1886-87.] Movement of Water in Plants. 95 



were placed on the upper surface. He was able to place 

 a considerable weight on the upper surface without producing 

 subsidence of the epidermis cells. From this he calculated 

 that a whole leaf could lift 180 kg. a short distance. This 

 is the only attempt at exact measurement of this force that 

 I know, but if we consider the number of living cells that a 

 vessel encounters on its course from the root to the leaf, we 

 must consider it as probably the most important agent in the 

 ascent of water. 



Capillarity would be, according to Scheit (4), able to raise 

 the water to a height of 1'25 to 1'69 m. Vesque (13) gives, 

 on the other hand, ten metres. But there are three distinct 

 theories as to the contents of the vessels and tracheids, which 

 would modify the action of capillarity. First, Scheit holds 

 that the vessels are full of water-vapour during the day, and 

 at night contain water. Secondly, Vesque (13) and Elfving 

 (10) hold that the vessels contain air-bubbles, which are 

 suspended in water (not touching the sides of the vessels). 

 Thirdly, Boehm holds that the air-bubbles are in contact 

 with the sides of the vessels. Taking Scheit's view first, 

 it must be remembered that the main loss of water occurs 

 during the day. Van Tieghem (26) gives the loss of water 

 by the evaporation due to the action of chlorophyll 

 " chlorovaporisation " as 168 g. to every 2 g. produced by 

 the ordinary evaporation, which takes place both day and 

 night. If we imagine a vessel filled during the night w^ith 

 water, and suppose that as the water evaporates, the empty 

 space is filled with water- vapour, there is no difficulty in 

 seeing that the process of emptying can go on, the 

 continuity from the leaf to the root being kept up by tlie 

 water-vapour ; but the difficulty consists in seeing how the 

 vessel is fiUed up with water at night, and here Scheit gives 

 no assistance, and we are obliged to take capillarity and 

 root-pressure alone, and these two forces appear to be 

 insufficient. 



Secondly, if the air-bubbles are supposed to be floating 

 freely in a vessel full of water, and if we suppose that 

 capillarity can raise a column of water to a height of 10 

 metres, and that the amount of air is equal to the amount 

 of water, then in this vessel capillarity can raise the water 

 to a height of 20 metres, because the water is exactly half 



