PECULIAR ADAPTATIONS. OLEANDER. 165 



upper. The cells of that part are themselves of a shade fully as 

 deep ; but a much smaller number of them lie against the trans- 

 parent colourless cuticle. This may be easily seen, by cutting a 

 thin slice from the under side of the leaf with a sharp knife, in 

 such a manner as to detach a portion of the cuticle with the cells 

 adherent to it; and on magnifying this it will be observed, how 

 small a proportion of it is really rendered green, by the coloured 

 tissue in contact with it. The large amount of air which these 

 passages contain, is made evident, by putting a leaf in water 

 under the receiver of an air-pump ; and if the pressure be re- 

 moved from above, by exhausting the air, a number of minute 

 bubbles will be seen to issue from the pores of the leaf, forming 

 a portion of the air previously contained in it. 



249. Nearly all the leaves which assume the ordinary posi- 

 tion, having one surface directed upwards and the other down- 

 wards, closely correspond with the one just adduced as an ex- 

 ample in their general structure. There are, however, some 

 curious exceptions. Not unfrequently we find the openings of 

 many of the stomata extremely minute, or even entirely blocked 

 up ; especially in plants which inhabit hot and dry situations, 

 and in which, therefore, less superfluous moisture has to be ex- 

 haled through them. It is in such that we find the cuticle 

 formed of more than a simple row of cells. The Oleander is a 

 very remarkable example of this structure. The upper cuticle 

 consists of three rows of cells ; and beneath this, we find two 

 layers of green cells, packed with extreme regularity and close- 

 ness, so as not to leave any passages between them ; but between 

 these and the lower cuticle, the texture of the parenchyma is 

 very loose. The lower cuticle contains three, and sometimes 

 four, layers of cells ; and its exterior is covered with downy 

 hairs. In its substance we find cavities, opening externally by 

 a small orifice, and closely lined within by similar delicate hairs; 

 and amongst these hairs, are situated extremely minute stomata. 

 Now, as already mentioned, it seems that these hairs act as so 

 many little rootlets ; absorbing moisture with which they may 

 be in contact, when the necessities of the plant require it ; and 

 nothing can more effectually aid them, than the little cavities 



