33§ 



POPULAR SCIENCE MONTHLY. 



v. 



CX'OTILLO. 



M »s 



plied with a meager foliage of compound leaves. The very small leaf- 

 lets, which are foliar members of the third order, are sensitive, the 



pairs folding together at night 

 and opening at dawn. Closure 

 again occurs at the period of ex- 

 cessive insolation. All the ulti- 

 mate branchlets taper into long 

 stiff thorns, an example of direct 

 metamorphosis, since they origin- 

 ate as normal shoots. In the ab- 

 sence of leaves it is evident that 

 the chlorophyll tissues of the stems 

 are chiefly concerned in the food- 

 making process, which would ap- 

 pear true also from the fact 

 that the smaller branches and 

 twigs are used as green forage for 

 horses in winter. Although a 

 particular branch removed from 

 the tree and regarded alone is a 

 rather graceless object, the whole tree with its smooth green bark and 

 gradually tapering limbs and twigs is singu- 

 larly beautiful, its outline most delicate. 



Conspicuous as a member of the hillside 

 vegetation is the ocotillo (Fouquieria sple?i- 

 dens), a plant with a hypothetical relationship 

 with the willows, but not in the least suggest- 

 ing them by its habit and more obvious struc- 

 tures. The general disposition of its branches, 

 which are highly suggestive of coach whips, is 

 similar to that in the creosote bush. It is, how- 

 ever, a much taller shrub, with lithe, bespurred 

 stems, bearing in spring each a brilliant mass 

 of scarlet flowers. On the advent of the rains, 

 the stems are quickly and completely clothed 

 with rosettes of light green ovate leaves, each 

 rosette in the axil of a thorn. Most interesting 

 is the manner in which the thorns arise. The 

 new shoots produce first the primary leaves, in 

 the stalks of which a hard tissue is developed. 

 Their leaf-blades rather soon wither away, and 

 split away from the harder part of the stalks, which in this way 

 are left as spines, in the axils of which, as above stated, the second- 



Twjg of Ocotillo. 



