8o CELLULAR TISSUE. 



a connected skin, while in that of Potamogeton lucens only the cuticle remains, since the 

 cuticular layer is absent. The distinction of the two parts was not drawn by the 

 observers of the succeeding period '. Mohl first drew attention to their anatomical and 

 material difference (Bot. Zeitg. 1847, p. 499, Sec). 



As regards the cuticular layer, the view, defended earlier by himself and by Meyen, that 

 the ' cuticle ' is part of the outer membrane of the epidermal cells themselves, was dis- 

 tinctly proved in this work of Mohl : and the view held by others (Treviranus, Schleiden, 

 Grundz.), which regarded it as a product of secretory-perspiration, was laid aside. Mohl 

 says of the cuticle, ' If any one will ascribe it to a secretion from the epidermal cells, I 

 have no objection to make to this idea, still it will be difficult to afford a proof of its 

 truth.' This he confirms by the striation which occurs in many plants, from which it 

 may be concluded that there is a definite organisation, and not an origin merely from 

 hardened excreted fluid. Cohn (De cuticula, in Linnaea, Bd. 23, 1850) then gave a clear 

 statement of the case, founded especially on investigations on hairs. Wigand ^ also 

 claimed for the cuticle a (genetic) connection with the cell-membranes of the epidermis, 

 and defended his view against that of Schacht (Pflanzenzelle, Lehrbuch I), which is 

 certainly confused. Hofmeister regards it as a part of the cell membrane of the 

 epidermis '. 



If, in the face of the facts known at that time, most of which are recapitulated 

 above, the question be raised whether the cuticle consists of parts of all epidermal 

 cells, or is something distinct from these, the latter alternative must be preferred, even 

 if anatomical relations alone be regarded, and the difference of material be left on one 

 side *. Even if Payens' ' statement were confirmed, according to which the cuticle of 

 Cereus peruvianus, after continued treatment with boiling nitric acid, water, and 

 ammonia, if pressed backwards and forwards under the cover slip, separates into 

 angular pieces, each corresponding to an epidermal cell ; still this is only an isolated 

 exception. Universally in other cases the cuticle, having been first formed on the 

 embryo, while still consisting of few cells, grows over the epidermal cells, and uniformly 

 with them, retaining fundamentally its original properties. Neither in older nor in 

 younger parts can it be separated into the altered outer lamellae of single epidermal cells, 

 or groups of cells. Even if it, together with the membranes covered by it, consisted of 

 pure cellulose, it would be, anatomically considered, an independent membrane, which 

 belongs in common to the whole member or the whole plant, and must be distinguished 

 from the walls of the single cells. Its genetic relationship to the contiguous cellulose 

 layers is not thereby excluded ; it must rather be directly derived from them in all cases 

 where it grows or is renewed on a free surface, that is, in those cases where the possibility 

 of an apposition from without is excluded (e. g. such a possibility may be imagined for 

 the embryo enclosed in the embryo-sac). Further, if we neglect the embryos, pollen- 

 cells, &c., it is possible on free surfaces— in the development of the stomata — clearly to 

 observe that first the cellulose membrane alone is present, and later the cuticle appears 

 upon it. Thus, where reference can be made to the first beginnings of the development 

 of cuticle (comp. Hofmeister, /. c), at first the cellulose membrane alone is present, sub- 

 sequently it is separated into cuticle and cellulose membrane. Where the cuticle grows 

 on a free surface, the material for it can originate only from the cellulose membranes. 

 It is therefore doubtless a product of differentiation of these, and of the cells to which 

 they belong. 



» Treviranus, Physiol. I. p. 448— Meyen, Physiol. I. p. 176.— Von Mohl, Linnsea, 1842, and 

 Verm. Schiiften, p. 260, &c. 



^ Intercellularsubstanz und Cuticula. Braunschw. 1850, p. 36, &c.— Botanische Untersnchungen 

 (1854), p. 67.— Flora, 1861, p. 81, &c.— That which is said in these works of the Intercellular sub- 

 stance does not of course concern the present explanation. 



= Pflanzenzelle, p. 159, 248, 257, &c. ■> Compare Cohn, I.e. p. 382. 



° Compare Hofmeister, I.e. p. 251, 



