Caudex, a botanical term, signifying, in general, the stem, or trunk of a tree. It is properly that part of plants which joins together the plumula, or leaf, and the radicle, or root fibres; and which is called the caudex, by LinNAeUs, when applied to entire plants. He consequently divides it into the ascending and descending body of the vegetable : the former contri-butes to the formation of the trunk, the latter to that of the root. In herbs and shrubs, the caudex is denominated Caulis, or the stalk.

Dr. Darwin observes, that, in herbaceous plants, the caudex is generally a broad, flat, circular plate, from which the leaf-stems ascend into the air, and the radicles, or root-fibres, descend into the earth. Thus, the caudex of a plant of wheat lies between the stem and the radicles, at the basis of the lowermost leaf, and occasionally produces both new stems and radicles, from its sides; whereas that of a tulip is situated under the principal bulb, and generates new, though smaller ones, in the bosom of each bulb-leaf, besides one principal, or central bulb; - the caudex of the orchis, and of some species of the ranunculus, lies above their bulbous roots; but those of the buds of trees constitute the longitudinal filaments of the bark, extending from the plumula, or apex, of the bud on the branch, to the. base of it, or its root-fibres, beneath the soil.

The elongation of the caudexes, which takes place in the buds of trees, says Dr. DaRwin, is analogous to what happens to some herbaceous plants, as in wheat: when the grain is buried two or three; inches beneath the soil, an elongation of the caudex occurs almost up to the surface, where another set of fibrous roots are protruded, and the upright stem commences. It is the same with tulip-roots, and also those of many other vegetables, when planted too deep in the earth.

This caudex of the buds of trees not only descends, as before described, but likewise ascends from each bud to that above it; as on the long shoots of vines, willows, and briars; in this respect, resembling the wires of strawberries, and other creeping plants. Thus the caudex of perennial herbaceous plants consists of a broad plate, buried beneath the soil, to protect it from the frost; while that of the buds of. trees is furnished with a long, vascular cord, extending from the bud, on the branch, to the radicle, beneath the earth, and enduring the winter frosts, without injury.

When treating of vegetable generation, and the organs of reproduction, Dr. Darwin, in his "Phytologia" mentions a remarkable animal fact, illustrative of this curious, and important subject: Many insects, such as the common earth-worm, and the polypus, are said to possess so much life, throughout a great part of then-system, that they may be cut into two or more pieces, without destroying them; as each part will acquire a new head, or new tail, or both; and the insect thus become multiplied. How exactly this is resembled by the long cau-dex of the buds of trees, which possess such vegetable life, from one extremity to the other, that when the head, or plume, is lopped off, it can produce a new plume; and when the lower part is cut off, it will generate new radicles; and thus may be wonderfully •propagated. See also Bun, Bulb, and Leaves.