Page:History of botany (Sachs; Garnsey).djvu/491

] lead to misconceptions respecting the movements of water in woody plants, namely that which is known as the bleeding of the wood in winter, and which depends on entirely different causes from those which produce the weeping of the vine and other woody plants in spring ; but the two things were supposed to be identical, and hence arose an unfortunate confusion of ideas. Lister indeed showed that it is possible to force water out of the wood of a portion of a branch cut from a tree in winter time by warming it artificially, and then to cause the water to be sucked in again by cooling it ; but it was reserved for a modern physiologist to prove that this phenomenon has nothing to do with the bleeding of cut stems from root-pressure, and cannot be used to explain it.

John Ray, who gave a clear and intelligent summary of all that was known respecting the nutrition of plants in the first volume of his 'Historia plantarum' (1693), also communicated some experiments made by himself on the movements of water in the wood. He follows Grew's nomenclature, who called the ascending sap in the wood lymph and the woody fibres therefore lymph-vessels, and notices particularly that the lymph especially in spring cannot be distinguished in taste or in consistence from common water. He agrees with Grew that in spring the lymph fills the true vascular tubes of the wood and oozes from them in cross sections, while in summer these are filled with air, and the lymph at that time, when there is strong transpiration in woody plants, ascends only in the lymph-vessels, that is in the fibrous elements of the wood and the bast. By suitable incisions Ray proved that the lymph can also move laterally in the wood; and by causing water to filter in opposite directions through pieces of a branch cut off at both ends, he refuted those who thought that the cavities of the wood and especially the vessels were furnished with valves to hinder the return of the lymph. But his knowledge of the mechanical causes of the movement of water in the wood was not very great.