EPIDERMIS. 65 



has been already said. The shape of their body repeats that of all single hair-forms, 

 from which it differs only by its articulation — being pluri- or multiseriate. It terminates 

 in a head, or is simply conical, or resembles a tufted hair ; the latter for instance in the 

 shaggy h:.irs of the leaves of Leontodon hastilis and incanus, which fork at their ends into 

 2-5 stiff conical hairs, in the shaggy hairs of the above-cited species of Solanum, Croton, 

 and Correa (p. 62), and the Melastomeae, where they end in a rich tuft of hairs ; to these 

 may be added Osbeckia canescens, and Medinilla farinosa. Its lateral margin is smooth, 

 or toothed and zigzagged by the outgrowth of conically elongated cells ; e. g. the conical 

 shaggy hairs of the Hieracia, species of Papaver, and Mimosa ; or it even bears tufts of 

 hair (Correa speciosa). In shaggy hairs the foot is very often seated on an emergence. 

 Compare e. g, the capitate glandular shaggy hairs of the leaves of Ribes (Hanstein, 

 Rauter, Martinet, /. c). The family of the Melastomaceae has unusually numerous forms 

 of shaggy hairs with the most various transitions to scales and tufted hairs. 



IV. In the simplest case Bladders differ from unicellular hairs only in form, and 

 might be called by the same name, were it not too contradictory to the original meaning 

 of the word to call a spherical body a hair. Such unicellular round bladders, with a 

 broad foot penetrating far below the epidermis, or borne by an emergence, are known on 

 the foliage-leaf of Mesembryanthemum crystallinum, Tetragonia expansa and echinata, 

 and Oxalis carnosa \ On the whole leaf-surface of Rochea falcata ^ and longifolia 

 cylindrical tough bladders rounded at the top arise between the small epidermal cells ; 

 they are provided, above their broad foot, with several blunt outgrowths, which almost 

 touch the epidermal surface. They are all of the same height, and are in close juxta- 

 position, so as to form an almost complete covering of the epidermis. In R. coccinea 

 the margin alone is fringed by a single row of such bladders, which are rather elongated 

 to the form of a short thick hair. 



The herbaceous stem, petiole, and under surface of the leaf of many Piperaceae — 

 Piper nigrum Hort, Enkea glaucescens, Artanthe elongata — are often but not always 

 covered in the young but almost fully unfolded state by scattered spherical bladders, as 

 large. as a pin's head, which shine like transparent pearls. These prove to be unicellular 

 hair-structures, with a very small foot inserted in the epidermal surface, or projecting 

 further inwards. On older parts they burst, and dry up to inconspicuous black-brown 

 specks. Besides these there occur in the same epidermis very numerous hair-cells, 

 which only differ from the large bladders by their small foot-cell protruding above the 

 outer surface as an inconspicuous papilla : it may therefore be said that many hairs re- 

 main inconspicuously small, while the minority swell to form the transparent bladders. 



Just the same appearance for the naked eye, with the same transitory nature, is seen 

 in the round or oval bladders, as large as a millet seed, which Meyen ^ discovered in 

 Begonia plantanifolia, vitifolia, Cecropia palmata, peltata, Pourouma guianensis, Urtica 

 macrostachys, in all cases distributed as above in Piper : further in Bauhinia anatomica, 

 especially on the stem when several years old. These he named pearl-glands. Such 

 structures are often observed also on Vitis, Ampelopsis* (A. quinquefolia, Veitschii), 

 Cissus velutina, also on Pleroma macrantha (Melastomaceae). These pearl-bladders 

 (those of Pleroma have not been investigated) coincide with those mentioned for Piper in 

 this point, that they are chiefly composed of very large bladder-like cells, which are thin- 

 walled, and contain, besides radially-striated protoplasm, much watery fluid, and a number 

 of brilliant colourless globules of resin or oil. In other points their structure differs. In 

 the Begonias, according to Meyen, they are hair-structures which are allied to capitate 

 shaggy hairs. The body of the pearl consists of about a dozen cells of the above 



' Meyen, Secrelionsorg. Tab. VII. figs. 8-16, 38, 39. — Weiss, I.e. 



^ K. Sprengel, Anleit. z. Kennt. d. Gew. 2 Aufl. I. p. 113, Taf. III. — A. Brongniart, Ann. Sci. 

 Nat. I Ser. XXI. p. 453, Taf. 10. 



' Secretionsorgane, p. 45, Taf. VII. * Hofmeister, Handb. Bd. I. p. 545. 



