22 Plants and their Ways in South Africa 



Ex. 7. Cover the outside of the glass germinator or of a funnel with 

 several thicknesses of flannel. Fasten seeds which have just germinated 

 by means of a narrow strip of flannel to the upper edge of the glass. 

 Keep the flannel moist, and the roots will follow the inclined face of the 

 germinator instead of growing vertically. The flannel must not be too 

 moist, or the roots will turn from it. 



Ex. 8. Growth Curvatures caused by Light. — Place the germinator 

 in a box lighted at one end. Notice the seedlings in a day or so. The 

 stems will bend towards the lighted end. Will the roots show a turning 

 away from the light ? 



The seedlings of sunflower are very sensitive to light. 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 away from the light. Will they turn back ? Try the experiment 

 with other seedlings. 



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

 cluding the cotyledons, have turned toward the window. The 



Fig. 30. — The plant in this pot grew on the north side of a large rock. 

 The portion beside the pot grew on the south side in the shade. 



stalks {petioles) of the cotyledons have curved so as to bring 

 the surface of the cotyledons into a favourable light position. 



