CHAPTER XXXVIII 



INQUIRY INTO THE LAWS OF RESPONSIVE GROWTH- 

 CURVATURES 



Scope of the investigation : I. Mechanical response to unilateral stimulation of the 

 tips of shoot and root : (a) Moderate stimulus — (b) Stronger stimulation— 

 2. Effect of unilateral stimulus, applied at the responding growing region : 

 (a) Moderate stimulus — (b) Strong or long-continued stimulus — Experiments 

 on the direct and indirect effects of stimulus on Mimosa : (a) Direct stimula- 

 tion — (b) Indirect stimulation, longitudinal transmission — (c) Indirect stimula- 

 tion, transverse transmission — The curious response of an Aroid — Table showing 

 responsive effects common to pulvini, pulvinoids, and growing organs — Laws 

 of responsive growth-curvature. 



We were able, at the end of the last chapter, to pass in 

 review the theoretical conclusions to which we had been led 

 by the electrical mode of investigation, as to the responsive 

 movements which might be expected to follow on the 

 unilateral application of stimulus to the tip and the growing 

 region respectively. I shall now proceed to submit these 

 theoretical conclusions to experimental verification, by taking 

 records of the mechanical movements actually induced. 



It will be understood here that my object is (i) to show 

 that the peculiar response given by the tip of the root is 

 characteristic of the tip of the shoot also ; and (2) to demon- 

 strate the effect of unilateral stimulation on the growing 

 region. We have therefore to study the effects which are 

 induced at the growing region by the action of stimuli of 

 different intensities, according as they are applied unilaterally 

 at the distant tip, or, locally, on the growing region itself. As 

 a specimen of the shoot-tip, we may employ either the tip of 

 a stem or that of an unopened flower-bud. This latter, 

 composed mainly as it is of indifferently conducting elements, 



