In other hairs the division wall is horizontal; this produces a chain of superimposed secreting cells, as in some of the glandular hairs of belladonna leaf (Plate 61, Fig. 1), etc.
In other hairs the division walls are both vertical and horizontal, as in tobacco (Plate 61, Fig. 4), henbane (Plate 61, Fig. 3), belladonna (Plate 61, Fig. 1).
Other characters to be kept in mind in studying glandular hairs are the following: Color of cell contents; size of the cells, whether uniform or variable; character of wall, whether smooth or rough.
SECRETION CAVITIES
Secretion cavities are divided into three groups, according to the nature of the origin of the cavity: first, schizogenous cavities, which originate by a separation of the walls of the secretion cells; secondly, lysigenous cavities, which arise by the dissolution of the walls of centrally located secretion cells; and thirdly, schizo-lysigenous cavities, which originate schizogenously, but later become lysigenous owing to the dissolution of the outer layers of the secretion cells.
PLATE 61
Stalked Glandular Hairs
1. Belladonna leaf (Atropa belladonna, L.).
2. Geranium stem (Geranium maculatum, L.).
3. Henbane leaf (Hyoscyamus niger, L.).
4. Tobacco leaf (Nicotiana tabacum, L.).
SCHIZOGENOUS CAVITIES
Schizogenous cavities occur in white pine bark (Plate 62, Fig. B). The cells lining the cavity are mostly tangentially elongated, and the wall extends into the cavity in the form of a papillate projection. Immediately back from these cells are two or three layers of cells which resemble cortical parenchyma cells, except that they are smaller and their walls are thinner.