Читать книгу Field and Woodland Plants - William S. Furneaux - Страница 6

Table of Contents

The root is that portion of the plant which descends into the soil for the absorption of the mineral food required. It really serves a double purpose, for, in addition to the function just mentioned, it fixes the plant in its place, thus forming a basis of support for the stem and its appendages.

Forms of Roots

1. Simple fibrous. 2. Branched fibrous. 3. Tap root. 4. Tuberous root.

Roots are capable of absorbing liquids only, and all fertile soils contain more or less soluble mineral matter which is dissolved by the moisture present. This matter is absorbed mainly by the minute root-hairs—outgrowths of the superficial cells—which are to be found on the rootlets or small branches that are given off from the main descending axis.

The principal forms of roots occurring in our flowering plants are:—

1. The simple fibrous root, consisting of unbranched fibres such as we see in the Bulbous Buttercup and the Common Daisy.

2. The branched fibrous root, as that of the Chickweed and Grasses.

3. The tap root, which is thick above and tapers downwards, like the roots of the Dandelion, Carrot and Wild Parsnip.

4. The tuberous root, common among the Orchids.

5. The creeping root, possessed by some Grasses in addition to their fibrous roots.

Besides these common forms there are roots of a somewhat exceptional character, such as the aerial roots or suckers which grow from the stem of the Ivy and serve to support the plant; and the roots of the Mistletoe, which, instead of penetrating the soil, force their way into the substance of certain trees, from which they derive the necessary nourishment.

The student of plant life must always be careful to distinguish between roots and underground stems, for there are many examples of creeping and tuberous stems which resemble certain roots in general appearance. A true root bears no buds, and, therefore, is not capable of producing new plants. If a root creeps under the ground, as does the root of the Barley Grass, it merely serves the purpose of collecting nourishment from a wider area—a matter of considerable importance when the soil is dry and deficient in suitable mineral food. A creeping stem, on the other hand, developes buds as it proceeds, each bud giving rise to a new plant; and the creeping itself is the result of the growth of a permanent terminal bud.

Again, when studying plants for the purpose of identification, it is often important to note whether the root is annual, biennial, or perennial; that is, whether the root lives for one season only, lives throughout the winter, and supports the plant for a second season, or retains its life for an indefinite number of years.

Most of the roots that live over one season are of a fleshy nature, thick and tapering, or tuberous, and contain more or less stored nourishment which assists the new growths that are called forth by the warmth and light of the early spring sun.