100 ORGANOGRAPHY. BOOK I. 



then alike in appearance, and are both equally fm'nished with 

 stomates. In succulent leaves they are said to be either alto- 

 gether absent or very rare ; but this is not exactly the fact. 

 They are fewer and smaller, and perhaps more imperfect, in 

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

 cording to the observations of De Candolle {Organoyr. p. 272.), 

 they are, in the Orange and the Mesembryanthemum, as ten 

 in the former to one in the latter. 



T have remarked [Bot. Ttcg. 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 un- 

 der other circumstances it would have neither stomates, hairs, 

 nor elevated veins, acquires all those characters in conseqiaence 

 of its inversion. A very curious observation, in connection 

 Avith this subject, has been made by Mirbel, in his memoir 

 upon the structure of Marchantia polymorpha. 



The young bulbs' by which this plant is multiplied are ori- 

 ginally so homogeneous in structure, that there is no apparent 

 character in their organisation to show which of their faces is 

 destined to become the upper surface, and which the under. 

 For the purpose of ascertaining whether there existed any 

 natural but invisible predisposition in the two faces to undergo 

 the changes which subsequently become so apparent, and by 

 means of which their respective functions are performed, or 

 whether the tendency is given by some cause posterior to their 

 first creation, the following experiments were instituted : — 

 Five bulbs were sown upon powdered sandstone, and it was 

 foiuul that the face which touched the sandstone produced 

 roots, and the opposite face formed stomates. It was, how- 

 ever, possible that the five bulbs might have all accidentally! 



