GROWTH AND TROPIC 

 MOVEMENTS OF PLANTS 



CHAPTER I 



introductory 



Growth and Tropic Movements of Plants 



In my ' Motor Mechanism of Plants/ published a year ago, 

 detailed accounts were given of investigations on the motor 

 mechanism of adult members, such as the leaves of sensitive 

 and other plants. A very large and extensive class of 

 phenomena still remained to be dealt with, namely, the 

 movements of growing organs induced under external 

 stimulation. The consideration of these responsive move- 

 ments of growing organs forms the main subject of the 

 present volume. 



The movements induced in a growing organ by external 

 stimulation are extremely diverse. The effective agents 

 are manifold — the stimulus of contact, of electric current, 

 of gravity, of radiation visible and invisible, and the rise 

 and fall of temperature. They may act on organs which 

 exhibit all degrees of physiological differentiation, from 

 the radial to the dorsiventral. An identical stimulus some- 

 times induces one effect, and at other times precisely the 

 opposite. Thus, under unilateral stimulation by light of 

 increasing intensity, a radial organ exhibits first a positive, 

 then a dia-phototropic, and finally a negative movement ; 



