TREES OF SOUTHERN EUROPE. 309 
In the walnut, the chestnut, the cork oak, the mulberry, the 
olive, the orange, the lemon, the fig, and the multitude of other 
trees which, by their fruit, or by other products, yield an annual 
revenue, nature has provided Southern Europe with a partial com- 
pensation for the loss of the native forest. It is true that these 
trees, planted as most of them are at such distances as to admit 
of cultivation, or of the growth of grass among them, are but an 
inadequate substitute for the thick and shady wood; but they 
perform to a certain extent the same offices of absorption and 
transpiration, they shade the surface of the ground, they serve 
to break the force of the wind, and on many a steep declivity, 
many a bleak and barren hillside, the chestnut binds the soil 
together with its roots, and prevents tons of earth and gravel 
from washing down upon the fields and the gardens. Fruit- 
trees are not wanting, certainly, north of the Alps. The apple, 
the pear, and the prune are important in the economy both of 
man and of nature, but they are far less numerous in Switzerland 
and Northern France than are the trees I have mentioned in 
Southern Europe, both because they are in general less remu- 
nerative, and because the climate, in higher latitudes, does not 
permit the free introduction of shade trees into grounds occu- 
pied for agricultural purposes.* 
* The walnut, the chestnut, the apple, and the pear are common to the bor- 
der between the countries I have mentioned, but the range of the other trees 
is bounded by the Alps, and by a well-defined and sharply drawn line to the 
west of those mountains. From some peculiarity in the sky of Europe, culti- 
vated plants will thrive, in Northern Italy, in Southern France, and even in 
Switzerland, under a depth of shade where no crop, not even grass, worth 
harvesting, would grow in the United States with an equally high summer 
temperature. Hence the cultivation of all these trees is practicable in Europe 
to a greater extent than would be supposed reconcilable with the interests of 
agriculture. Some idea of the importance of the olive orchards may be formed 
from the fact that Sicily alone, an island scarcely exceeding 10,000 square 
miles in area, of which one-third at least is absolutely barren, has exported to 
the single port of Marseilles more than 2,000,000 pounds weight of olive-oil per 
year, for the last thirty years. 
According to Cosimo Ridolfi, Lezion? Orali, vol. ii., p. 340, in a favorable soil 
and climate the average yield of oil from poorly manured trees, which com- 
pose the great majority, is six English pounds, while with the best cultivation it 
