THE PROPERTIES OF SOIL 37 



open at both ends, and place a piece of 

 bladder across one end, subsequently filling 

 it with a strong solution of sugar, and then 

 close|the other end with a similar membrane, 

 we shall find that if the cylinder be placed in 

 a basin of water the membranes will be 

 pushed outwards owing to internal pressure 

 set up in consequence of the movement of 

 water into the cylinder. Or, conversely, 

 we may have the solution of sugar in the 

 basin, and water in the cylinder, when the 

 membrane will be pushed inwards owing to 

 water having passed the membrane and 

 intermixed with the sugary solution in the 

 basin. Cells which are subjected to in- 

 ternal pressure, and whose membrane is 

 stretched, are said to be " turgid " ; whereas 

 cells with no internal pressure are said to be 

 in a condition of plasmolysis. The growing 

 shoot of a herbaceous plant, for instance, 

 has its cells in the turgid condition and, 

 consequently, stands erect ; but if such a 

 shoot be severed from the plant it speedily 

 becomes limp and droops, because when water 

 can no longer move up the stem to maintain 

 internal pressure in the cells the latter rapidly 

 pass into the condition of plasmolysis. 



While the requirements of plants as regards 

 water are, to the greatest extent, met by 



