6o TIMBER AND SOME OF ITS DISEASES, [chap. 



on the structure and functions of timber turn up by 

 the way during the discussion. It is true, the subject 

 demands the combined efforts of the physicist and the 

 botanist for its complete treatment, but it has seemed 

 possible to give a general account of the whole con- 

 troversy, without necessarily entering into those side 

 issues which turn upon the more purely physical and 

 mathematical points. With respect to the importance 

 of the subject to the physiologist there is no need to 

 say more than that it has points of contact and sugges- 

 tion with almost every department of that vast study. 



In and about the year i860, much light had been 

 thrown on the subject of capillarity, and, for our 

 purposes, especially by the researches of Jamin,^ who 

 thought he could show that the ascent of water in 

 a tree was simply a capillary phenomenon, the 

 vessels &c. in the stem being the capillary tubes 

 concerned. 



If a capillary glass tube is placed with one end in 

 water, the surface of the column which rises in the 

 tube is concave, as is well known, owing to the adhesion 

 between the glass and the water : the concave surface 

 may be regarded as a film, which exerts pressure on 

 the interior of the liquid, but which pressure is smaller 

 than it would be if the film were plane. Hence the 



1 See, for instance, Comptes Rendus, 1860, t. 1. pp. 172, 311, 385. 



