100 EXPERIMENTAL PLANT PHYSIOLOGY 



The primary root bends over and grows vertically 

 downwards. 



The lateral roots turn obliquely downwards. 



Experiment 64 



Aim. — To find out what part of the root is sensitive 

 to gravity. 



Method. — Two broad-bean seedlings with radicles of 

 about one to two inches long are fixed to a strip of 



Fig. 51 



Fig. 52 



sheet cork and suspended in a damp atmosphere with 

 their radicles in a horizontal position. 



The strip of cork may be suspended by means of 

 cotton in an inverted bell-jar standing in a dish of 

 water. A greased glass-plate can be put over the base 

 of the iar so that the air within may be kept damp 



(Fig. 51). y f v 



The seedlings are drawn carefully before being 

 attached to the cork (Fig. 51, a and b). 



They are again drawn after twenty-four hours (a' 

 and b'). 



