392 



STRUCTURE OF PHANEROGAMIC PLANTS. 



chantia (214). 



FIG. 185 



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 



Portion of the Cuticle of the leaf of the Iris *> .-, p -, nl 



germanica, torn from its surface, and carrying tribe, &C., they are tOUttd equally 



away with it a portion of the parenchymatous (or nearly SO) Oil both SUrfaCCS. 



layer in immediate contact with it: a, a, elon- A o-Anm-fll fopf fhmr avA looaf 



gated cellsofthecuticle;M,cellsofthestomata; ^ S ^ g 61161 ? 1 Iact > e J "J 



c, c, cells of the parenchyma; d, d. impressions UUmerOUS 111 SUCCUlent .Plants, 



formed by their contact, on the epidermic cells; w ] lose moisture, obtained in a 



e. e, lacunae in the parenchyma, corresponding to , . ' -, . -, , 



the stomata. scanty supply, is destined to be 



retained in the system ; whilst 



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

 therefore absorb it most quickly. It has been estimated that no 

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

 under surface of the leaves of 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 

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

 In Oleander, Banksia, 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], which may or may not be perforated with stomata (c, c, d, d), 

 we find 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 



