FOREST TREES OF THE PACIFIC SLOPE. 201 



YUCCA. YUCCAS. 



The tree yuccas are characterized by their bristling, stiff, upright, bayonet-like, 

 sharp-pointed leaves, which arc thickly clustered at the top of the anbranched 

 young trunk or at the ends of the few large club-like branches of old trees. 

 The edges of the leaves of different species are either smooth (unbroken), rough 

 with minute teeth, or with a few thread-like fibers. Toward their ends the 

 edges of the leaves are often conspicuously rolled or turned toward each other 

 (on the upper side), giving the top end of the leaf a trough-like form. The 

 leaves of each season's growth remain green for several years; later they begin 

 slowly to bend down, close to the trunk or branch, and finally they <lie and 

 within a few years fall from the tree. Bark of the tree yuccas is rather thick 

 and cork-like, and furrowed and checked as in ordinary trees. The large wax- 

 like showy flowers are perfect (male and female organs in same flower), and 

 appear iu big branched clusters from among the topmost leaves. With one ex- 

 ception (Y. aloifolid, which is self-fertilized), they are so constituted that they 

 can be cross-fertilized only through the visits of insects (moths). The fruit (of 

 Pacific species), matured in one season, resembles a small cucumber in form 

 (about 3 to 4 inches long; fig. SI), or in some species a large butternut of the 

 same dimensions (fig. 79). In some species it stands erect on the flowering 

 branches; in others, it hangs down. It is indistinctly 6-sided with 6 Separate 

 cells, each containing numerous thin, flat, black seeds. The fruit may have a 

 thin, fleshy, outer covering, which dries upon the shell when the seed chambers 

 do not open of their own accord, or it may consist of a stiff, brittle shell, some- 

 times tending to split open at the top, but usually remaining closed. Such fruits 

 fall from the tree in a dry and brittle condition and are carried some dis- 

 tance from the parent tree by wind or water. Finally they are broken open 

 and the seeds scattered. Large quantities of yucca seeds are eaten by rodents. 

 Birds, which feed on the fleshy fruit covering, also assist in distributing the 

 seed. .Many seeds are blighted by insects (moths), to the attacks of which 

 flowers and fruits of yuccas are especially subject, but upon which the flowers 

 depend entirely for fertilization. 



The tough, fiber-like wood of yuccas is of little commercial value at present, 

 but should be useful for paper pulp. The tree merits the forester's attention as 

 a means of helping to maintain much-needed tree growth in arid southwestern 

 plains and foothills. 



Two tree species occur within the Pacific region, and here only in southern 

 California; elsewhere they range eastward into the southern Rocky Mountain 

 region and northward, one extending into Lower California. The yuccas are of 

 ancient origin, remains of them having been found in the Tertiary period. 



Joshua Tree. 



Yuccn wrborescens (Torr.) Trelease. 



DISTINGUISH I XG CHARACTERISTICS. 



Of the two tree yuccas indigenous in the Pacific region the Joshua tree, also 

 called "yucca cactus," is much the larger and more tree-like (fig. 79). Prom 

 18 to 25 feet, or occasionally 30 or 35 feet, is the usual height, with a diameter 

 of from I to 2 feet. It is easily the most wild-looking denizen of desert hills and 

 plains. The keenly pointed bayonet-like leaves, bristling at the ends of big 

 clumsy branches, defy every intrusion and compel respect from many natural 

 enemies. Young trees are unbranched (fig. SO, a) until they have produced flow- 



