EPIDERMIS. 



65 



are isodiametric, usually unicellular bodies ; Hairs are sac- or thread-like bodies, 

 unicellular, or consisting of a row of cells, simple or branched; Scales are flat 

 membranous structures, always consisting of many cells, arranged in one or several 

 layers ; SAaggj/ hairs are thread-like bodies, consisting of two or many layers or rows 

 of cells ; Waris and Prickles are of similar constitution, but are not thread-like, but 

 massive and hard, the warts are blunt, the prickles pointed. Intermediate forms and 

 combinations of these types are common, and may of course be easily named 

 after them. 



• On each hair-structure may be distinguished the body and the foot. The former 

 is the part which protrudes outwards above the epidermal surface. The foot is the 

 part which lies within this ; it is rarely similar in form to the epidermal cells, especially 

 often it exceeds them in height, as it not uncommonly extends inwards far beyond 

 the inner surface of the epidermis, into the sub-epidermal tissue. 



The epidermal cells, which surround the foot, may resemble those not bordering 

 on a hair ; very often they are quite different from these, and may then be termed 

 subsidiary cells of the hair. Of the various forms of these, that of an annular or 

 rosette-like girdle of subsidiary cells surrounding the foot of the hair recurs especially 

 often (Fig. 21 .ff). 



Around the foot of many hairs, or below it, the subepidermal tissue, covered by 

 the epidermis, bulges outwards, so that the foot is borne by an emergence of that . 

 tissue. This may be limited to a slight excrescence, upon which, as its ' bulbus,' the 

 hair is seated, or to a small, stalk-like outgrowth, which in multiseriate shaggy hairs 

 is with difBculty distinguished from the hair itself; but, on the other hand, it 

 may attain considerable dimensions, as in the prickles of Dipsacus^ and species 

 of Solanum, &c., which bear a hair on their apex, or the fringed scales of Begonia 

 manicata^ 



The converse condition of the origin of a hair, in a more or less deeply hollowed 

 depression of the surface, is not less common. 



Small hairs do not always overtop the edge of the depression in which they 

 stand. They fill it completely, or only partially, as those on the leaves of the 

 Pleurothallidese (Pleurothallis, Stelis, Physosiphon, Nephelaphyllum, Octomeria), 

 which (comp. page 54) were wrongly described by Meyen as cavities of the 

 Epidermis. 



The direction of the body of the hair, as regards the surface which bears it, 

 varies extremely between that at right angles and that parallel to it. 



The hair-structures of one and the same surface are in the minority of cases all 

 alike, if slight individual differences be disregarded. As examples may be named 

 all known cases of Root-hairs, Leaf of Elseagnese, Bromeliace^, Leaf and stem of 

 Convolvulus Cneorum, &c. Much more commonly one and the same surface bears 

 hairs of different properties, two to five sorts often occurring close to one another. 

 Comp. Fig. 31. 



If we disregard the root-hairs, which with very few exceptions (Elodea, Lemna, 

 Opbioglosseffi) are universally distributed, and reproductive organs, which are not to 



' ScMeiden, Grundz. 3 Aufl. I. p. iSi. 



» Compare Weiss, in Schr. d. zoolog. bot. Vereius. Wien, 1858. 



