14 EXPERIMENTAL PLANT PHYSIOLOGY 



L^^ 



EXPEEIMENT 6 



Aim. — To determine what takes place when a sugar 

 solution and water are separated by a permeable mem- 

 brane, such as pig's bladder or a piece of parchment. 



Method. — A piece of pig's bladder or parchment is 

 soaked in water, then tighuy stretched over the mouth 

 of a long-stemmed thistle-funnel and tied on with thin 

 string. The stem of the thistle-funnel is then held 

 obliquely while golden syrup or a strong sugar solution 

 is poured into the funnel until the 

 bulb is full. If syrup is used it 

 must be warmed so that it can 

 flow down the tube easily, but it 

 must not be made hot enough to 

 ;^^ — . injure the bladder. Syrup is easier 

 to use than a sugar solution, as 

 the latter may crystallize ovit if it 

 is too strong. 



When the bulb is full the thistle- 

 funnel is fixed in an erect position 

 by means of a clamp and retort- 

 stand, and the level of the syrup is 

 marked with a strip of gummed 

 paper. The bulb is then suspended 

 in a beaker of water in such a way 

 that the level of the water in the 

 beaker is the same as that of 

 the solution in the thistle-funnel 

 (Fig. 4). 



Observations. — The liquid in the 

 tube begins to rise and continues so to rise for some 

 considerable time. Finally a maximum height is 

 reached; and then the level of the liquid in the tube 



fets gradually lower. Meanwhile the water in the 

 asin gets sweet. 



Inferences. — The sugar must, in some way, have 

 attracted the water through the bladder, and this with 

 so much force that the liquid was able to rise in the 

 tube against the force of gravity. 



Fig. 4 



