CHAPTER XII. 
OF THE DIRECTIONS TAKEN BY THE ORGANS OF PLANTS. 
The substance of all that is known upon this subject has 
been combined with some excellent observations of his own 
by Dutrochet in a memoir, of which I shall avail myself 
in the following remarks : — 
"The general phenomena of nature," says this writer, "which 
are daily before our eyes, are often those which mankind con- 
siders the least attentively. Those who are unaccustomed to 
reflect upon such subjects can scarcely believe that there is 
any very extraordinary mystery in the ascent of the stems of 
vegetables, or in the descent of their roots ; and yet this is 
one of the most curious circumstances connected with vegeta- 
ble life. The downward direction of the roots may appear 
easy of explanation : it may be said that, like all other bodies, 
they have a tendency towards the centre of the earth, in 
consequence of the known laws of gravity (as is the opinion 
of Knight, in Phil. Trans, for 1806) ; but on what principle, 
then, is to be explained the upward tendency of the stem, 
which is in direct opposition to those laws ? And here lies the 
difficulty. Dodart is the first who appears to have paid atten- 
tion to this circumstance ; he pretends to explain the turning 
backwards of seeds sown in an inverted position by the fol- 
lowing hypothesis : he assumed that the root is composed of 
parts that contract by humidity ; and that the stem, on the 
contrary, contracts by dryness. For this reason, according 
to him, it ought to happen that, when a seed is sown in an 
inverted position, the radicle will turn back towards the earth, 
which is the seat of humidity ; and that the plumula, on the 
contrary, turns to the sky, or rather atmosphere, — a drier me- 
dium than the earth. The experiments of Du Hamel are well 
