s afford; and that Polonian secret of
the liquor of the walnut-tree root; with an encouragement of more
frequent experiments to educe saccharine substances upon these
occasions: But the book being publish'd so long since this _Discourse_
was first printed, I take only here the liberty to refer the reader to
one of the best entertainments in the world.

But now before we expatiate farther concerning saps; it is by some
controverted, whether this exhaustion would not be an extreme detriment
to the growth, substance, and other parts of trees: As to the growth and
bulk, if what I have observ'd of a birch, which has for very many years
been perforated at the usual season, (besides the scars made in the
bark) it still thrives, and is grown to a prodigious substance, the
species consider'd. What it would effect in other trees (the vine
excepted unseasonably launc'd) I know not: But this calls to mind, a
tryal of Esq; Brotherton, (mentioning some excortications and incisions,
by what he observ'd in pruning,) that most (if not all) of the sap
ascends by the lignous part of trees, not the cortical; nor between the
cortical and lignous: And that the increase of a tree's growth in
thickness, is by the descent of the sap, and not by the ascent; so as if
there were no descent, the tree would increase very little, if at all;
for that there is a perpetual circulation of the sap, during the whole
Summer; and whilst it is in this course, and not a descent at Michaelmas
only, as some hold, but evaporated by the branches, during Summer and
Autumn, and at Spring supplied with rains. He also thinks it probable,
that the bodies of plants, as well as those of animals, are nourish'd
and increas'd by a double _pabulum_ or food; as water and air both
impregnated, mixing and coalescing by a mutual conversion.

That all plants and animals seem to have a two-fold kind of roots, one
spreading into the earth, the other shooting up into the air; which, as
they receive and carry up their proper nutriments to the body of the
plant and root, so they carry off the useless dregs and recrements, &c.
But this curious note seeming fitter to have been plac'd in our chapter
of Pruning, (upon which this learned gentleman has given us his
experience) I beg pardon for this diverticle, and return to my subject.

4. But whilst the second edition was under my hand, there came to me
divers papers upon this subject, experimentally made by a worthy friend
of mine, a le