CHAP. XIV. 
DIRECTIONS TAKEN BY ORGANS. 
409 
at the radicular end in a small green tubercle of a paler 
colour than the radicle itself. When the seed is fixed upon 
a branch by its natural glue, this incipient movement is 
effected at right angles with the branch ; the young shoot is 
then curved backwards, and the radicular extremity descends 
to the surface of the branch, to which it adheres by expanding 
into a kind of disk. From this expansion the roots are 
emitted, and penetrate the interior of the branch whereon 
the seed of the Mistletoe is fixed : its stem takes the directions 
above mentioned with reference to the centre of the branch on 
which it is fixed, and not with reference to the earth ; so that, 
with regard to the latter, it is sometimes ascending, some- 
times descending, sometimes horizontal. The same pheno- 
mena occur if the germination takes place upon dead wood 
or inorganic substances : a number of seeds were glued to the 
surface of a cannon ball; all the radicles were directed 
towards the centre of the ball. Hence it is obvious that the 
tendency of the Mistletoe is not towards the surface of its 
nutrition, but that it obeys the attraction of the body upon 
which it grows. The Mistletoe, which does not grow on the 
earth, obeys the attraction of any other body; while those 
plants which naturally grow in the earth obey no other at- 
traction than that of the earth. Parasitical Fungi, those which 
constitute mouldiness, aquatics which originate on stones, — 
all grow perpendicular to the body that produces them, and 
will therefore be placed in all kinds of positions with respect 
to the earth. 
The tendency downwards of the roots, and upwards of the 
stem, is chiefly observable in the ascending and descending 
caudex ; that is to say, in the axis of the vegetable considered 
as a whole. The lateral emissions of this axis always deviate 
from its direction in a greater or less degree : we know that 
the roots produced by the taproot, and the branches which 
proceed from the side of the principal stem, scarcely ever, 
take a direction absolutely vertical. This is probably due to 
several causes, one of which is undoubtedly the general ten- 
dency of all the parts of plants to take a direction perpen- 
dicular to the plane of the body on which they grow. The 
branches of trees are, to those which produce them, what the 
