80 LUTHER BURBANK 



matter for debate, and that there is not entire 

 unanimity among plant physiologists as to the 

 forces that are involved. That osmosis has a 

 share, no one doubts. But it is alleged that the 

 principle of capillarity through which liquids are 

 drawn into minute tubes also has a share in ele- 

 vating the water in the plant. 



And it is further suggested that the constant 

 transpiration of water from the leaves of the 

 plants acts as a sort of suction force drawing the 

 water upward. It should be understood, how- 

 ever, that this alleged suction power, when an- 

 alyzed, is nothing more than a drying out of the 

 cells of the leaf which makes them more absorbent 

 and thus brings into play the principles of osmosis 

 and capillarity through which they take up a new 

 supply of water from neighboring cells. 



Thus, properly understood, the effect of trans- 

 fusion of water to the leaves is to be interpreted 

 in terms of osmosis, and capillarity. 



So also must be interpreted the so-called root 

 pressure through which water is forced upward 

 into the stem of the plant at a time when the plant 

 has no leaves — as in case of a tree in the early 

 springtime. Such root pressure undoubtedly 

 exists, but this also is explicable as due to the 

 absorption of salts in solution by the rootlets from 

 the water in the soil about them, leading to 



