88 CELLULAR TISSUE. 



Sect. i8. To the cuticular structures and deposits should be appended the 

 cellulose covering, which was found by Pfitzer ' on the stems of Restio diffusus, but 

 which was absent from other allied species, and of which the development cannot 

 as yet be explained. On the outer surface of the firm large-celled, cuticularised 

 epidermis of this plant lies a colourless, almost homogeneous, and transparent, 

 brittle, dry, easily separated layer, as thick as a strong outer epidermal wall. The 

 layer does not enter the deep hollows in which the stomata fie, but it is rather 

 curved" over the opening like a bridge, and closes it with exception of a very narrow 

 longitudinal slit with toothed margin. Beneath the layer lies the cuticle : the layer 

 itself shows an exquisite cellulose reaction. According to careful investigation of 

 the unfavourable material at his disposal, Pfitzer arrives at the very probable 

 conclusion that this layer covering the cuticle is the disorganised outer layer of cells 

 of an epidermis consisting of two layers (excepting in the vicinity of the stomata) : 

 a view which is especially supported by the fact that the covering appears in surface- 

 view partitioned off by delicate lines in a cellular manner. 



Sect. 19. Dermal glands. In the cell-walls of the epidermis there occur very 

 generally distributed resins, ethereal oils, and mixtures of both; and mixed with 

 these also, though more rarely, vegetable mucilage (Bassorin, which swells greatly or 

 is dissolved in water), gum and sugar. When free these substances give to the 

 surface a sticky character ; when they are volatile they are perceived as scents. 



In contrast to the formation of wax, the occurrence of these bodies is relatively 

 seldom extended over large epidermal surfaces ; on the other hand they are usually 

 localised, partly on circumscribed spots in the level epidermis or on teeth or other 

 emergences, most commonly on hair-structures ". 



The spots on which the sticky or volatile bodies in question occur are called in 

 common speech glands, glandulcB, and the character of surface resulting from these 

 glandular, the bodies themselves the secretion, or the product of secretion, or segrega- 

 tion of the glands. But this expression is also used for other very different organs, 

 which doubtless correspond partially with those in question in the general characters 

 of the secretion, but differ widely as regards their structure. The organs of the 

 epidermis, usually termed collectively glands (with few exceptions to be treated of 

 later), are characterised by very definite anatomical properties, and should therefore 

 be designated by a definite general name, and be distinguished from the rest. They 

 may therefore be termed epidermal or dermal glands. According to the above- 

 indicated difference in the distribution and extent of the glandular properties we 

 may distinguish between glandular hair-structures {glandular hairs, scales and villi) 

 and glandular surfaces or areas {glandular surfaces, glandular spots). When the 

 latter are localised on definite emergences, it is convenient and practical to speak 

 of glandular emergences {glandular-teeth or -warts, &c.). 



The secretion of dermal glands, when it can be recognised anatomically, always 

 appears first in the walls of the cells, and gives them a peculiar structure. In most 

 cases this affects the free outer wall of the cells entirely, or partially : here there 

 appears a bladder-like swelling, hence bladder-like dermal glands. In other cases the 



> Pringsheim's Jahrb. Bd. VII. p. 564. 



' As regards the literature, the references on p. 57 should be compared. 



