106 COMPENDIUM OF GENERAL BOIANT. 



experiments concerning osmosis, I shall offer the following explan- 

 atory statements : 



1. Capillarity cannot replace the molecules of water removed 

 by evaporation from the periphery of a tree. In a capillary system 

 one meter in height in which the possil^le height of the column of 

 water is lifty meters, according to the diameter of the interstices, 

 sinking due to evaporation from a large area is more rapid than 

 the rise due to capillarity. The latter force is therefore without 

 effect for greater heights. This experiment by Nageli and 

 Schwendener was made with a cylinder of starch-paste in a long- 

 glass tube. 



The fact that the capillary attraction of the interior of the cell- 

 wall would in itself be sufficient to raise the water-column at least 

 one hundred feet is not of decisive moment, since in a unit of time 

 the sinking of the column due to evaporation is much more rapid 

 than the rising. 



2. With reference to water-movements, imbibition of the cell- 

 wall is only a special case of capillary action. In both there is 

 friction of water-molecules upon each other, there is in both a solid 

 framework within which water moves or circulates; firmness and 

 immobility of the enclosing walls are, however, not essential prop- 

 erties of a capillary system. (Compare the above with the state- 

 ments of Sachs.) 



3. The osmotic forces of the limng cells come into play. Here 

 we must make a distinction between that which osmotic forces can 

 accomplish and that which they can not accomj^lish within the liv- 

 ing woody cells, of course only in so far as our knowledge will 

 permit us to see and comprehend. Turgescent living cells no 

 doubt, under certain conditions, will force water into neighboring 

 dead elements (vessels and tracheids) in the same way as they would 

 force water into a vertical glass tube (demonstrated by experi- 

 ments). 



A high hydrostatic pressure within a living cell is joroduced as 

 follows. The water -attracting force of the substances in solution in 

 the cell -sap (nitrates, sugar, etc.) draws the water which is found 

 in the vicinity of the cell through the cell- wall and jDrimordial utri- 

 cle into the cell-lumen. The interstices in the living primordial 

 utricle are presumably very minute. As has been demonstrated, 

 the molecules of sugar in solution in the cell-sap require many 



