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.
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.
Fig. 35.—The Bracing Base of a Field Pine.
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.