WORK OF THE ROOT 53 



as follows (Fig. 24) : Cut a slice from one end so that each 

 potato will stand upright, and pare from this end a ring of 

 skin to the height of three-quarters of an inch. Cut a slice 

 from the other end of each potato, and bore a hole an inch 

 in diameter through the middle nearly to the lower end. 

 Fill half of this hole with sugar and add a little water to 

 moisten it. Now stand each potato upright in a dish con- 

 taining sufficient water to cover the peeled surface. Place 

 the two dishes side by side and allow them to stand for 

 two or three hours ; then compare them. In the living 

 (unboiled) potato the liquid rises 

 steadily in the cavity and eventually 

 runs over the margin. The dense f^S~^S\ 



sugar solution has withdrawn water / \ a 



from the cells lining the cavity, the I 4 \ 



sap of these cells thereby becoming I L 



concentrated. These cells now with- p^~^^^^ l b 

 draw water from those farther lc^__ _--<> 



outwards ; and this is repeated 



.. , c . , , Fig. 24. Potato 



until the cells of the pared surface osmometer.-*, cavity 



outside, which draw water from the in potato containing 



dish, are reached. Very different is sugar ; b, dish of water. 



the behaviour of the cells of the 



other potato, which have been killed by boiling. Compare 



the amount of water absorbed in the two cases and the 



difference in level of the liquid in the two cavities. In the 



living potato the liquid rises in the tube and eventually 



overflows, in the other exchange is very slow indeed. This 



will help us to realize the activity of living tissues in 



taking up and transmitting water, as compared with the 



action of a dead tissue. 



We are now in a position to understand the importance 



of root-hairs to a plant. The root-hair region, together 



with the younger part of the root which has not yet formed 



root-hairs, is the special organ for the absorption of water. 



