Licence: Public Domain Mark
Credit: An introduction to botany / by John Lindley. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
56/588
![the hairs are then said to be plumose. It sometimes happens that little branchlets are produced on one side only of a hair, as on the leaves of Siegesbeckia orientalis, in which case the hair is called one-sided [secundatus]; very rarely they appear upon the articulations of the hair, which in that case is called ganglioneous. (Plate I. fig. 9. Verbascum Lychnitis): the polls en goupillon of De Candolle are referable to this form. Be- sides these, there are many other modifications. Plairs are conical, cylindrical, or moniliform, thickened slightly at the articulations (torulose), as in Lamium album, or much en- larged at the same point (nodulose), as in the calyx of Achy- ranthes lappacea. Hairs are sometimes said to be fixed by^ their middle (Plate I. fig. 10. c); a remarkable structure, common to many different genera; as Capsella, Malpighia, Indigofera, &c. This expression, however, like many others commonly used in botany, conveys a false idea of the real structure of such hairs. They are in reality formed by an elevation of one cel- lule of the cuticle above the level of the rest, and by the developement of a simple hair from its two opposite sides. Such would be more correctly named divaricating hairs. When the central cellule has an unusual size, as in Malpighia, these hairs are called poils en navette (pili Malpighiacei) by M. De Candolle ; and when the central cellule is not very apparent, poils en fausse navette (pili pseudo-Malpighiacei, biacuminati), as in Indigofera, Astragalus, Asper, See. In many plants the hairs grow in clusters, as in Malvaceae, and are occasionally united at their base : such are called stellate, and are frequently peculiar to certain natural orders. (Plate I. fig. 10. a.) All these varieties belong to one or other of the two prin- cipal kinds of hairs; viz. the Lymphatic and the Secreting. Of these, lymphatic hairs consist of tissue tapering gradually from the base to the apex; and secreting, of cellules visibly distended either at the apex or base into receptacles of fluid. Malpighiaceous and glandular hairs, stings, and those which cause asperity on the surface of any thing, belong to the latter; almost all the other varieties to the former. When hairs arise from one surface only of any of the](https://iiif.wellcomecollection.org/image/b21915714_0056.jp2/full/800%2C/0/default.jpg)
