WORK OF ROOTS IN ABSORPTION 35 



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. 



58. Turgor in the plant cell is 

 sometimes illustrated in the following 



way. A medium-sized vial is filled with 'puncturing an 



a saturated solution^! sugar. Over the jf 



open end a piece of bladder membrane m water * 



which has been thoroughly soaked is 



securely tied in such a way as to exclude F; 



the air. The vial is then immersed in Same as Fig. 



39 after needle 



a vessel of water and allow r ed to stand is removed. 



for a day or two. It is then taken from 



the vessel of water. The' membrane is arched upward as if by 



a pressure within. If the membrane is pricked with a needle, 



and the instrument quickly withdrawn, a stream of water spurts 



out because of the inside pressure. 



59. 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 prg a - ni ' r "^nrp j 

 the disintegrated remain?? of plants When soil is not saturated 

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

 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 the soil particles meets and joins with adjacent 

 soil particles at their points of contact, thus making a continuous 

 film for a great extent through the soil, reaching down to the 

 ground water below. The spaces between the soil particles are 

 filled with air, which is very necessary for the health of the plant. 

 The root hairs of plants being attached^very closely and firmly 



