217 
the Direction of the Growth of Roots. 
This experiment was repeated, and water was so constantly 
and abundantly given, that every part of the radicles was kept 
equally wet ; and they then became perfectly obedient to 
gravitation, without being at all influenced by the mould 
above them. 
In other experiments pieces of alum and of the sulphates of 
iron and copper were placed at small distances perpendicularly 
beneath the radicles of germinating seeds, of different species, 
to afford an opportunity of observing whether any efforts 
would be made by them to avoid poisons ; but they did not 
appear to be at all influenced, except by actual contact of the 
injurious substances. The growth of their fibrous lateral roots 
was, however, obviously accelerated, when their points ap- 
proached any considerable quantity of decomposing vegetable 
or animal matter: and when the growth of the roots was 
retarded by want of moisture, the contiguity of water, in the 
adjoining mould, though not apparently in actual contact with 
them, operated beneficially: but I had reason to suspect that 
the growth of roots was, under these circumstances, promoted 
by actual contact with the detached and fugitive particles of 
the decomposing body, and of the evaporating water. 
The growth and forms assumed by the roots of trees, of 
every species, are to a great extent, dependent upon the 
quantity of motion, which their stems and branches receive 
from winds ; for the effects of motion upon the growth of the 
root, and of the trunk and branches, which I have described 
in a former memoir, are perfectly similar.* Whatever part 
of a root is moved and bent by winds, or other causes, an in- 
creased deposition of alburnous matter upon that part soon 
* Phil. Trans. 1803, p. 7. 
MDCCCXI. 
