EPIDERMIS. 



93 



they do occur, as in the parenchyma of Ferns (Sect. 53). The distinction of dermal 

 glands from the latter is therefore in any case necessary. It may even be retained, if it 

 be preferred to attach to the term gland a different meaning from our present one. 



The anatomical peculiarity of the glandular parts of the epidermis consists in the 

 appearance in the cell-iuall of that body, which is termed the secretion of the gland, as a 

 part sharply defined from the cellulose layers. The wall grows in thickness at the 

 glandular spot, by intercalation of a layer between its outer and inner side. The 

 intercalated mass differs in material from the cellulose- and cuticular-wall, and is termed 

 a secretion. These are the appearances directly visible. More careful investigations 

 are necessary to answer the question as to the appearance and origin of the secretion. 

 But in any case it is incorrect to imagine a ' perspiration ' in the sense of a passage of 

 large optically determinable masses formed in the interior of the glandular cells through 

 the membrane. Where it is possible accurately to observe glands with resinous secretion 

 intact, during their most intense secretion, as I can state, e. g. for the glandular hairs of 

 Aspidium, Cistus, Pelargonium, Molucella, Pogostemon, Primula sinensis, and also for the 

 depressed glands of Psoralea, and for Rhododendron, there is to be found within the 

 cell-wall clear cell-sap, and remarkably homogeneous or very uniform finely granular 

 protoplasm, and no trace of optically visible drops of resin, the presence of which is 

 assumed in the ordinary perspiratory theory. Hanstein's description of the visible 

 passage of previously formed drops of resin through the cell- wall (e.g. in Viola, /. c.) 

 therefore appears to me to be much in need of confirmation, in so far as it applies to 

 glandular hairs which have not begun to wither. Existing observations rather favour the 

 view, that the secretion — at all events the resinous secretion — is, like wax, first deposited 

 in the wall itself, and perhaps is first formed in the wall, although it must be allowed 

 that the material for its formation is and must be derived primarily from the protoplasm 

 of the glandular cells, or of some other cell. In the interior of old glandular cells, in 

 which the secretory activity has ceased, or is ceasing, larger collections of the (resinous) 

 secretion certainly do appear. Further investigation must decide what is the cause of 

 this phenomenon, which diflfers from the original and undoubtedly normal condition. 

 According to the view derived from conditions which we have termed normal, the 

 secretion found in the old glandular cells might have originated in the wall, and have 

 passed from this into the interior of the cell. 



Of the two main forms of glands above distinguished according to the point in the cell 

 where the secretion is formed, the bladder-like glands are by far the most widely 

 distributed; and of these again the various series of glandular hairs, scales, and •villi. 

 The structure characteristic of these was first cleariy figured, but not understood, by 

 Meyen (Secretionsorgane, Taf. I, Fig. 30, d) for the small glandular scales of Melissa 

 ofiicinalis. In 1854 J. Personne gave a very good description and figure of the glandular 

 scales of the Hop (Ann. Sci. Nat. 4 Ser. I, p. 299), which for a long time were not 

 understood : in 1856 Unger figured the structure of the glandular scales of Plectranthus 

 fruticosus (Anat. und Physiol, p. 212), and later (Grundlinien, p. 82) the glandular villi of 

 Cannabis: A. Weiss gave (Pflanzenhaare, I.e., Figs. 258, 279 and 280, 310, 343, 364) a 

 number of clear figures of glandular hairs, without rightly seeing the state of the case. 

 Hanstein (Bot. Ztg. 1868, p. 697, &c.) first authenticated the characteristic structure for 

 a large series of cases, and recently Rauter and Martinet followed him (/. c, comp. p. 57). 

 From the facts hitherto known, the general conclusion, here repeated, may be directly 

 drawn, that the glandular or non-glandular structure is connected with no definite form 

 or articulation of hair-structures. It should be specially asserted for hairs and villi, that 

 capitate forms should not be identified or confused with glandular. There are glandular 

 hairs which are not capitate (Cistus): the hairs of the 'mealy' leaves of the Cheno- 

 podiacese are exquisitely capitate, but not glandular, &c. It is true, however, that the 

 majority of glandular hairs are also capitate, and that the glandular structure is localised 

 on the head; conversely also only the minority of the capitate hairs are not glandular. 

 A tolerably detailed review of the different forms in question cannot at present be given. 



