WORK OF ROOTS IN ABSORPTION 41 



in the tube are at the same level. In a few hours or in a day or so, 

 if the experiment is properly set up, the solution in the tube will 

 rise above the surface of the water in the bottle. Water then 

 flows through the membrane into the sugar solution, but the 

 sugar and the dye do not pass through the membrane to any great 

 extent unless left for a long time. 



65. Turgor in the plant cell is sometimes illustrated in the 

 following way: A medium-sized vial is rilled with a saturated 

 solution of sugar. Over the open end 



a piece of bladder membrane which 

 has been thoroughly soaked is securely 

 tied in such a way as to exclude the 

 air. The vial is then immersed in a 

 vessel of water and allowed to stand 

 for a day or two. It is then taken 

 from the vessel of water. The mem- 

 brane is arched upward as if by a 

 pressure within. If the membrane is 

 pricked with a needle, and the instru- 

 ment quickly withdrawn, a stream of water spurts out because 

 of the inside pressure. 



66. How the root hairs get water from the soil. Most 

 land plants get their water and food solutions from soil which is 

 moist or sometimes even appears dry. How can they take up 

 water from moist soil or from soil which is so dry that no water 

 can be pumped from it? The soil is composed of very finely 

 pulverized rock, in the form of minute angular grains. Mixed 

 with these fine grains is more or less matter of an organic nature, 

 the disintegrated remains of plants. When soil is not saturated 

 with water, the water present is in the form of a thin film which 

 surrounds the soil particles. The soil particles touch each other, 

 but because of their form there are spaces between them just as 

 there are spaces between the stones in a pile. The film of 

 water which surrounds a soil particle meets and joins with the 

 film surrounding adjacent soil particles at their points of contact, 

 thus making a continuous film for a great extent through the soil, 



