EPIDERMIS. 79 



arranged irregularly round one central point, or in the case of elongated cells 

 round two eccentric points. They are often also branched, and connected by 

 anastomosis. In vertical sections they appear as thin bright radial bands. With 

 Schultze's solution they turn blue like outgrowths of the inner cellulose layer, while 

 the cuticular layers with their protruding swellings assume a brown colour. This 

 behaviour causes the doubt expressed by Nageli in these cases, as to the nature 

 of the above-mentioned slits. 



As regards the internal structure of the cuticular layers, we need not here 

 discuss the phenomena of stratification, striation, and areolation, which are general 

 for thickened cell-walls ^ Different successive layers or systems of layers (shells) 

 are in many cases cuticularised to a different extent, and are therefore of different 

 refractive power and colour differently with preparations of Iodine ; e. g. in Ilex 

 aquifolium (comp. above, Fig. 26), Aloe soccotrina, Fourcroya gigantea, Taxus 

 baccata, (Petunikow, I.e. Tab. Ill, Fig. 3, 4, 7, 9). The same holds in many cases 

 for the successive strise perpendicular to the surface. Hakea Candolleana Meisn. has 

 for instance a quite similar striation to that above described for H. ceratophylla. 

 But the strife lie in the cuticular layers, and do not extend inwards to the cellulose 

 layer: moreover they turn bright yellow with Schultze's solution, while the other 

 cuticular layers turn brown ^. Epidendron ciliare shows with Schultze's solution 

 broad strise, perpendicular to the surface, of variable and very different intensity 

 of colour. 



Another phenomenon, also of common occurrence in masses of cells, is the 

 difference in optical and chemical nature of the limiting layers, and limiting lamellce 

 of contiguous cells, from the other membranes. And this occurs often very 

 conspicuously in the cuticular layers. Sharply marked, thin limiting lamellae often 

 extend from the cuticle, tapering off inwards like wedges. They appear like 

 continuations of the cuticle inwards, between the cuticularised lateral walls of many 

 epidermal layers. They also are destroyed by those reagents, which destroy 

 cuticular substance, and therefore consist entirely or principally of it (comp. 

 Fig. 25, c. and Fig. 27). In other epidermal layers (e.g. Acer striatum, Dianthus 

 caryophyllus, &c.) limiting lamella are not visible or hardly indicated in the fresh 

 intact preparation. But in these cases also the lateral walls of contiguous cells are 

 separated by reagents, which destroy the cuticular substance, and this tends to the 

 conclusion that there is a delicate limiting lamella consisting entirely or chiefly of 

 cuticular substance. 



Ad. Brongniart^ used the term cuticle to indicate, in the first place, that superficial 

 homogeneous lamella of the Epidermis which alone remains behind when all the rest is 

 destroyed by rotting or by the action of sulphuric acid. The names of the plants 

 investigated by him show that he did not distinguish the cuticular layer from the cuticle, 

 since after the maceration both of these remain, in the leaf of Dianthus caryophyllus, as 



^ Compare Hofmeister, vol. I of this Handbook, §§ 27, 28. 



^ The striae described by Nageli, I.e. figs. 14, 15, and Schacht, Lehib. Taf. III. 27, 28, for 

 H. florida, and by von Mohl, t.c. fig. 18, for H. gibbosa, may be compared with those of H. cera- 

 tophylla. 



^ Ann. Sci. Nat. 2 ser. torn. I. p. 6-). Brongniart's first description was in the Ann. Sci. Nat. 

 I ser. torn. XXI. p. 427 (1830). 



