BOTANY FOR YOUNG PEOPLE AND COMMON SCHOOLS
How Plants Grow
A Simple Introduction to Structural Botany
by Asa Gray
Originally published in 1858 and now in the public domain.
HOW PLANTS GROW, AND WHAT THEIR PARTS OR ORGANS ARE.
SECTION IV. -- Different Forms or Kinds of Roots, Stems, and Leaves (page 1 of 3).
81. The Organs of Vegetation, or those that have to do with the life and growth of a plant, are only three, Root, Stem, and Leaf.
And the plan upon which plants are made is simple enough. So simple and so few are the kinds of parts that one would hardly expect plants to exhibit the almost endless and ever-pleasing diversity they do. This diversity is owing to the wonderful variety of forms under which, without losing their proper nature, each of these three organs may appear.
82. The study of the different shapes and appearances which the same organ takes in different plants, or in different parts of the same plant, comparing them with one another, is called Morphology and is one of the most interesting parts of Botany.
But in this book for young beginners, we have only room to notice the commonest forms, and those very briefly, although sufficiently to enable students to study all common plants and understand botanical descriptions. Those who would learn more of the structure and morphology of plants should study the Lessons in Botany.
§ 1. Of Roots.
83. The Root is the simplest and least diversified of the three organs. Yet it exhibits some striking variations.
84. As to origin, there is the primary or original root, formed from the embryo as it grows from the seed, and the branches it makes. Annuals, biennials, and many trees are apt to have only such roots.
But when any portion of their stems is covered by the soil, it makes secondary roots. These are roots which spring from the sides of the stem. Every one knows that most stems may be made to strike root when so covered and having the darkness and moisture which are generally needful for roots.
Perennial herbs and most shrubs strike root naturally in this way under ground. All the roots of plants raised from tubers, rootstocks, and the like (74-76), are of this sort, and also of plants raised from slips or cuttings. In warm and damp climates there are likewise many
85. Aerial Roots, namely, roots which strike from the stem in the open air.
In summer we often find them springing from the joints of the stalks of Indian Corn, several inches above the soil. Some of these reach the ground and help to feed the plant.
In the famous Banyan-tree of India aerial roots on a larger scale strike from the spreading branches, high up in the air, grow down to the ground and into it, and so make props or additional trunks. Growing in this way, there is no limit to the extent of the branches, and a single Banyan will spread over several acres of ground and have hundreds of trunks all made from aerial roots.
87. Air-Plants. Roots which never reach the ground are also produced by certain plants whose seeds, lodged upon the boughs or trunks of trees, high up in the air, grow there, and make an Epiphyte, as it is called (from two Greek words meaning a plant on a plant), or an Air-Plant.
The latter name refers to the plant's getting its living altogether from the air, as it must, for it has no connection with the ground at any time. And if these plants can live on air, in this way, it is easy to understand that common vegetables get part of what they live on directly from the air. In warm countries there are many very handsome and curious air-plants of the Orchis family. A great number are cultivated in hot-houses, merely fixed upon pieces of wood and hung up. They take no nourishment from the boughs of the tree they happen to grow upon.
88. Parasitic Plants are those which strike their roots, or what answer to roots, into the bark or wood of the species they grow on, and feed upon its sap.
The Mistletoe is a woody parasitic plant, which engrafts itself when it springs from the seed upon the branches of Oaks, Hickories, or other trees.
The Dodder is a common parasitic herb, consisting of orange-color or whitish stems, looking like threads of yarn. These coil round the stalks of other plants, fasten themselves by little suckers in place of roots, and feed upon their juices. Living as such a plant does by robbing other plants of their prepared food, it has no leaves of its own, except little scales in their place, and has no need of any.
89. Shapes and Uses of Roots. Common roots, however, grow in the soil. And their use is to absorb moisture and other matters from the soil, and sometimes to hold prepared food until it is wanted for use, as was explained in the last section (70, 73). Those for absorbing are
Fibrous roots, namely, slender and thread-shaped, as in Fig. 48, 56, and generally branching. Very slender roots of the sort, or their branches, are called Rootlets; and these do most of the absorbing. The roots of annuals are mostly fibrous, as they have nothing to do but to absorb; and so are the smaller branches of the roots of shrubs, trees, and other plants.
Fleshy roots are those of herbs which form a thick and stout body, from having much nourishment deposited in them. They belong particularly to biennial herbs (69), and to many perennials (73). Some sorts have names according to their shapes. The root is a
Tap-root, when of one main body, and tapering downwards to a point; as that of a Carrot (Fig. 71), and of a seedling Oak (Fig. 41). And a tap-root is
Conical, when stout, and tapering gradually from the upper end to a point below; as a carrot (Fig. 71), parsnip, or beet.
Spindle-shaped, when thicker in the middle, and tapering upwards as well as downwards, like a radish (Fig. 57); and
Turnip-shaped, or Napiform, when wider than long, or with a suddenly tapering tip, as a turnip (Fig. 70). Roots are
Clustered or Fascicled when, instead of one main root, there are several or many of about the same size; as in Indian Corn (Fig. 48), and other grain (Fig. 56). Here the clustered roots are fibrous, being for absorbing only. When such roots, or some of them, are thick and fleshy, as they are when used as storehouses of food, they become Tuberous. The roots of the Dahlia, for instance (Fig. 58), are clustered and tuberous, or tuber-like.
2. Of Stems. CLICK HERE
3. Of Leaves. CLICK HERE
Analysis of the Section.
81. Vegetation very simple in plan, very diversified in particulars. 82. The study of the forms of the organs is Morphology.
83-89. Roots, their forms and kinds. 84. Primary or original; secondary, how they originate. 85. Aerial roots. 86. Aerial rootlets. 87. Air-Plants, how they live. 88. Parasitic Plants, their economy. 89. Shapes of roots: fibrous; fleshy, the principal sorts.