Page:An introduction to physiological and systematical botany (1st edition).djvu/75

 Rh stalks and leaves, no doubt by tubes or vessels on purpose. Finally, it is observable that all plants, as far as any experiment has been made, contain a common fluid, which at certain seasons of the year is to be obtained in great quantity, as from vine branches by wounding them in the spring before the leaves appear, and this is properly called the sap. It is really the blood of the plant, by which its whole body is nourished, and from which the peculiar secretions are made.

The great difficulty has been to ascertain the vessels in which the sap runs. Two of the most distinguished inquirers into the subject, Malpighi and Grew, believed the woody fibres, which make so large a part of the vegetable body, and give it consistence and strength, to be the sap-vessels, analogous to the blood-vessels of animals, and their opinion was adopted by Du Hamel. In support of this theory it was justly observed that these fibres are very numerous and strong, running longitudinally, often situated with great uniformity (an argument for their great importance), and found in all parts of a plant, although in some they are so delicate as to be