CHAPTER VII

THE ROOT--THE FORMS OF ROOTS

=The Root System.=--The offices of the root are _to hold the plant in place_, and _to gather food_. Not all the food materials, however, are gathered by the roots.

[Illustration: FIG. 32.--TAP-ROOT SYSTEM OF ALFALFA.]

[Illustration: FIG. 33.--TAP-ROOT OF THE DANDELION.]

The entire mass of roots of any plant is called its =root system=. The root system may be annual, biennial or perennial, herbaceous or woody, deep or shallow, large or small.

=Kinds of Roots.=--A strong leading central root, which runs directly downwards, is a =tap-root=. The tap-root forms an axis from which the side roots may branch. The side or spreading roots are usually smaller. Plants that have such a root system are said to be _tap-rooted_. Examples are red clover, alfalfa, beet, turnip, radish, burdock, dandelion, hickory (Figs. 32, 33).

A =fibrous root system= is one that is composed of many nearly equal slender branches. The greater number of plants have fibrous roots. Examples are many common grasses, wheat, oats, corn. The buttercup in Fig. 34 has a fibrous root system. Many trees have a strong tap-root when very young, but after a while it ceases to extend strongly and the side roots develop until finally the tap-root character disappears.

[Illustration: FIG. 34.--A BUTTERCUP PLANT, with fibrous roots.]

=Shape and Extent of the Root System.=--The depth to which roots extend depends on the _kind of plant_, and the _nature of the soil_. Of most plants the roots extend far _in all directions_ and lie comparatively _near the surface_. The roots usually radiate from a common point just beneath the surface of the ground.

_The roots grow here and there in search of food_, often extending much farther in all directions than the spread of the top of the plant. Roots tend to spread farther in poor soil than in rich soil, for the same size of plant. _The root has no such definite form as the stem has._ Roots are usually very crooked, because they are constantly turned aside by obstacles. Examine roots in stony soil.

_The extent of root surface is usually very large_, for the feeding roots are fine and very numerous. An ordinary plant of Indian corn may have a total length of root (measured as if the roots were placed end to end) of several hundred feet.

The fine feeding roots are _most abundant in the richest part of the soil_. They are attracted by the food materials. Roots often will completely surround a bone or other morsel. When roots of trees are exposed, observe that most of them are horizontal and lie near the top of the ground. Some roots, as of willows, extend far _in search of water_. They often run into wells and drains, and into the margins of creeks and ponds. Grow plants in a long narrow box, in one end of which the soil is kept very dry and in the other moist: observe where the roots grow.

=Buttresses.=--With the increase in diameter, the upper roots often protrude above the ground and become _bracing buttresses_. These buttresses are usually largest in trees which always have been exposed to strong winds (Fig. 35). Because of growth and thickening, the roots elevate part of their diameter, and the washing away of the soil makes them to appear as if having risen out of the ground.

[Illustration: FIG. 35.--THE BRACING BASE OF A FIELD PINE.]

=Aërial Roots.=--Although roots usually grow underground, _there are some that naturally grow above ground_. These usually occur on climbing plants, the roots becoming _supports_ or fulfilling the office of tendrils. These aërial roots _usually turn away from the light_, and therefore enter the crevices and dark places of the wall or tree over which the plant climbs. The trumpet creeper (Fig. 36), true or English ivy, and poison ivy climb by means of roots.

[Illustration: FIG. 36.--AËRIAL ROOTS OF TRUMPET CREEPER OR TECOMA.]

[Illustration: FIG. 37.--AËRIAL ROOTS OF AN ORCHID.]

In some plants all the roots are aërial; that is, _the plant grows above ground_, and the roots gather food from the air. Such plants usually grow on trees. They are known as _epiphytes_ or _air-plants_. The most familiar examples are some of the tropical orchids, which are grown in glass-houses (Fig. 37). Rootlike organs of dodder and other parasites are discussed in a future chapter.

Some plants bear aërial roots, that may _propagate the plant_ or may _act as braces_. They are often called =prop-roots=. The roots of Indian corn are familiar (Fig. 38). Many ficus trees, as the banyan of India, send out roots from their branches; when these roots reach the ground they take hold and become great trunks, thus spreading the top of the parent tree over large areas. The muscadine grape of the Southern states often sends down roots from its stems. The mangrove tree of the tropics grows along seashores and sends down roots from the overhanging branches (and from the fruits) into the shallow water, and thereby gradually marches into the sea. The tangled mass behind catches the drift, and soil is formed.

[Illustration: FIG. 38.--INDIAN CORN, showing the brace roots at _oo_.]

=Adventitious Roots.=--Sometimes roots grow from the stem or other unusual places as the result of some accident to the plant, being located without known method or law. They are called =adventitious= (chance) =roots=. Cuttings of the stems of roses, figs, geraniums, and other plants, when planted, send out adventitious roots and form new plants. The ordinary roots, or soil roots, are of course not classed as adventitious roots. The adventitious roots arise on occasion, and not as a normal or regular course in the growth of the plant.

=No two roots are alike=; that is, they vary among themselves as stems and leaves do. _Each kind of plant has its own form or habit of root_ (Fig. 39). Carefully wash away the soil from the roots of any two related plants, as oats and wheat, and note the differences in size, depth, direction, mode of branching, number of fibrils, color, and other features. The character of the root system often governs the treatment that the farmer should give the soil in which the plant or crop grows.

[Illustration: FIG. 39.--ROOTS OF BARLEY AT _A_ AND CORN AT _B_.

Carefully trace the differences.]

Roots differ not only in their form and habit, but also in color of tissue, character of bark or rind, and other features. It is excellent practice to _try to identify different plants by means of their roots_. Let each pupil bring to school two plants with the roots very carefully dug up, as cotton, corn, potato, bean, wheat, rye, timothy, pumpkin, clover, sweet pea, raspberry, strawberry, or other common plants.

=Root Systems of Weeds.=--Some weeds are pestiferous because they seed abundantly, and others because their underground parts run deep or far and are persistent. Make out the root systems in the six worst weeds in your locality.