256 POSITION OF STOMATES. [BOOK i. 



vesicles of the subjacent parenchym are filled with the green 

 substance which determines the colour of the leaf. The epi- 

 dermis is not always formed of a single layer of vesicles, but 

 in some cases consists of two, or even three. No trace is 

 discoverable of vessels either terminating in or beneath the 

 cuticle ; Brongniart states this most explicitly, and my own 

 observations are in accordance with his : an opinion, there- 

 fore, which some botanists have entertained, that spiral ves- 

 sels terminate in the stomates (D. C. Organogr. p. 27*2. &c.), 

 must be abandoned. At the margin of a leaf the epidermis 

 is generally harder than elsewhere, and sometimes becomes 

 so indurated as to assume a flinty texture, as in the Sedges, 

 and many other plants. 



Stomates are found upon various parts of the epidermis : 

 in some plants only on that of the under side of leaves, in 

 others on the upper also ; in floating leaves upon the latter 

 only. When leaves are so turned that their margins are 

 directed towards the earth and the heavens, the two faces 

 are then alike in appearance, and are both equally furnished 

 with stomates. In succulent leaves they are said to be either 

 altogether absent or very rare ; but this is not exactly the 

 fact. They are fewer and smaller, and perhaps more imper- 

 fect, in succulent than in other parts, but by no means absent. 

 According to the observations of De Candolle (Organogr., 

 p. 272.), they are, in the Orange and Mesembryanthemum, 

 as ten in the former to one in the latter. 



I have remarked (Bot. Reg. 1540.) the singular fact, that 

 certain plants have the power of forming stomates on the 

 upper surface of their leaves, if from any cause their leaves 

 are inverted. Thus the stomates are usually upon the under 

 side of leaves, where also the veins are more prominent, and 

 hairs appear exclusively, if hairs are found upon only one of 

 the two surfaces. In Alstromeria that side of the leaves 

 which is organically the undermost becomes, in consequence 

 of a twist in the petiole, the uppermost, and that side which 

 is born uppermost is turned undermost ; and then the organic 

 underside, being turned uppermost, has no stomates ; while 

 the organic upper side, being turned downwards, although 

 under other circumstances it would have neither stomates, 



