THE WORK OF ROOTS 



123 



Place it under water, and blow gently into the tube to 

 make sure there are no leaks. Pour into the tube enough 

 strong syrup (sugar and water) to fill it to 

 a point a little above the membrane. Sub- 

 merge the membrane in water, and mark 

 the height at which the syrup stands. If, 

 now, this artificial root -hair absorbs water, 

 we can detect it by the rise of fluid in the 

 tube. How rapidly does it rise? How far 

 will it rise? As we have already learned 

 (pages 61 to 63), the absorption of water 

 generates pressure inside the (closed) arti- 

 ficial root -hair. In the real root-hair 

 pressure is generated in the same 

 way. 



What happens if we now extract 

 water from the artificial root-hair by 

 submerging it in a stronger syrup 

 than that which is inside of it ? Pour 

 sugar into the tumbler and stir it un- 

 til a very strong syrup is formed; 

 what happens to the liquid in the 

 tube! Try the same experiment with the root-hairs; 

 have some seedlings with good root -hairs growing in 

 water; add sugar to the water until a strong syrup 

 is formed. The stiffness of the root-hairs is due ap- 

 parently (like the stiffness of an inflated balloon or 

 bicycle tire) to the pressure inside; this pressure is 



91. Artificial root -hair, 

 made of the mem- 

 brane which lines an 

 egg-shell. 



