EPIDERMIS. 5, 



Capitate hairs occur on most leaf-forming plants, especially Dicotyledons and Ferns 

 as a rule in company with non-glandular hairs. It is true they are absent from many 

 large groups ; e. g. (all ?) Graminese, Cyperacea:, Palms, most Cruciferae. To this category 

 belong in the first place the great majority of the universally distributed glandular hairs : 

 in our consideration of these we shall have to betake ourselves to single examples 

 (Sect. 19). Meanwhile we need only remark here, that the glandular hairs are 

 characterised by no special form, but rather by definite properties of the cell walls • 

 therefore the terms capitate and glandular hair are not equivalent. In the case of many 

 capitate hairs, it is as yet uncertain whether they possess the characteristic properties of 

 glandular hairs, since in the investigation of them no attention was paid to the 

 fundamental point, and since their external development shows no difference from 

 that of glandular hairs. Such cases may therefore remain unnoticed here, and only a few 

 typical examples be cited of non-glandular capitate hairs. The family of the Cheno- 

 podiaceae furnishes the longest series of these: they are short hairs with a uni- or 

 pluricellular cylindrical basal portion, which acts as stalk, and bears a relatively large 

 bladder-like apical cell, usually of a round shape, but often irregular. They occur 

 scattered on the leaf of many species of Chenopodium and Atriplex (e.g. Ch. album, 

 Quinoa, Atriplex hortensis '), especially while these parts are young : later the bladder- 

 like terminal cells are easily detached, and then together form a friable 'meal.' In 

 other ChenopodiacesE, whose leaves have a permanently white or gray surface, these 

 hairs are so closely packed that their terminal cells (which dry up on mature parts) touch 

 and overlap one another, forming a continuous layer over the epidermis, which does not 

 fall off, e. g. Obione portulacoides, Atriplex rosea, A. nummularia. Hort. 



Non-glandular capitate hairs occur elsewhere, e. g. on the leaf of the Pelargoniums. 

 The petiole of Pelargonium zonale shows side by side five sorts of hair ; two are sharply 

 conical (comp. above, p. 61), the one more delicate, without septa, the other stronger 

 and with one septum ; besides these there are three sorts of capitate hairs, (a) glandular 

 with short, usually 2-3 celled stalk, and large unicellular, globular, glandular head^; {b) 

 short-stalked, with inclined, obliquely obovate terminal cell, perhaps also glandular ; and 

 (c) elongated hairs bearing on a usually three-celled stalk a large oval or pear-shaped 

 head-cell, not glandular (comp. Weiss, I. c. Fig. 367). Non-glandular capitate hairs with 

 a short 1-2 celled stalk, and a globular head composed of two cells standing perpendicularly 

 side by side, are very common among the Labiatae, together with glands and conical 

 hairs. On the whole, they seem to occur very often as inconspicuous structures. 



II. Scales. Of the flat outgrowths of epidermis composed of one or few layers of 

 cells, two forms may be distinguished, those which are scutiform, and those which are 

 attached laterally. 



The former consist of a short stalk or foot, standing perpendicular to the epidermal 

 surface, and a more or less round, umbrella-like disk, attached by its middle to the stalk. 

 This is usually so short that the disk lies almost on the epidermis. It is either wholly a 

 hair-structure, unicellular (e. g. Oleaceae) or pluricellular ; or is formed, at its insertion, 

 from a small emergence ; or (Shepherdia and other Elaeagnese) it is wholly an emergence, 

 i. e. the round scale is seated at its centre directly upon a short emergence. The scale 

 itself consists of radially arranged cells or rows of cells, which arise by corresponding 

 divisions (i. e. arranged, as regards the hair, radially and perpendicularly). The number 

 of these varies greatly, from four (Jasminum) to very many. In scales where the 

 number is large the arrangement is often irregular, especially at the centre, by reason of 

 tangential divisions, which appear in addition to the radial ones. At the periphery the 

 cells usually grow out radially like hairs, so that delicate stellate shapes are produced. 



It is obvious from what has been said that the more simple forms of this category can 

 hardly be distinguished from stellate hairs, such as those of Polypodium lingua (Fig. 21, 



' Meyen, Secretionsorgane, Taf. II. fig. i; Weiss, I.e. p. 559, fig. 198. 

 ' Hanstein, /. c. p. 745 . 



