THE GROWTH OF THE PLANT 



105 



long is selected. The tip. of the root for a distance of 

 fifteen millimetres is then divided off into millimetre 

 lengths by means of Indian ink as described in Ex- 

 periment 67. 



A strip of sheet cork is cut having a length equal to 

 the diameter of a crystallizing dish or other glass 

 vessel. The seedling is pinned to the strip of cork. 

 Water is put into the glass vessel and the strip of cork 

 then fixed above the water so that the root of the seed- 

 ling lies horizontally (Fig. 55). 



Observations.^Within twenty-four hours the tip of 

 the root is found to have turned vertically downwards. 



-y-^ 



Fig. 55 



The part at which the curve has taken place is the 

 region of the greatest growth. That part of the root 

 which has ceased growing remains horizontal. 



Inferences. — Gravitational stimulus is operative only 

 on the growing portion of the root ; and when placed 

 in a horizontal position the radicle curves downwards, 

 the point of curvature being the region of greatest 

 growth. 



Experiment 69 



Aim. — To find out in what part of the shoot growth 

 takes place. 

 Method. — Any rapidly growing plant can be used for 



