THE FOOD OF PLANTS 



CHAP. 



to pass through. 



Cut the cork in half through the 

 middle of this hole. Fit 

 the cork closely round the 

 branch. Nearly fill the 

 bottle with water, and 

 insert the cork with the 

 branch. Place the bottle 

 on a balance, weigh it, 

 and note the weight. 

 Then take the bottle off 

 the balance and place it 

 out in the sun as before. 

 In a short time the. water 

 will begin to sink in the 

 bottle, showing that the 

 broken end of the stem 

 is able to draw up the 

 water. After it has been 

 for a few hours in the 

 sun weigh again. It now 

 weighs much less, show- 

 ing that the water has 

 escaped into the air. 



If we now pick off the 

 leaves, the water will practically cease sinking in 

 the bottle, and the bottle will no longer lose weight 

 appreciably. 



Evidently then the water is escaping from the 

 surface of the leaves, and as it is not dripping from 

 them, it must be passing off in the form of vapour. 



