serves, that luxuriant shoots, which abound in sap, constantly turn
upwards, and endeavour to acquire a perpendicular direction ; but
that the feeble and more slender shoots grow in almost every direc-
tion, probably from their fibres being more dry, and their vessels less
amply supplied with sap, so that they are less afi'ected by gravitation.
To the second objection, hlr. Knight answers, that the compression
of the radicle, as it penetrates the soil, obstructs the motion of the
sap, and occasions the generation of numerous lateral roots; and as
their substance is less succulent than that of the radicle first emitted,
they are less obedient to gravitation, and consequently extend hori-
zontally in every direction. Respecting the tap-root of the oak, the
author says he has examined at least 20,000 trees of that species.
and never found one tree that possessed a tap-root; he therefore
thinks he may be allowed to doubt the existence of such a root.
Mr. Hatchett, in his former communications on this subject, gave some account of the effects produced by sulphuric acid upon turpen- tine, resin, and camphor. He now states the results of a variety of experiments made with that acid upon a great number of resins, balsams, gum-resins, and gums; from which it appears, that sul- phuric acid almost immediately dissolved the resins, forming transpa- rent brown solutions, which gradually became black; that the solu- tions of the balsams and of guaiacum were at first of a deep crimson colour, slightly inclining to brown; and that caoutchouc and elastic bitumen were not dissolved, but, after a long digestion, were only superficially carbonized.
Turpentine, common resin, elemi, tucamahaca, mastic, copaiba, copal, camphor, benzoin, the balsams of Tolu and of Peru, assafce- tida. and amber, yielded a large proportion of the tanning substance; so also did oil of turpentine.
Asphaltum yielded only a small portion of that suhstance; and some slight traces of it were obtained from gum arabic and from gum tragacanth; but none was produced from guaiacum, dragon’s blood, myrrh, gum nmmoniac, olibanum, gamboge, caoutchouc, elastic bitumen, liquorice, and manna. hir. Hatchett thinks, how- ever, that some of these would have yielded it, had not the digestion with nitric acid been too long continued.
Olive oil was partly converted into the tanning substance; so also were linseed oil, wax, and animal fat. In the experiment with linseed oil, a portion was left undissolved: this portion appeared to retain many of the properties of an inspissated fat oil. In the experiment made with wax, a white substance was obtained, which was found to possess the properties of spermaceti. In that with animal fat (in which the kidney-fat of veal was employed), a great
