Sec. Il. I. 4. UMBILICAL VESSELS. 2

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day and night. In regard to capillary attraétion, however high it may raife a fluid in very fmall tubes, it can not make it flow over them, as the fap-juice did in Dr. Hales’s vine-ftump; nor can it raife a fluid quite to a level with the upper rim of a glafs tube, as the fluid is there more attracted downwards by the glafs befides its gravity, and is left in confequence with a concave furface.

The means by which vegetable abforbent veflels in their living. ftate imbibe the fluids of the earth and atmofphere, and carry them forwards with fo much force, muft be fimilar to thofe, with which animal abforbent veflels perform the fame office; that is by their mouths being excited into action by the ftimulus of the fluids, which they abforb.

This circumftance is confirmed by the evident proofs of the irri- tability of plants in various other inftances, as the clofing and open- ing of the petals and calyxes of flowers by light and darknefs,warmth and cold, drynefs and moifture, and by the motions of the leaves of mimofa, or fenfitive plant, and of dionœa mufcipula, by any me- chanical fimulus. To this might be added a variety of inftances of the irritability of vegetables to the ftimulus of heat, being increafed after a previous expofure to cold, exaëtly in the fame manner as hap- pens to animal bodies, which are enumerated in a note in the Botanic Garden, Vol. I. Canto I. L 322, whence the reciprocal times of the a@ing and the ceafñng to ac of thefe vernal vegetable abforbents, which are here termed umbilical veflels, in the experiments both of Dr. Hales and Dr.Walker, may be readily explained by their having been benumbed by the cold, or excited into aétion by the warmth of the air or earth. See Sec. XII. 2. 3.

From one experiment neverthelefs of Dr. Walker’s thefe vefels occafionally aét as capillary fyphons, becaufe when he bent down a branch much lower than its origin from the tree, and cut off the end of it in the bleeding feafon, the fap flowed from the extremity of

this branch fo bent down, when fome wound$ two or three feet lbwer