Vascular System
Under this name are included all those parts of plants in which true Vessels (which see) occur. As the latter are found only in flowering plants, and in Vascular Cryptogams (Ferns, Horsetails, Club-mosses, and their allies), there is no Vascular System in the remaining groups of Cryptogams, i.e., in the True Mosses, Liverworts, Algae, Lichens, and Fungi. It is often represented, or rather foreshadowed, among the Mosses and some of the species in the other groups, by bundles or strings of long, tapering cells, which, to some extent, do the same work. The Vascular System is present in the roots, stems, branches, and leaves of the Vascular Plants. It remains when continued steeping in water, or exposure to the weather, has caused the decay of all the softer cells in these plants, so that it forms the skeleton or framework on which the plants are built up. It is best seen in those parts in which the bundles or strings of which it consists are always separated by cellular tissue from one another, e.g., in leaves, and in the stems of Monocotyledons and Ferns, and in young stems of herbaceous Dicotyledons. In the stems and roots of woody Dicotyledons it becomes more difficult to recognise the true nature of the Vascular System, owing to the formation of annual rings of wood and of bast by the cambium layer just below the bark. The chief uses of the Vascular System are twofold, viz.: (1) It gives strength and mechanical support to all parts of the plant, serving as the framework for the cellular tissues, in which the work of preparing the food goes on; (2) the wood, in the Vascular System, is the channel of communication for conveying the crude sap upwards from the soil to the leaves, and the soft bast in each bundle is believed to be the chief channel by which the protoplasmic food-substances are conveyed from the leaves, in which they are prepared, to the growing points, where they are used up in forming new structures, or to the parts (tubers, seeds, &c.) where they are stored up for future use. See Sap.