408 



MOVEMENTS. 



known as the cfhin^tat. It consist?- of a clock-work which car- 

 ries a disc on which can be placed growing plants : by the revo- 

 lution of this horizontal disc all parts are in turn given the same 

 amount of illumination. If the clock-work is so arranged as to 



O 



rotate a horizontal shaft to which a growing plant can be arh'xed, 

 any one part of the plant will be exposed to the influence of 

 gravitation in precisely the same manner and to the same extent 

 as all other part-. 



When circnmnntation is plainly modified by unequal growth, 

 striking disturbances are produced which have received much 



investigation. Among these cases are the changes of position 

 which many peduncles undergo during the development of flow- 

 ers and fruits. Although the extremity of the flower-stalk passes 

 through its definite orbit, it is in some instances so affected by 

 the greater growth of the upper side as to curve downwards, 

 while a similar excessive growth on the under side will produce 

 an upward curvature. De Vries, who has given much attention 

 to these phenomena, has coined the adjectives ej)inastft\ denoting 

 curvature from growth on the upper side, and hyponastic^ that 

 from growth on the under side of an extending organ. 



FIG. 180. Disc of a clinostat covered by a glass case*/, and bearing two "Windsor 

 beans with primary and secondary roots. 



