34 



Gardening 



2. To show that a leaf gives off water. Draw the stem of a 

 healthy young leaf (cabbage or geranium Will do) through a hole 

 in a square of cardboard. Seal about the stem of the leaf with 



FlGS. 25, 26, and 27. Experiments to show that leaves give off water. 



paraffin heated only to the melting point (too hot paraffin will 

 kill the stem of the leaf and spoil the experiment). Then arrange 

 the experiment as in Figure 25, making sure that the upper drink- 

 ing glass fits snugly to the cardboard. 



Arrange two other glasses in the same manner but make no 

 hole in the cardboard and omit the leaf. Set both pairs of glasses 

 in the sunlight for several hours. 



Where does the water come from that collects in the glass 

 inclosing the leaf? What happens to a leaf if it is not supplied 

 with water? 



The second pair of glasses is used as a "check" or "control" 

 in the experiment. Why is it advisable to have a check in experi- 

 mental work ? 



That a plant gives off water can be shown also in the manner 

 indicated in Figures 26 and 27. When the experiment is carried 

 out as suggested in Figure 26, the twig is left attached to the tree. 

 When done as indicated in Figure 27, the leaves should be placed 

 in the sun. 



Transpiration may be demonstrated also by turning a large glass 

 vessel over a potted plant, after the pot has been wrapped in sheet 



