ABSORPTION AND OSMOSIS 67 



1. Large extent of surface. 



2. Thin walls for osmosis. 



3. Location for protection and large contact with soil. 



4. Acid secretion to dissolve mineral matter. 



Geotropism. (Contrast action of mere weight.) 

 Definition. 

 An adaptation for 

 Penetration of soil. 

 Obtaining water in soil. 

 Obtaining nourishment. 

 Positive in roots. 

 Negative in stems. 

 Hydrotropism. 

 Definition. 



Function, reaching water supply. 

 Selective absorption. 



Meaning of term. How controlled. 

 Successive osmosis. 



Meaning of term. Explanation. 

 Root pressure. 



Meaning of term. Reverse osmosis. 

 Experiments with roots: Geotropism; Hydrotropism. 



