life of the tree is out of the earth; and this
upward motion has a mechanical power in pushing on the growth. "_Forced
onward_ by the current of sap, the plumule ascends," (Lindley, p.
132,)--this blood of the tree having to supply, exactly as our own blood
has, not only the forming powers of substance, but a continual evaporation,
"approximately seventeen times more than that of the human body," while the
force of motion in the sap "is {50} sometimes five times greater than that
which impels the blood in the crural artery of the horse."

18. Hence generally, I think we may conclude thus much,--that at every pore
of its surface, under ground and above, the plant in the spring absorbs
moisture, which instantly disperses itself through its whole system "by
means of some permeable quality of the membranes of the cellular tissue
invisible to our eyes even by the most powerful glasses" (p. 326); that in
this way subjected to the vital power of the tree, it becomes sap, properly
so called, which passes downwards through this cellular tissue, slowly and
secretly; and then upwards, through the great vessels of the tree,
violently, stretching out the supple twigs of it as yon see a flaccid
waterpipe swell and move when the cock is turned to fill it. And the tree
becomes literally a fountain, of which the springing streamlets are clothed
with new-woven garments of green tissue, and of which the silver spray
stays in the sky,--a spray, now, of leaves.

19. That is the gist of the matter; and a very wonderful gist it is, to my
mind. The secret and subtle descent--the violent and exulting resilience of
the tree's blood,--what guides it?--what compels? The creature has no heart
to beat like ours; one cannot take refuge from the mystery in a 'muscular
contraction.' Fountain without supply--playing by its own force, for ever
rising and falling all through the days of Spring, spending itself at last
in gathered clouds of leaves, and iris of blossom.

Very wonderful; and it seems, for the present, that {51} we know nothing
whatever about its causes;--nay, the strangeness of the reversed arterial
and vein motion, without a heart, does not seem to strike anybody. Perhaps,
however, it may interest you, as I observe it does the botanists, to know
that the cellular tissue through which the motion is effected is called
Parenchym, and the woody tissue, Bothrenchym; and that Parenchym is
divided, by a system of nomenclature which "has some advan