548 LIFE MOVEMENTS IN PLANTS 



the movements which are autonomous from others which 

 are paratonic, i.e., brought about by external stimulus , to 

 the former class belongs a large number of automatic 

 activities ranging from the quick pulsations of Desmodium 

 gyrans to the slow movements, exhibited by epinastic and 

 hyponastic organs. Under the category of nastic move- 

 ments may also be included those of the flower of Crocus 

 and Tulijj, in which variation of temperature induces 

 differential growth on two sides of the organ. The direc- 

 tion of the movement, though initiated by change of tem- 

 perature, is determined by the difference of growth-activity 

 on the two sides. In these instances of nastic movement, 

 the induced curvature is in relation of the plant; the 

 opening of the flower due to rise of temperature will remain 

 the same, whether the flower be kept in an erect or in 

 an inverted position. Had the movement, on the other 

 hand, been paratonic, that is to say, due to the external 

 stimulus of gravity, the responsive movement would have 

 been determined not in relation to the plant but to the 

 direction of external force of gravity. 



In the description of direction of responsive move- 

 ments, confusion is likely to arise unless the point of view 

 be carefully defined. An up-movement of a leaf or a 

 petal means approach towards the growing point of the 

 axis. This may be variously described as movement of 

 closure or of folding. A down-movement may, on the 

 other hand, be described as a movement of opening or of 

 unfolding. If the plant be held inverted, two different 

 effects will be noticed depending on the character of the 

 movement, whether nastic or tropic. In the case of nastic 

 movement, the former up-movement in erect position would 

 appear, on inversion of the plant, to be a down-movement ; 

 but in relation to the plant the closure movement will 

 remain closure movement, whether the plant be held in 

 the normal position or upside down. If, on the other 



