STRUCTURE OF CUTICLE AND LEAVES. 



419 



in the Oleander, the Cuticle of which, when separated, has an 

 almost leathery firmness. This difference in conformation is 

 obviously adapted to the conditions of growth under which these 

 Plants respectively exist ; since the Cuticle of a plant indigenous 

 to Temperate climates, would not afford a sufficient protection to 

 the interior structure against the rays of a Tropical sun ; whilst 

 the diminished heat of this country would scarcely overcome the 

 resistance presented by the dense and non-conducting tegument of 

 a species formed to exist in Tropical climates. 



310. A very curious modification of the Cuticle is presented by 

 the Rochea falcata, which has the surface of its ordinary cuticle 

 (Figs. 224, 225, a, a) nearly covered with a layer of large pro- 

 minent isolated cells, b, b. A somewhat similar structure is found 

 in the Mesembryanthemum, crystallinum, commonly known as the 

 Ice-Plant ; a designation it owes to the peculiar appearance of its 

 surface, which looks as if it were covered with frozen dewdrops. 

 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 beset with Hairs, which occasionally consist of single 

 elongated cells, but are more commonly made up of a linear series, 

 attached end to end, as in Fig. 202. 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 Grland- 



Fig. 224. 



Portion of the Cuticle of the upper surface of the Leaf of Rochea 

 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, b, large prominent Cells of the outer layer ; c, c, Stomata dis- 

 posed between the latter. 



ular 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 



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