LUTHER BURBANK 



nimity 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 elevating 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, however, 

 that this alleged suction power, when analyzed, 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 cap- 

 illarity through which they take up a new supply 

 of water from neighboring cells. 



Thus, properly understood, the effect of trans- 

 fusion of water from 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 

 spring time. Such root pressure undoubtedly ex- 

 ists, but this also is explicable as due to the ab- 

 sorption of salts in solution by the rootlets from 

 the water in the soil about them, leading to osmotic 

 action between these superficial cells and the ad- 



[18] 



