young shoots are covered 

 with a dense white coat of unicellular, straight, slender, thick -walled hairs. 



Larrea tridentata— The leaves, when young, and the sepals, are coated with a silky 

 covering of long, straight, white, appressed hairs. Later in the season the leaf is 

 protected from desiccation by the resinous substance which pervades its tissues and 

 often exudes on its surface. 



Lyeium andersonii. — The wood is hard aud the rings indistinct. The small, oblan- 

 ceolate leaves are glabrous anil thick, and after accomplishing the various functions 

 of assimilation in the spring months they turn yellow and drop off. 



Lycium eooperi.— The wood is like that of the last species, and the leaves, of similar 

 form but of larger size, are covered with short, glandular hairs. 



Mamillaria deserti and M. tetrancutra have short, thick stems similar to those of 

 Echitiocactus poljucphalus, but smaller and usually single. 



Opuntia basilaris, (). eehinocarpa, and 0. ramosissima. — The first of these has flat, 

 pad-like stems practically devoid of vegetative leaves, while the other two have 

 cylindrical, areolato, branching trunks and rudimentary leaves that fall very early in 

 the summer. 



Peveephyllvm achottii.— The leaves are 2 cm. or less long, glabrous, nearly terete, 

 canaliculate along the upper side, punctate throughout with impressed glands, and 

 usually exude a resinous substance. 



Saiazaria mexicana. — The wood is soft, one stem attaining a diameter of 4 mm. 

 in four years. The epidermis of the young branches, which are green and assimila- 

 tive, is canescent with a coating of pendant hairs similar to those (if Cassia armata. 

 None of the hairs, however, seem to be chlorophyllose, and their exposed portion is 

 not so turgid as in the hairs of the Cassia. The leaves often present two surfaces of 

 1 sq. cm. each and aro nearly glabrous, but show a scant evanescent remnant of hairs 

 similar to those of the stem. They aro early deciduous. 



Sarcobatus vermimlatus. — The stems are white-barked when young, gray when 

 older, have hard, greenish wood, and often attain a diameter of 4 mm. in two years. 

 The leaves are nearly terete, fleshy, and glabrous. 



Tetradymia comom.— The stems, involucral bracts, and linear leaves of this shrub 

 are whitened with an arachnoid but close and persistent pubescence. 

 13095— No. 1 4 



