100 
ORGANOGRAPHY. 
BOOK I. 
then alike in appearance, and are both equally furnished with 
stomates. In succulent leaves they are said to be either alto- 
gether absent or vei'y rare ; but this is not exactly the fact. 
They are fewer and smaller, and perhaps jnore imperfect, in 
succulent than in other parts, but by no means absent. Ac- 
cording to the observations of De Candolle (Organo(jr. p. 272.), 
they are, in the Orange and the 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 invei ted. Thus the stomates are usually upon the under 
side of leaves, where also tlie 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 consequence 
of its inversion. A very curious observation, in connection 
with 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 
found that the face which touched the sandstone produced 
roots, and the opposite face formed stomates. It was, liow- 
ever, possible that the five bulbs might have all accidentally 
