rOEEST TREES. 



197 



remain a monument to the industry and scientific attainments 

 of the authors, but recent discoveries, especially in the Eocky 

 Mountain regions and westward, has not only added many new 

 species of the oak, but has also made it necessary to revise some 

 of the earlier classifications of the members of this genus. The 

 late Dr. George Engelmann, of St. Louis, Mo., a most capable 

 botanist, devoted much time to the study of the oaks, and ]3ub- 

 lislied an excellent paper on the subject in the Transactions of 

 the Academy of Science, of St. Louis, Vol. Ill, 1876, and also 

 elaborated the oaks of California for the Botany of California, 

 edited by Sereno Watson, issued as supplementary volumes of 

 the Geological Survey. I accept Dr. Engelmann's arrangement 

 of the species, but may add that he was well aware of the diffi- 

 culties to be met in attempting this work, for in the paper re- 

 ferred to, in speaking of the many varieties of the Rocky 

 Mountain scrub-oak, he says : ''If one oak behaves thus, why 

 not others ? Thrown into a sea of doubt, what can guide us to 

 a correct knowledge." Having spent many months among 

 these scrub-oaks, I am fully aware of the difficulties to be met 

 in trying to determine where a variety ends, and a species be- 

 gins, consequently am more than willing to throw the responri- 

 bihty of separating them upon some one else." 



Qnercus agrifolia, Nee. — Encino Holly-leaved Oak. — Leaves 

 oval to oblong, two to three inches long, usually obtuse or 

 heart-shaped at base, the uneven margins with spine-tipped 

 teeth, but these are sometimes absent. Petiole or leaf -stalks 

 downy. Acorns sub-sessile or sessile, solitary or in clusters, 

 maturing the first season, slender, and one to one and a half 

 inches long, and about one-third of an nich broad. This is one 

 of the Black Oaks. A large tree, with very thick gray bark, 

 and wood rather cross-grained and perishable. A very pictur- 

 esque oak, with very stocky stem, sometimes twenty feet in 

 circumference, and Prof. Brewer reports specimens near Mount 

 Diablo, with a spread of branches of one hundred and twenty 

 feet. A variety {Q. agrifoUa, var. frutescens), is only a shrub, 

 three to five feet high. A common tree in the maratime portion 

 of California. 



alba, L.— White Oak.— Leaves whitish, pubescent while 

 young, but soon become smooth, bright green above, with 

 three to nine oblong or linear-obtuse, mostly entire oblique 

 lobes. Leaves very persistent, many remaining on the trees all 

 winter, and only fall when pushed off by the expanding buds 



