392 



STRUCTURE OF PHANEROGAMIC PLANTS. 



chantia (214). 



Fig. 18 



Portion of the Cuticle of the leaf of the Iris 

 germanica, torn from its surface, 'and carryinj^ 

 away with it a portion of the pareiichymjitous 

 layer in immediate contact with it: — a, a, elon- 

 gated cells of the cuticle ; b, b, cells of the stomatn ; 

 c, c, cells of the parenchyma; d, d. impressions 

 formed by their contact, on the epidermic cells; 

 e. e, lacunffi in the parenchyma, corresponding to 

 the stomata. 



Stomata are usually found most abundantly (and 

 sometimes exclusively) in the 

 cuticle of the lower surfaces of 

 leaves, where they open into the 

 air-chambers that are left in the 

 parenchyma which lies next the 

 inferior cuticle ; in leaves which 

 float on the surface of water, 

 however, they are found in the 

 cuticle of the upper surface 

 only ; whilst, in leaves that ha- 

 bitually live entirely submerged, 

 as there is no distinct cuticle, 

 so there are no stomata. In the 

 erect leaves of Grasses, the Iris 

 tribe, &c., they are found equally 

 (or nearly so) on both surfaces. 

 As a general fact, they are least 

 numerous in succulent Plants, 

 whose moisture, obtained in a 

 scanty supply, is destined to he 

 retained in the system; whilst 

 they abound most in those which exhale fluid most readily, and 

 therefore absorb it most quicklj^ It has been estimated that no 

 fewer than 160,000 are contained in every square inch of the 

 under surface of the leaves oi Hydrangea and of several other 

 plants ; the greatest number seeming always to present itself in 

 species, the upper surface of whose leaves is entirely destitute of 

 these organs. In Iris germanica, each surface has nearly 12,000 

 stomatain every square inch ; and in Yucca, each surface has 40,000. 

 In Oleander, Banhsia, and some other plants, the stomata do not 

 open directly upon the lower surface of the cuticle, but lie in the 

 deepest part of little pits or depressions which are excavated in 

 it, and which are lined with hairs ; the mouths of these pits, with 

 the hairs that line them, are well brought into view by taking a 

 thin slice from the surface of the cuticle with a sharp knife ; but 

 the form of the cavities, and the position of the stomata, can only 

 be well made out in vertical sections of the leaves. 



249. The internal structure of Leaves is best brought into 

 view by making vertical sections, that shall traverse the two 

 layers of cuticle and the intermediate cellular parenchyma; por- 

 tions of such sections are shown in Figs. 184, 186, and 187. In 

 close apposition with the cells of the upper cuticle (Fig. 186, a, 

 a), which may or may not be perforated with stomata [c, c, d, i), 

 wefind a layer of soft thin-walled cells, containing a large quantity 

 of chlorophyll; these cells usually press so closely against one 

 another, that their sides become mutually flattened, and_ no 

 spaces are left, save where there is a definite air-chamber into 

 which the stoma opens (Fig. 184, l); and the compactness of 



