266 THE MICROSCOPICAL NEWS. 
of non-chemical molecular attraction; then may come in any in- 
fluence of atmospheric pressure whether set up by transpiration or 
otherwise ; then may come in endosmose, which is indeed probably 
itself caused by the chemical attraction between molecules of water 
and of saline matter. 
But the chemical force is static rather than dynamic, how then 
can it set up acurrent? By the attraction for each other of the 
components of tissue, on the one hand, and on the other, of those 
true compounds of water with even minute amounts of gases or 
solids which we know to exist. Tissue-compounds and waier- 
compounds meeting, ordinary chemical changes occur, force, in the 
form of heat, is absorbed, more complex compounds are built up, 
and the great bulk of the water Zer se, or, it may be, water holding 
in solution effete matters, is left to shift for itself, perhaps even 
repelled, to escape in the direction of least resistance—by transpi- 
ration in summer and by slower processes in spring. The water 
exuding from my birch-branch may be such water, a portion of the 
water that might ordinarily escape from the external surfaces of 
the wood or otherwise, with the difference that it is carrying away 
matter (sugar, etc.) not wanted just now, perhaps, but which un- 
fortunately, or, at all events, as we believe, will be wanted presently. 
The warrant for the remarks respecting the highly aqueous water- 
compounds is to be found in the known tenacity with which water 
retains traces of gases, as shown by Groves, and in the altered 
properties possessed by water when containing even traces of saline 
or other matters. Finally, whence comes the large quantity of 
chemical force or chemical attraction necessary for the binding 
together of such numbers and such amounts of substances as occur 
in the fully-formed wood of a forest tree? From the heat-force 
poured on to its leaves by the sun—force which will be re-converted 
into heat when the wood is transformed, no matter whether slowly 
by decay or quickly by combustion, into its constituent gases and 
ashes. 
It would be unwise, however, to speculate further without those 
confirmations and checks which experiment alone could afford, and 
without those safe guides which experiment alone could furnish. 
Here as elsewhere in all departments of knowledge earnest seekers 
after truth are wanted, men possessing, for this enquiry, adequate 
knowledge of physics, chemistry, and botany, and with the neces- 
sary time and means for carrying on the work. To such men 
would certainly, sooner or later, be accorded the honour of dis- 
covering, or unveiling, one more of the laws by which all nature is 
governed. ‘Then we shall know the true cause or causes of the 
movements of sap in plants.— Herts. Wat. Hist. Soc. 
