THE ROOT. 7 
but the result of design. The composition of the soil varies 
singularly in different parts of the globe. In order that every 
point of the surface of the earth should be covered with vegeta- 
tion, and that no part of it should be without that incomparable 
adornment, roots must take very. varying shapes in order to 
accommodate themselves to these varieties in the composition of 
the soil. In one place the soil is hard and stony, heavy or light, 
formed of sand or clay ; in another it is dry or moist; elsewhere it 
is exposed to the heat of a burning sun, or swept, on the heights, 
by the violence of the winds and atmospheric currents; sometimes 
it is sheltered from these movements of the wind in the depth of 
some warm valley. Roots, hard and woody, separated into strong 
ramifications, yet finely divided at their terminations, are requisite 
for mountain plants, whose roots are to live in the midst of rocks 
or between the stones, in order that they may penetrate between 
the chinks of the rocks, and cling to them with sufficient force to 
resist the violence of hurricanes and other aerial tempests. Straight 
tap-roots and slightly branching plants are fit for light and per- 
meable soils. They would not suit close, clayey, and shallow soils. 
Such districts are suitable for plants whose roots stand horizontally 
just under the surface of the soil. 
These considerations are of great importance to the cultivator, 
who, if he would propagate plants successfully, must carefully 
study the nature of the soil, and choose for his experiments plants 
having roots adapted to it. 
Two modifications may be found in the two classes of roots of 
which we have been speaking. It sometimes happens that these 
roots form themselves into masses more or less voluminous, full of 
nutritive matter, which is destined to nourish the plant or to 
favour its increase. Common examples of this structure are pre- 
sented to us by the Orchis mascula of our meadows and woods, the 
Anemone, Ranunculus, and Dahlia of our flower gardens. These 
roots are called tuberous when they take the form of the roots of 
the Dahlia (Fig. 9), or tubero-fibrous when they take the form of 
those of the Orchis (Fig. 10). 
These enlargements of the root have a special use in the life of 
the plant. It is their function to accumulate, in the lower part 
of the vegetable, supplies of nutritive matter, consisting chiefly 
