SECTE. FRS ORDENTIVESSEES. 15

a recent vegetable ftick both upwards and downwards, by fetting one end of it in a cup of water in the receiver of an air-pump, and ex- haufting the air, Veg. Stat. p. 154; whence he concludes with Grew, that thefe are air-veflels or lungs for the purpofe of refpiration, and that they receive atmofpheric air in their natural flate.

There is one objettion to their ufe as air-veffels, which is, that they have no communication with the horizontal air-veflels above de- fcribed; for by blowing forcibly through a piece of dry cane immerf- ed deep in water, no air 1s feen to bubble out of the fides, but only from the bottom of it.[t may indeed be fuppofed, that the lonoi- tudinal cavities in dry cane may not confift of the abforbent veffels above defcribed, but of the interftices between them, as the coats of thofe abforbent veflels, confifting of a fpiral line, may be thought to clofe up by their vermicular contra@tion; and their interftices, con- fifüng of vegetable cellular membrane, may be fuppofed, when dry, to become the tubes in cane. But in this cafe the longitudinal canals in dry cane Would not be circular cylinders, whereas they are fo re- prefented in a figure of a piece of cane much magnified by Dr.Grew, Tab. XX. who has in the fame figure given the mouths of hori- Zontal air-veflels of circular form and larger diameter,

But there is another infuperable objettion to this idea of their ufe, which is, that thefe veflels equally exift in the roots of plants as in their trunks; and according to Malpighi with larger diameters; and probably terminate externally only in the roots; and, as they are there not expofed to the atmofphere, they cannot ferve the purpofe of refpiration; air neverthelefs in its combined ftate, or even as dif- folved in water, may be abforbed by thefe veflels; and may appear, when the preflure of the atmofphere is removed in the exhaufted receiver; or when expanded by heat, as is feen in the froth at one end of a green ftick, when the other end is burning in the fire.

6. Thefe vesetable abforbents differ from thofe of animals in the facility, with which they carry their Auids either way; for a forked

branch