EPIDERMIS. 



33 



them in other points, remain undivided, as for instance in the case represented 

 below in Fig. 29 of Klopstockia, and that cited by Pfitzer of Tradescantia zebrina; 

 or divided and undivided cells (i. e. one or several layered epidermis) stand side by 

 side in about equal quantity, as on the under side of the leaf of Passerina ericoides, 

 and the examples cited by Pfitzer of the leaf of Pittosporum Tobira, undulatum, 

 of the stem of Elegia nuda. Ephedra altissima, monostachya. The upper surface 

 of the leaf of Arbutus Unedo has two layers with their cells fitting one upon another 

 (not taking into account single cells, which remain uniseriate, and undivided), those 

 of Begonia manicata 2-3 (Pfitzer, /. c), the stem of B. tomentosa 2 ', that of Pe- 

 peromia blanda 2 ''- In the families to which the three last-named plants belong, the 

 Piperacese and Begoriiaceae, and further many species of Ficus (Fig. 18), there 

 is formed on the leaves a much stronger many-layered epidermis, which is divided 

 and developed in a much more complicated way. 



Pfitzer describes for Begonia sanguinea, ricinifolia, and peltata an epidermis of 4 to 5 

 layers, while that of B. Dregei and Fischeri on leaf and stem is simple, that In B. Dregei, 

 however, consisting of very large cells. The petiole of B. manicata has a simple epider- 

 mis, with only solitary tangentially-divided cells ; the lamina has on the upper surface 

 2-3 layers with the cells fitting one on another ; the inner of these is much higher than 

 the outer; on the under surface (Pfitzer, I.e. Taf. VI. 9) it has two layers, the cells of 

 the inner being more than double as high and broad as those of the outer — this results 

 from the fact that after the tangential division, which separates the two layers, further 

 radial division goes on in the outer, while in the inner only growth of the cells, without 

 jlivision, takes place. 

 ■ " In the Piperacese the upper surface of the leaf of all Peperomias in which the point 

 has been investigated' (P. pellucida, magnoliifolia, blanda, pereskiifolia, rubella, galioides, 

 polystachya, incana, arifolia, obtuslfolia, argyracea) is provided with an epidermis of 

 more than one layer, while that of the under side is a single layer. In P. arifolia it has 

 two, in others, e.g. P. blanda 2-4, in P. incana 7-8^ in P. pereskiifolia 15-16 layers. 

 The high number of layers, and, in those cases where the number is smaller, the con- 

 siderable size of the cells in the inner layers, giv^s to the epidermis in question a vast 

 thickness, so that it is even in P. incana thicker than the whole remaining mass of the 

 thick fleshy leaf; in P. magnoliifolia and rubella, it exceeds several-fold the rest of the 

 substance of the leaf, and in P. pereskiifolia it exceeds it seven-fold. 



According to the species the cell-division and growth either proceed simultaneously in 

 all the layers, so that all^fit with their cells one upon another; this is the case usually in 

 those with two layers, but also in the many-layered P. pereskiifolia, where only the 

 outermost layer is, as the result of divisions perpendicular to the surface, smaller-celled 

 and difl^erently arranged from the numerous inner ones (Pfitzer t.t. Taf. VI. i); or (e.g. 

 P. incana) the outer layers become smaller-celled than the inner layers, owing to numerous 

 divisions perpendicular to the surface, and the arrangement of the cells corresponds less 

 in the successive layers. 



Of the other Piperaceae a two-layered epidermis on the upper side of the leaf was 

 found by Treviranus in Chavica maculata, and by Payen in Artanthe colubrina. Miq. 



As in the Peperomias, so in many species of Ficus, the many-layered epidermis of both 

 surfaces of the leaf is produced by the division of an originally single layer. This stratum 

 . becomes smaller-celled as one proceeds from the innermost to the outermost layer. 



It has been described for F. bengalensis *, elastica, ulmifolia, pectinata, ferruginea, 



' Hildebrand, Unters. iiber d. Stamme d. Begoniaceen, p. 20, Taf. IV. 4. 

 '^ Sanio, Botan. Zeitung, 1864, p. 213. 



2 Treviranus, Verm. Schr.' IV. p. 11 ; Physiol. I. p. 449.— Pfitzer, I.e. p. 26. 

 ' Treviranus, Verm. Schr. IV. p. 11 (1821). 



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