THE LEAVES 67 



10. Experiment to shew that leaves give oflF 

 water. Take a number of freshly cut leaves : place 

 them on a level surface, and cover them with a glass 

 jar or a bell-glass. In a short time you will see the 

 water vapour beginning to make the inner surface of 

 the glass dim ; and after a few hours water drops 

 will form. Since you cannot see the water passing off 

 from the leaves, it is clear that the water is given off 

 by the leaf in the form of water vapour. But you may 

 say that these leaves were cut, and that the water may 

 have come from the cut stalks. Well, let us try the 

 same experiment with an uncut plant. Take a small 

 pot-plant and cover the pot and the earth tightly with 

 some oil-cloth or oiled paper or sheet rubber. Tie 

 this covering so that no moisture can escape from the 

 pot or the earth. Then cover the plant with a bell- jar. 

 The glass will become dim, and the water drops will 

 form as before. 



Note. — Experiment to prove the presence of starch in any strongly grow- 

 ing leaves : If the leaves be placed for a few minutes in boiling water, and 

 then for a short time in warm alcohol, the green colouring matter will 

 disappear. Then place the leaves for a few hours in a dilute alcoholic 

 solution of iodine. Then rinse in water, and place in a saucer full of water.. 

 The dark or dark bluish colour will shew the presence of starch. 



Questions and Exercises. — 



(1) If you leave a board on grass for a few days, what effect has. 

 it on the colour ? Explain. 



(2) The variegated Danubian reed — " bamboo " — (%.e. the variety 

 with white bands running up the leaves) does not grow so 

 vigorously as the ordinary green variety. How is this ? 



(3) Leaves cut for fodder in the evening are richer in starch than 

 leaves cut in the morning. How ? 



(4) When you store up force in a clock by winding it up, you 

 know that you will get back the same amount of force in the 

 clock's movement. How does a grain of starch resemble a clock 

 that has been wound up t 



(5) Tell any of the kinds of work by which a plant uses the sun- 

 force that it has stored up. 



