410 
PHYSIOLOGY. 
BOOK II. 
Mistletoe is to the braiicli on which it vegetates : but, as there 
is a double attraction operating upon all branches, — that is to 
say, an attraction towards the stem and an attraction upwards, 
in consequence of the general law to which they all submit, — 
it results that a middle direction is taken, and, instead of a 
branch continuing to grow at right angles with some other, it 
soon abandons that direction, and points its extremity towards 
the sky. 
It has been hitherto seen, that the roots of vegetables are 
positively attracted by the body on which they grow ; it ap- 
pears, however, from the following experiment, that this 
attraction is influenced essentially by the mass of the body. 
Thus, if a seed of Mistletoe is made to vegetate on a thread, 
the radicle turns itself in all sorts of ways, and exhibits no 
signs of attraction to the thread. Dutrochet made a seed of 
Mistletoe germinate on a thread ; he then glued it upon one of 
the points of a fine needle, fixed like that of a compass, 
balancing it by a bit of wax at the other end of the needle ; 
he next placed a piece of wood at about half a line’s distance 
from the radicle ; and then covered the whole apparatus with 
a glass, placed under such conditions that it was impossible 
that any cause could move the needle. In five days the 
embryo began to bend, and direct its radicle towards the bit 
of wood, w'ithout the needle’s changing its position, although 
it was extremely movable upon its centre : in two days more 
the radicle w^as directed perpendicularly to the bit of wood, 
wdth which it had come in contact, and still the needle had 
not stirred. This proves, says Dutrochet, that the direction 
of the radicle of the Mistletoe towards a neighbouring body 
is not the immediate result of any attraction on the part of 
such a body ; but that it is the result of a spontaneous 
movement of the embryo, in consequence of the attracting 
influence exerted upon its radicle, w4iich is thus the mediate 
.or occasional cause of the phenomenon. It is obvious, indeed, 
that the inflexion of the stem of the embryo of the Mistletoe 
could not be due to the immediate attraction on the part of 
the bit of wood ; for an exterior powder sufficient to produce 
this inflexion would much more readily have produced a 
change in the direction of the needle, to one of whose points 
