CIRRUS, or CIRRHUS, in Botany, a clasper or tendrill; that fine spiral string or fibre put out from the footstalks, by which some plants, as the ivy and vine, fasten themselves to walls, pales, or trees for support. The term is synonymous to the capreolus, clavícula, and viticulus of other botanists; and is ranked by Linnaeus among the fulcra, or parts of plants that serve for protection, support, and defence.

Tendrils are sometimes placed opposite to the leaves, as in the vine; sometimes at the side of the footstalk of the leaf, as in the passion flower; and sometimes, as in winged pea, pisum ochrus, they are emitted from the leaves themselves. With respect to composition, they are either simple, that is, composed of one fibre or chord, as in the vetch; or compound, that is, consist of two, three, or more, as in the everlasting pea. Bitter-sweet, folium dulcamara, bignonia, and ivy, send forth tendrils which plant themselves like roots in the adjacent walls, or the bark of the neighbouring trees. Claspers, says the ingenious Dr Grew, are like trunk-roots, a mean betwixt a root and a trunk, but a compound of both, as may be gathered from their circumvolutions, in which they mutually ascend and descend. In the mounting of the trunk, continues the same author, claspers serve for support. Thus, in vines, the branches being very long, fragile, and slender, would be liable to frequent breaking, unless, by means of their claspers, they were mutually contained together; so that the whole care is divided betwixt the gardener and nature: the former with his ligaments of leather, secures the main branches; and nature, with those of her own providing, secures the lefs. Their aptitude to this end is seen in their convolutions, a motion not proper to any other part; and also in their toughness, which is so much the more remarkable, as they are slenderer than the branches from which they proceed. In the trailing of the trunk, tendrils serve for habilement and shade: thus, in cucumbers the trunk and branches being long and fragile, would be driven to and fro by the winds, to the great prejudice of both themselves and their tender fruits, were they not, by these ligaments, held fast together, and preserved in association and good fellowship. The same claspers serve likewise for shade, so that a natural abour is formed by the branches of the cucumber, in the same manner as an artificial one is made by tangling together the branches of trees; for the branches, by the linking of the claspers, being couched together, the tender fruits lie under the umbrage of a bower made of their own leaves. Most of the pea-bloom flowers have twining claspers, that is, which wind to the right and back again.