In all these localities, it is a small tree, from twenty to thirty feet high, and from six to fourteen inches in diameter. It retains its lowest branches, which spread generally very much, often horizontally. The foliage seems to me less dense and less vivid-green, than that of the preceding. Young trees raised here, side by side, show the same differential characters. The cones from all these different localities are very uniform, and differ essentially from those of _Pinus insignis_ at Monterey. The seeds, however, resemble each other very much. Both species grow near the coast, but on different soil. _Pinus insignis_, on a soil produced by the disintegration of a bituminous slate and granite; _Pinus tuberculata_, in all the above-mentioned localities, on a soil derived from metamorphosed sandstone. Should these two species be definitely united, after a thorough investigation, they would afford a most striking example of the influence of a different soil. It is certainly singular to find such a well-characterized form restricted to one locality only. This fact, however, would not stand isolated with us here; _Abies bracteata_, we find similarly confined to one locality only in California. Isolation is more or less a characteristic feature with all our trees, and there is probably no country where the influences of soil, climate, and exposition are so well and abruptly marked and unmistakably defined. 6. _Pinus muricata_, Don. Monterey! Mendocino City! In a moist depression at Monterey, I found a small group of this species, averaging about fifteen feet in height, and five to six inches in diameter. Bark reddish and nearly smooth; branches almost at a right angle with the main axis and generally from five to seven in a whorl; leaves of a darker vivid green, and more succulent and longer, than those of _Pinus insignis_, of which there were trees of the same size by the side of it; cones from three to seven, in a whorl very much aggregated and clustered. I counted seventeen whorls on a tree fifteen feet high. The lower portion of the trunk was clad with dead leaves. At the same distance (about two miles) from the ocean, and scarcely a mile from the above-mentioned depression, I found another group (mixed with _Cupressus macrocarpa_) in a deeper but drier locality. Here the tree was altogether of a different aspect, inferior in all its parts. This very transition suggested strongly, that this pine and the one previously seen on the plains near Mendocino City, on a similar soil, might be of the same species. Near Mendocino City, on the so-called plains, I found in great abundance a small pine tree, which I refer for the present to this species.