THE GROWTH OF THE PLANT 



99 



The shoot also continues to grow in the direction in 

 which it is placed and does not turn upwards (Fig. 49). 



Inferences. — The direction of growth of both the root 

 and the shoot is influenced by gravity. In the case of 

 the root the influence is a positive one, the root being 

 attracted towards the centre of the earth ; the influence 

 is negative in the case of the shoot. 



Geotropism is the term used to denote the way in 

 which the plant reacts in response to the stimulus 

 exerted by gravity. The main root is said to be posi- 

 tively geotropic, since it grows towards the earth's 

 centre. Shoots, on the other hand, are negatively 

 geotropic. 



Experiment 63 



Aim. — To show the curves taken by the root and 

 shoot in response to gravitational stimulus. 



Method. — A broad-bean is suspended over a gas-jar 

 of water and left to ger- 

 minate. When the main 

 root has reached almost to 

 the bottom of the jar and 

 the lateral roots are well 

 developed the mouth of 

 the jar is closed with a 

 cork. This can be done 

 by boring a hole in the 

 cork large enough to fit 

 the top of the root and 

 then cutting the cork into 

 two pieces.' The cork is 

 made secure with paraffin 

 or plasticine. The appara- 

 tus is then inverted (Fig. 

 50). 



Observations. — The 

 shoot curves and continues 

 upwards. 



Fig. 50 



its growth vertically 



