66 



MOKPHOLOGY OF THE CELL. 



of the reagents. According to de Barj-,' the cuticle merely 

 covers the pure soft cellulose membrane of the epidermal cells 

 when these are thin-walled ; but when the walls are thicker, 

 especially in epidermis which is long-lived, that part of the cell- 

 wall which borders on the cuticle becomes infiltrated with cutin, 

 and thus there arise one or more layers of modified cellulose, 



each of which exhibits the reac- 

 tions of cutin. When such cells are 

 treated with warm potassic hydrate 

 (a ten per cent solution is, on the 

 whole, strong enough), the cutin is 

 slowlj- removed, and the cellulose 

 wall remains, although with con- 

 siderable loss of substance. Walls 

 which are thus impregnated with 

 cutin in strata form cuticularized 

 layers? The management of a 

 warm solution of potassic hydrate, 

 in order to obtain satisfactorj' re- 

 sults in the demonstration of the 

 fine stratification, demands much 

 care. It is advisable to appl^- very 

 gradual increments of heat to the 

 glass slide in the case of the more 

 delicate specimens. 



225. Waxy and resinous matters 



are frequently associated with the 



cuticle. In some cases the amount 



of such substances is large, and assumes commercial importance. 



The young leaves of the wax palm (Ceroxylon andicola) are said 



1 Vergleichende Anatomie, p. 80. 



2 This division into apparent lamellse can lie easily demonstrated in some 

 cases by the application of cliloroiodide of zinc, which imparts a yellowish 

 color to the thick film, except at its outer surface. Mohl explained the struc- 

 ture of the exposed cell-wall in Viscuni album, where the film is very thick, 

 as follows : "The epidermis cells consist here of two or three generations 

 enclosed one within another, of which all the thickened walls on the outer 

 side have become blended together into a membrane composing the cuticle. 

 These layers are to be called the outicular layers of the epidermis, to dis- 

 tinguish them from the mass secreted on the outside of the cells, the true 



Fig 46. Transverse section of the leaf of Aloe verrucosa: a, section in water, — the' 

 non-cuticularized parts of tlie membranes shaded; above these are the cuticular 

 layers covered by the cuticle proper ; 6, section heated in potassic hydrate ; the cuticle 

 proper has been raised from the cuticularized layers; c. section boiled in potassic hy- 

 drate; cuticle proper removed, epidermal cells separated, outicular layers distinguished 

 by finer stratlllcatian. 



