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.