390 



STRUCTURE OF PHANEROGAMIC PLANTS. 



species formed to exist in tropical climates. A very curious 

 modification of the cuticle is presented by the RocTiea falcata, 

 commonly known as the "ice-plant;" a designation it owes to 



FIG. 183. 



FIG. 184. 



Portion of the Cuticle of the upper surface of the leaf of Moehea falcata, as seen at A from its inner 

 side, and at B from its outer side: a, a, small cells forming the inner layer of the cuticle; b, 6, large 

 prominent cells of the outer layer; c, c, stomata, disposed between the latter. 



the peculiar appearance of its surface, which looks as if it were 

 covered with frozen dewdrops. This appearance is occasioned 

 by the presence of a layer of very large oval cells (Figs. 183, 184, 



b, b), which lie detached one 

 from another upon the surface 

 of the ordinary cuticle, a, a. 

 In other instances, the cuticle 

 is partially invested by a layer 

 of scales, which are nothing 

 else than flattened cells, often 

 having a very peculiar form ; 

 whilst in numerous cases, 

 again, we find the surface be- 

 set with hairs, which occasion- 

 ally consist of single elongated 

 cells, but are more commonly 

 made up of a linear series, 

 attached end to end, as in Fig. 

 153. Sometimes these hairs 



bear little glandular bodies at their extremities, by the secretion 

 of which a peculiar viscidity is given to the surface of the leaf, as in 

 the Sundew (Drosera) ; in other instances, the hair has a glandular 

 body at its base, with whose secretion it is moistened ; so that 

 when this secretion is of an irritating quality, as in the Nettle, it 

 constitutes a " sting." A great variety of such organs may be 

 found, by a microscopic examination of the surface of the leaves 

 of Plants having any kind of superficial investment to the cuticle. 

 Many connecting links are found between hairs and scales, such 

 as the "stellate hairs" of the Deutzia scabra, which a good deal 

 resemble those within the air-chambers of the Yellow Water-lily 

 (Fig. 152). 



Portion of a vertical section of the same Leaf, 

 showing the small cells, a, a, of the inner layer of 

 cuticle; the large cells, 6, 6, of the outer layer; c, 

 one of the stomata; <2, d, cells of the parenchyma; 

 L, lacuna between the parenchymatous cells, into 

 which the stoma opens. 



