LIFE OF THE PLANT-CELL. 



119 



103 



nicjricans (fig. 103.), epidermis- 

 cells enlarged outwardly into 

 papilla? will be observed, al- 

 though the surface of the leaf 

 is very nearly smooth, the 

 spaces between the epidermis- 

 cells being filled up by a 

 material which extends out- 

 wardly far beyond them, is 

 readily distinguishable from 

 the cell-membrane by its op- 

 tical properties (fig. 103. c). 



When a very young leaf of 

 Hyacinthus orientalis is in- 

 spected, it will be seen to be 

 enveloped merely by a de- 

 licate epithelium, the cells of 



which are slightly elevated on the external surface in a vesicular manner- 

 During the further development of this epithelium a gelatinous matter 

 appears first in the depressions between the cells, which soon hardens, 

 and thus represents a network, the meshes of which indicate the limits 

 of the cells. In a short time the cells are wholly covered with a similar 

 layer, which is firmly united with the network above described, and 

 which, also, rapidly hardens. The epidermis-cells now secrete on their 

 external surface a material of less 

 consistence and density, which raises 

 the former layer, together with the 

 fibrous network, and gradually attains 

 considerable thickness. 



These distinct portions may be 

 observed even in the completely- 

 formed cuticle of Dipsacus fullonum 

 (fig. 104.) But in this instance the 

 epidermis- cells (c) secrete this layer, 

 not only on their external aspect (a), 

 but also secrete an intercellular sub- 

 stance on their internal aspect (b) ; 

 and in this respect the same condition 

 obtains in the layer of cells imme- 

 diately subjacent to the epidermis. 



103 A section perpendicular to the surface of the leaf of Aloe nigricans. a, Canal of 

 the stomate, filled with orange-coloured granules of resin. b, Cavity beneath the 

 stomate, surrounded by cells, containing in part chlorophyll granules (black in the 

 figure), and in part rose-red or orange-coloured resin granules. The papillary cuticu- 

 lar cells are filled with fluid of a brighter or darker red, and in part with rose-red 

 resin granules. Of the two cells forming the stomate, the one contains chlorophyll, 

 the other a single large bright-yellow granule of resin, c is the secreted layer of the 

 epidermis-cells. 



104 A section perpendicular to the surface of the leaf of Dipsacus fullonum. c, The 

 epidermis-cells, with their granular contents. , The secreted layer of the epidermis 

 cells, on their external surface. The most external portion of this secreted layer is 

 more dense, and readily distinguishable ; beneath it, and corresponding to the furrows 

 between the cuticular cells, is a fibrous network, also composed of a more dense ma- 

 terial. The epidermis-cells also secrete from their internal surface an inteicellular 

 substance, which, in this situation, joins that which is secreted by the subcuticular layer 

 of cells, which cells are again covered, on their internal aspect, with an intercellular 

 substance, resting upon the more lax green parenchyma. 



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