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who has civen a fioure of them, which is copied in Plate I. His. of this work. Very fine horizontal perforations through the bark of trees are alfo mentioned by Duhamel, which he believes to be per- fpiratory or excretory organs, but adds, that there are others of much Jarger diameter, fome round and fome oval, and which in the birch- tree ftand prominent, and pierce the cuticle or exterior bark. Phy- fique des arbres, T, 1. T'ab. III. Fiss8and.1r:|

Thefe veflels probably contain air during the living flate ofthe tree, as they pierce the external bark, which frequently confifts of many doubles, like a roll of linen cloth; as a new cuticle is annually pro- duced beneath the old one, like a new{carf-fkin beneath à blifter in animal bodies; and the old one fometimes continues, and fometimes peels off like the cuticle of a ferpent, as is feen on the trunks of many cherry-trees and birches. Thefe veflels, when contracted in dry tim- ber, appear like horizontal infertions in many planed boards, in which the fpiral abforbent veflels become by their contraction the lon- gitudinal fibres, as appears in the figure of a walking cane given by Dr. Grew, Tab. XX.

Thefe horizontal vefels I fuppofe to contain air inclofed in a thin moift membrane, which may ferve the purpofe of oxygenating the fluid in the extremities of fome fine arteries of the embryon buds, in the fame manner as the air at the broad end of the egg is believed to Oxygenate the fluids in the terminations ofthe placental veffels of the embryon chick, as further noticed in Sect. LIL 2. 6. and IIL 1. 4

5. The abforbent veflels of trees in pafing down their trunks confift of long hollow cylinders, whofe fides I believe to be compofed of a fpiral line, and are of fuch large diameters in fome vecetables as to be vifible to the naked eye, when they become dry and empty, as in Cane. Air Will rapidly paf through thefe veffels in either direction, as may be feen in hgbting a cane fome inches long at either end, and drawing the fmoke through the pores of it into the mouth, as through a tobacco-pipe, Dr, Hales readily pafled both air and water through

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