ABSORPTION AND MOVEMENT OF WATER 121 



and through the cavities of ducts and tracheids is demon- 

 strated by using a solution of gelatine, which melts at a 

 temperature so low as not to injure the plant, but which is 

 solid at ordinary temperatures. For example, gelatine 

 melted at about 30 C. will be taken into the freshly-cut 

 butt of an amputated branch and can then be hardened by 

 plunging into water at 20 C. If now the branch, with the 

 butt freed from superfluous adherent gelatine, is stood up in 

 a jar of cool water its leaves w r ill wither. They will recover, 

 however, if placed in water warm enough to melt out the 

 gelatine. This experiment is significant in two ways at 

 least. First, solid gelatine permeated with water is no bar 

 to osmotic transfer of aqueous solutions, while paraffine, or 

 any similar material which is impermeable to water but 

 might also be used to fill the cavities of the vessels, would 

 stop osmosis. We see then that osmotic transfer, even if it 

 could take place in the ducts as it does between the paren- 

 chyma cells, is too slow for the conduction of more than 

 small volumes of solutions and for short distances. Second, 

 if the solidified gelatine is properly removed from the sur- 

 face of the butt of the branch experimented upon, little or 

 no penetration of gelatine into the walls of the ducts having 

 taken place^ the permeability and conducting-power of the 

 walls will be only very slightly diminished if impaired at all. 



Further than this no positive assertions can be made. 

 The water certainly ascends, mainly in the cavities of ducts 

 and tracheids, though also in the walls, and whenever the 

 physical conditions demand it, water and dissolved salts will 

 be drawn from the phloem as well as from the xylem. The 

 main path for the transfer of the solutions of food-materials 

 is the wood ; for the transfer of the solutions of elaborated 

 foods, the phloem or bast-portion of the vascular bundles. 

 The physical force needed to raise the water is still unknown. 



Of the various views regarding the means of transfer to 

 which reference was made on pages 119 and 120, one is further 

 from disproof, perhaps also from proof, than the others. This 

 is the one put forth by Godlewski, * and advocated in more 



* See Pfeffer, Pflanzenphysiologie, Bd. I., p. 208 ; Engl. transl., I., pp. 

 220 et seq. 



