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said to be fibrous. In some cases, however, the vessels of the root form a thickened mass, from which the absorbent fibres diverge, and to which various names are given according to its shape and proportions; the most common varieties being the tap-root, where it descends in a tapering form into the ground, as in the Radish and Parsnip, and the tuber, in which it forms several more or less irregular, rounded masses, as in the Orchis and Potato. In the latter vegetable, however, the tuber is considered by botanists to be a modification of the stem, and not a root in the strict sense of the word. The same is the case with the leafy bulbs of the Lily and Onion, and the corm or solid bulb of the Crocus, and some other subterranean portions of plants to which the name of root is applied in common language. In this work the word is used in its popular meaning.
The stem is that portion of the plant which, rising from the root, supports the leaves and flowers. In some plants it is wanting, being represented only by the thickened rim or apex of the root from which the leaves and flower-stalks proceed, as in the Dandelion; in other instances it creeps along the ground, as in the Iris, when it is called a rhizome. The stem is in all cases formed of the vessels that descend from the leaves and flowers to the root, and in which the sap circulates, and the various juices and secretions of the plant are elaborated. In some plants it dies down every year, fresh stems rising to supply its place the following season; the plant is then termed herbaceous. In other vegetables it becomes a permanent portion of the plant, the leaf-buds continuing to send down their fibres through it as long as growth lasts, and thus producing the substance we call wood; the plant is then a tree or shrub. Whether the stem be herbaceous or permanent, the buds which produce the leaves and branches are formed at certain points on its surface called nodes, where a change of direction takes place in the fibres; the space between being termed an internode or joint.
