22 Plants and their Ways in Sottth Africa 



Place some in a , bright light and cover with black paper, 

 leaving an opening at one side. Notice how the cotyledons 

 turn their flat surfaces to the light. As soon as the next pair 

 of leaves appear, reverse the position, so that they turn directly 



Fk;. 29. — Leaves of young Castor-oil plant looking toward the light. 



away from the light. Will they turn back ? Try the experi- 

 ment with other seedlings. 



Fig. 29 shows a young castor-oil plant. All the leaves, 

 including the cotyledons, have turned toward the window. 

 The stalks {petioles) of the cotyledons have curved sa as to 

 bring the surface of the cotyledons into a favourable light 

 position. The cotyledons of the bean have no petioles. On 



