CHAP, ii.] of Plants. Ray. 471 



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 con- 

 sistence 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. 



