appears to militate against the above hypothesis, namely, that when
two circular incisions are made, at a small distance from each other,
through the bark, round the stem of a h'ee, and the bark between
these incisions is Wholly taken away; that portion of the stem which
is below the incisions continues to live, and to increase in size, though
much more slowly than the parts above the incisions. The above-
mentioned naturalists have also observed, that a small elevated ridge
is formed round the lower lip of the wound, which makes some slight
advances to meet the bark and wood, projected in larger quantifies
from the upper lip of the wound.
Our author, in a former paper, attempted to explain the above cir- cumstance, by supposing that a small part of the true sap, descending from the leaves, escapes downwards, through the porous substance of the alburnum: in another paper he has shown, from the growth of inverted cuttings, the existence of a power in the alburnum to carry the sap in different directions; and he now describes some ex- periments made in order to show that the conclusions drawn by him are not inconsistent with the facts stated by Hales and Du Hamel; and that although the ascending sap usually rises through the al- bumum and central vessels, yet the alburnous vessels appear to be also capable of an inverted action, when such action becomes neces- sary to preserve the existence of the plant.
The first experiment described in the present paper, consisted in removing the bark by means of circular incisions at the distance of three inches from each other from the stems of several young oaks, as soon as the leaves were nearly full grown, and examining, in the succeeding winter, the state of the parts. In almost every instance the albumum was found to be lifeless, and almost dry; in one in- stance, however, it was perfectly alive; and in this the specific gra- vity of the wood, above the decorticated space, was 1114, and below it 1111, whereas the specific gravity of an unmutilated stem, from the same roots, and at the same distance from the ground, was 1112. Now if the whole of the descending, or true sap, had in the above instance stagnated above the decorticated part. the specific gravity of the wood there ought to have been much greater than it was found to be.
Mr. Knight, conceiving that he should obtain more satisfactory and decisive results from tuberous-rooted plants, now proceeded to make some experiments on the potatoe. The early varieties of this plant, as is well known, afford neither blossoms nor seeds. This cir- cumstance he attributed to the privation of nutrirnent, from the pre- tematurally early formation of the tubers; he therefore planted, in the last spring, some cuttings of a very early variety of the potatoe in garden-pots; and when the plants had grown a few inches high, they were secured to sticks, fixed erect in the pots. The mould was then washed away from the base of the stems, so that the plants were suspended in the air, and had no communication with the remaining soil, except by their fibrous roots. Efforts were soon made, by every plant, to produce runners and tuberous roots, but these were de-
