MODERN GEOGRAPHY EMBRACES ORGANIC LIFE. ay ( 
The rushing waters sweep down earth from the uplands ; in 
the first moment of repose, vegetation seeks to reéstablish itself 
on the bared surface, and, by the slow deposit of its decaying 
products, to raise again the soil which the torrent had lowered. 
So important an element of reconstruction is this, that it has 
been seriously questioned whether, upon the whole, vegetation 
does not contribute as much to elevate, as the waters to depress, 
the level of the surface. 
Whenever man has transported a plant from its native 
habitat to a new soil, he has introduced anew geographical 
force to act upon it, and this generally at the expense of some 
indigenous growth which the foreign vegetable has supplanted. 
The new and the old plants are rarely the equivalents of each 
other, and the substitution of an exotic for a native tree, shrub, 
or grass, increases or diminishes the relative importance of the 
vegetable element in the geography of the country to which it 
is removed. Further, man sows that he may reap. The pro- 
ducts of agricultural industry are not suffered to rot upon the 
ground, and thus raise it by an annual stratum of new mould. 
They are gathered, transported to greater or less distances, and 
after they have served their uses in human economy, they 
enter, on the final decomposition of their elements, into new 
combinations, and are only in small proportion returned to the 
soil on which they grew. The roots of the grasses, and of 
many other cultivated plants, however, usually remain and 
decay in the earth, and contribute to raise its surface, though 
certainly not in the same degree as the forest. 
The smaller vegetables which have taken the place of trees 
unquestionably perform many of the same functions. They 
radiate heat, they absorb gases, and exhale uncombined gases 
and watery vapor, and consequently act upon the chemical con- 
stitution and hygrometrical condition of the air, their roots pene- 
trate the earth to greater depths than is commonly supposed, and 
form an inextricable labyrinth of filaments which bind the soil 
together and prevent its erosion by water. The broad-leaved 
annuals and perennials, too, shade the ground, and prevent the 
