LEAVES 155 



Select a vigorous potted plant of sunflower or tropaeolum 

 and lay the flowerpot on its side. On a sheet of paper make 

 a diagram of the flowerpot and one or two fresh young leaves. 

 Let the flowerpot remain so for a day, then make a sketch 

 in dotted lines on the diagram, showing the new position of 

 the leaves. 



Suggestion. Observe a geranium which has been grow- 

 ing in a window box for some time. How do the plants on 

 the sunny side compare with those on the shady side as 

 to the position and number of their leaves? 



Note. Good examples of both negative heliotropism and nega- 

 tive geotropism are seen in such vines as climb by adventitious 

 aerial roots. In the trumpet creeper (tecoma) the climbing roots 

 project away from the sun and away from the soil. Prove this 

 by the following experiment: 



Choose a stem on which the roots are beginning to attach them- 

 selves. Turn the stem half round so as to get the roots into the 

 light. Fasten the vine to prevent its return to the former position. 



After one week, observe it. Have the roots responded to the 

 change of position? 



136. LEAVES 



Object. To show that plants give off water. 

 Apparatus. As shown in Figures 67 and 68. 



Method. Cover a plant as in Figure 67, using rubber 

 tissue or waxed paper to cover the soil and a wide-mouth 

 bottle inverted over the plant. Or use a tumbler over a 

 leaf as shown in Figure 68, letting the petiole project through 

 a hole in the card which covers the battery jar, and plug 

 the hole around the stem with cotton batting. 



When the plant has been arranged according to one of 

 these ways, stand it in a shady place or one where the sun- 



