species, as well as on the depth to perennial soil-moisture, or in other words, the water relation.
The three species of oaks referred to are Quercus agrifolia, the encina oak, Q. lobata, the roble oak, and Q. Douglasii, the blue or Douglas oak. The roble oak and Douglas oak are deciduous. The encina oak is the familiar live-oak of the coastwise valleys.
The roble oak is the valley oak par excellence, and is probably the largest California species of the genus. The largest specimen reported is 150 feet in height and 25 feet in circumference four feet above the ground.[1] The writer also saw a specimen near Clear Lake, which had a spread of top estimated to be 144 feet. In addition to being of large size, the roble oak is unusually beautiful and graceful, with long and slender pendant secondary branches, which occasionally nearly sweep the ground. If not strictly confined to moist soils, it at least attains its best development where the soil is moist and the depth to the level of perennial water is not so great as to be beyond the reach of the roots.
The encina oak is the species characteristic of the valleys of the coast ranges, where it finds its greatest development. It is disposed in open groves and it is to this species, mainly, that the park-like appearance of the coast valleys is due. In form, the encina oak is more compact than the roble oak, and has low, rounded tops, as is indicated by the accompanying figure.
As distinguished from the two other species of oaks just mentioned, the blue oak occurs characteristically on dry, rocky soils, "which are excessively arid in the rainy season."
Not in itself an attractive tree, the blue oak, by reason of its form, color and habit, plays a strong and a natural part in the scenery of the yellow-brown foot-hills.[2]
Like the encina oak. the blue oak occurs singly or in open groves. The characteristic appearance of the tree and its distribution are shown in Figure 1.
However the species of oaks may differ from one another in habit, or however different the habitats they frequent may be, they agree in the one particular which has already been mentioned, namely, in the open character of the stand. This phase of the study of the oaks received particular attention at the hands of the writer in 1913, and the leading conclusions will be presented in the subsequent paragraphs.
Quercus lobata
An examination of the roots of the three species shows a striking difference in the position occupied by them in the ground, as well as in the general character of development. That of the roble oak is more of
