50 



THE VEGETATIVE ORGANS 



shoots above ground droop or ' wilt ' , but on renewing the 

 water-supply they become turgid, i. e. the tissues absorb 

 water. The leaves expand and once more become firm. 

 Water is essential to enable a plant to maintain its firmness. 



Fig. 23. Osmosis Experiment. 

 a, thistle funnel containing sugar solution ; b, jar of water. 



Osmosis 



Osmosis is a natural process which has an important 

 bearing on the work of roots. We shall best understand 

 it by means of the following experiment. Obtain a thistle 

 funnel and with a piece of moistened parchment paper 

 close the mouth of it as in Fig. 23. Tie the paper firmly 

 round the rim and seal the junction carefully with vaseline, 

 paraffin, or plasticine. Fill the bulb of the funnel with 

 a strong sugar solution and suspend it in a jar of water. 



