GRAVITY AND LIGHT .10.1 



that light can get to it only from one direction. In 

 a day or so the shoot will have bent round towards 

 the light, and again as in the experiment with the 

 stem laid horizontally, it is only the young growing 

 part that bends. This curving is called heliotropism, 

 and an organ which bends towards the light is said 

 to be heliotropic. The stalks of the leaves also bend 

 till the blades face the light, at right angles to its 

 direction, and with the upper side towards it. The 

 blades of leaves may in the same way be said to 

 be dia-heliotropic. These two actions take place very 

 commonly in nature. We may see examples of it 

 in any garden, in any clump of trees, wherever in 

 fact a plant is shaded on one side. 



Most roots, on the other hand, bend away from the 

 light, as can be seen quite easily by repeating the 

 experiment with the germinated bean fixed to a cork, 

 but with black paper pasted more than half way round 

 the bottle, so that light enters only from one side. 

 Roots are therefore said to be ap-heliotropic. This 

 apheliotropism of roots is less commonly seen in 

 nature than the heliotropism or the apogeotropism of 

 stems, because, of course, roots are mostly under- 

 ground. But it can often be seen in the hanging 

 roots of the Banyan, which curve a little towards a 

 less lighted side, generally that on which is the trunk. 

 But as in the other case, so in this, there are a few 

 exceptions, to which we shall have to refer later on. 



3. Roots are affected also by moisture, towards 

 which they will always make their way, growing 

 into the dampest places in the soil. So that, if, when 

 a plant is watered, the water is only poured just near 



