PLATE 11
Multicellular Uniseriate Branched Hairs
1. Mullen leaf (Verbascum thapsus, L.).
2. Lavender flowers (Lavandula vera, D. C.).
3. Dittany of Crete (Origanum dictamnus, L.).
The lavender hairs (Plate 11, Fig. 2) have mostly opposite branches, and the walls are rough. Thus the multicellular branched hairs may be divided into subgroups which have alternate, opposite, whorled, or in certain hairs irregularly arranged branches. Each class may be again subdivided according to color, character of cell termination, etc., as cited at the beginning of the chapter.
Occasionally multicellular hairs assume the form of a shield (Plate 12, Fig. 1); in such cases the hair is termed peltate, as in the non-glandular multicellular hair of shepherdia canadensis.
Hairs grow out from the surface of the epidermis in a perpendicular, a parallel, or in an oblique direction. Hairs which grow parallel or oblique to the surface are usually curved, and the outer curved part of the wall is usually thicker than the inner curved wall.
The mature hairs of some plants consist of dead cells. In other plants the cells forming the hair are living. When dried, those hairs, which were dead before drying, contain air; while those hairs which were living before drying, show great variation in color and in the nature of the cell contents. The contents are either organic or inorganic. The commonest organic constituent is dried protoplasm. In cannabis indica are deposits of calcium carbonate.
Multicellular multiseriate branched hairs are the ultimate division of the pappus of erigeron, aromatic goldenrod, arnica, grindelia, boneset, and life-everlasting.
The hairs of erigeron (Plate 13, Figs. 1 and 2) are slender; the walls are porous. Each hair terminates in two cells, which are greatly extended and sharp-pointed; the branches from the basal part of the hairs (Plate 13, Fig. 1) are of about the same length as the apical branches.
The hairs of aromatic goldenrod (Plate 13, Figs. 3 and 4) are larger than those of erigeron; the diameter is greater and the walls are non-porous. The apex of the hair terminates in a group of about four cells of unequal length, which are sharp-pointed. The branches of the basal cells (Plate 13, Fig. 3) are similar to the branches of the apical cells.
The hairs of arnica (Plate 14, Figs. 1 and 2) have thick, strongly porous walls; the branches terminate in sharp points. The apex of the hair terminates in a single cell. The basal branches (Plate 14, Fig. 2) are much longer than special branches.