Grozvth of Roots, Steins, and Leaves 



21 



been studying growth curvatures affected by gravity. While 

 the tendency of the main root is downward and that of the 

 stem is upward, both are sensitive to other influences. Food 

 material which roots absorb must be dissolved in water, in 

 search of which they often go a long distance. The roots 

 of a tree growing by a stream will reach far out on the side 

 toward the water. Young plants show this curvature. Cover 

 the outside of the glass germinator with several thicknesses 

 of flannel. Fasten seeds which have just germinated by 

 means of a narrow strip of flannel lo the upper edge of the 

 glass. Keep the flannel moist, and the roots will follow on 



Fig. 28. — Stem curvature induced by gravity. 



the inclined face of the germinator instead of growing verti- 

 cally. The flannel must not be too moist, or the roots will 

 turn from it. Another good way to show this curvature is 

 by fastening a pointed bag of butter-cloth to the germinator ; 

 fill it with moss or cotton-wool, and fasten the seeds around 

 the upper part of the bag. Suspend the bag in a jar. It 

 should be well drained, and no water should stand in the jar. 



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 toward the lighted end. 

 Will the roots show a turning away from the light ? 



The seedlings of sunflower are very sensitive to light. 



