ABSORPTION AND TRANSMISSION OF WATER 113 



poisons used by Strasburger, though, of course, in not so 

 marked a manner. They probably cause partial plasmolysis 

 in the leaf cells and thus disturb diffusion and evaporation. 

 Still another point which may be construed in this same 

 manner is the observation of Kossaroff l that an increase in 

 the amount of CO 2 in the water in which are placed cut twigs, 

 with and without leaves, is accompanied by a marked falling 

 off in water absorption. What can be the reason for this we are 

 unable even to conjecture, but it certainly appears as though 

 the chemical nature of the membranes were involved. It 

 cannot be due to the osmotic pressure of the dissolved CO 2 , 

 since this gas penetrates all protoplasts with the utmost ease. 

 Possibly the CO 2 may precipitate in the wood and form 

 bubbles which plug the water channels ; but this, too, seems 

 unlikely. It seems more probable that the dissolved gas 

 affects the protoplasmic membranes in the leaves, causing 

 some change in their osmotic properties. 



The whole problem of water ascent remains a puzzling one, 

 one which must wait for solution until the development of 

 better and more exact methods of experimentation. In the 

 meantime it will probably be more profitable to devote atten- 

 tion to some of the more definite and restricted problems of 

 the cell itself. In the present condition of our knowledge of 

 plasmic membranes, for example, it is almost foolhardy to 

 attempt to settle such a complex question as the one just briefly 

 reviewed ; but once knowing the nature of these plasmic mem- 

 branes, it is not improbable that the solution of the problem 

 of water transport will follow as the simplest corollary. 



III. SUMMARY OF THE CHAPTER 



In general, the process of water absorption and water 

 movement may be stated as follows : The imbibed water of 

 the cell walls, the water of the protoplasm itself, and the 



IP. KOSSAEOFF, "DieWirkung der Kohlensaure auf den Wassertransport in den 

 Pflanzen," Bot. CentralbL, Vol. LXXXIII (1900), pp. 138-44. 



