86 PEOPAGATION OF PLAKTS. 



attraction, and that the continuous up^rard flow is sus- 

 tained through constant evaporation and transpiration 

 ■which takes place in the buds, leaves and young parts 

 of the plant. 



Prof. J. W. Draper attributes the movement of sap to 

 capillary attraction, which he considers an electrical phe- 

 nomenon. Prof. Leibig takes a somewhat similar view of 

 the phenomenon, and thinks that as evaporation and trans- 

 piration take place in the leaves and buds, a portion of 

 the fluids are thus removed and capillary attraction is 

 promoted. Prof. Balfour is inclined to attribute the 

 movement to capillarity in the vessels of the higher plants, 

 and through the process of endosmose the continued 

 imbibition and movement of fluids is chiefly carried on. 

 These movements, he says, will of course take place with 

 greater vigor and rapidity, according to the activity of 

 the processes going on in the leaves, which thus tends 

 to keep up the circulation. Still, if a small or large root 

 of a Maple is severed twenty or thirty feet from the main 

 stem in spring, before the leaves expand, the sap will 

 flow from the wound with as much force as it will from 

 a branch or twig of the same size and the same distance 

 from the base of the stem, a fact that does not appear to 

 estabhsh the theory of capillary attraction. 



It is quite evident, however, from what we do know 

 about the movement of fluids in plants, that there are 

 different forces that act and assist in their movements, 

 and it may be due in part to vital force — variation in 

 temperature, or those changes which result from the 

 action of light and air — and partly from capillary attrac- 

 tion following the continuous loss by evaporation, which 

 must constantly affect the density of the fluids, thereby 

 promoting endosmose and exosmose action. 



In many herbaceous and acquatic plants there is a 

 rotary or spiral motion of the fluids within each individ- 

 ual cell that can be readily sees with a magnifier of mod- 



