90 Mr G. F. Scott Elliot on the [sess. lt. 



On the Movement of Wafer in Plants. By G. F. Scott 

 Elliot, M.A., B.Sc 



(Read 14tli July 1887.) 



There has been more discussion on the subject of the 

 ascent of crude sap in the living plant than on almost any 

 other botanical problem, and the literature is correspondingly 

 large. I have intentionally confined myself to the more 

 recent observations, and I have to thank Professor Dickson, 

 Dr Macfarlane, and Mr John Eattray for the very kind 

 assistance they have given me in this respect. 



The question naturally falls under two heads. First, the 

 path by which the sap ascends ; and, secondly, the moving- 

 causes. The first of these questions is regarded by most 

 German and French botanists as practically decided, but as 

 Mr Vines (1), in his recent work on the physiology of 

 plants, has dismissed their view in small type of a short 

 paragraph, it may be of service to bring some of the evidence 

 together. 



The older view of Sachs (2) and linger that the water 

 travels i7i the lualls of the lignified vessels, and not in their 

 cavities, rests mainly on the supposed fact that these vessels 

 contain air and not water. It was for exactly the same 

 reason that arteries were long supposed to conduct air and not 

 blood; and there seems to be as little foundation in both 

 cases. Von Hohnel (3) showed long ago that the cavities of 

 the vessels were not in communication with the intercellular 

 spaces or stomata. Moreover, the same observer, as well as 

 Scheit (4), Boehni (5), and Russow * (6), have shown that cell- 

 walls, when wet, are practically impervious to air. Scheit (4), 

 for instance, was unable, even with a pressure of 120 cm. of 

 mercury, to expel air from a piece of the stem of Abies 

 halsamea.f There is no evidence to show that the air can 

 enter by the roots. There is therefore some difficulty in 

 understanding how the air can enter the vessels except 

 accidentally. 



Sachs lays stress on the fact that freshly-cut wood floats 



* See also Weisner, SUz. d. k. Akad. d. Winn., A1)t. i., 1879; Schwendener, 

 Schutz-ichf/idcn, I'eilin, 1882. 



t Klebiiliii's (7) experiments can only be held to prove tlie existence of air 

 in intercellular spaces. 



