CHAPTER VI. 



THE FUNCTIONS OF ROOT-HAIRS. 



Excretions from root-hairs Osmotic phenomena Tur- 

 gescence Plasmolysis Control of the protoplasm in 

 absorption, etc. Selective absorption. 



We see then that the root-hairs are the active 

 living instruments in absorbing the water (con- 

 taining small quantities of dissolved substances) 

 of the soil. 



If the living root-hairs are so numerous and so 

 active, however, a natural inference is that they 

 must exert some influence on the composition 

 or arrangement of their environment. All the 

 teachings of modern physiology go to show that 

 such a living cell as I have sketched cannot carry 

 on its life, brief though it be the root-hairs are 

 active for about four or five days without forming 

 substances of the nature of excreta, and we should 

 expect some of these to pass out to the soil. 



Sachs showed, in i860, that roots growing in 

 contact with polished marble corrode the surface 



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