24 Plants and their Ways in Soiitli Africa 



matter of common observation that a potato, e.g. wliich has 

 grown in a dark place, will have a very long stem. It used to 

 be thought that light hindered growth, but dark places are 

 usually damp. It has been found in experiments on bamboos 

 and other plants that light had no effect on their growth, which 

 varied with the humidity of the air and the temperature. 

 Growth is favoured at night when transpiration ' decreases and 

 the cells are consequently distended with water. The food 

 su[)ply also has an effect on growth. 



' Sue p. 30. 



