302 
REMARKS ON SOME VEGETABLE PHENOMENA. 
tical man, and who, in accounting for the cause, always attributed the 
incident to the autumnal descent of the sap ; others have supposed it 
to be caused by the descent of fibrous processes from the superior buds. 
Both these ideas have been partly objected to. Relative to the first, it 
has been averred that no enlargement of any part of a plant happening 
in the months of May or June, can possibly be caused by the'descent of sap 
in autumn; and to the second it has been objected, that the healing of 
a wound at the base of a lofty tree, sixty or seventy feet below any 
active bud, cannot be healed by processes produced by buds so far above 
the wound. 
That the sap of a tree is diffusible in all directions, has never been, 
nor cannot be denied; but that there is any general subsidence in 
the autumn, after the growth ceases, is extremely problematical. If there 
be any descent of either sap or physical member (and that there is 
something of the kind , is perfectly evident ), it must begin to descend at 
the commencement of the summer growth, and continue till it ends. 
From what has been stated, two or three questions naturally occur, 
viz., which constituent of the plant is it that has a tendency to sink 
rather than to be distended vertically or laterally ? Has the action of 
the atmosphere any effect on the ordinarv development of vegetable 
membrane ? Can the induction of the food of plants, either from the 
earth or atmosphere, have any influence in impelling the development? 
To these questions a few words by way of answer may be given. 
To the first it may be replied, that the vital membrane is the only 
constituent possessing susceptibility of change; and which is spontane¬ 
ously mutable under the external influences of heat, light, and moisture. 
This membrane is exceedingly delicate and colourless before it is 
formed into wood or bark. When exposed to the air and light, it 
becomes incrusted by a film, which in time becomes the bark. This 
hardening of the exterior is always in proportion to the degrees of light 
and heat falling thereon: of course the more exposed parts are sooner and 
more thickly incrusted than the sheltered parts ; and hence the lower 
edges of the exposed membrane are protruded downwards with more 
celerity than the more exposed parts. Whether as a body, or when 
projected in fibrous processes, the direction is invariably downward to 
gain darkness and moisture. These last observations answer the second 
question in so far as relates to the vital membrane and roots of trees; 
but which is directly contrary to the vertical tendencies of the stems of 
the same. 
The third question refers to whether or not the nutriment received 
at either extremity affects the expansion in an opposite direction : in 
other words, does the nourishment received by roots accelerate the 
upward growth ; and is there any reason to believe that food imbibed 
