CHAPTER XXIV 



AN INQUIRY INTO THE CAUSES OF AUTONOMOUS 

 MOVEMENTS 



Production of pulsatory movements as after-effect of energy absorbed — Physical 

 analogue — Localisation of seat of automatic excitation in Desmodium — 

 Demonstration of multiple response to a constant stimulus: (i) Chemical — 

 (2) Electrical — (3) Stimulus of light — Multiple response to constant stimulus 

 of light, in : (a) retina— (b) Biophytum — (c) Desmodium — (4) Thermal — 

 Induction of automatism in Biophytum at favourable temperature — (5) Of 

 internal hydrostatic pressure — Absorption of external energy and its absorption 

 by the plant in latent form — True meaning of ' tonic ' condition — Cause of 

 rhythmicity — After-effect, and its relative persistence. 



In living tissues, both animal and vegetable, we find 

 numerous cases of spontaneous periodic movements, to 

 which no direct exciting cause is apparently assignable. 

 We confess our inability to trace out the exciting cause 

 by classing such phenomena as automatic. Among well- 

 known examples of automatic movements in animal tissues 

 may be cited the pulsatory action of the heart. In the 

 vegetable kingdom, also, such movements are very numerous, 

 and are of various degrees of rapidity, from quick pulsations 

 of some few seconds in duration, to others which occupy 

 periods of several hours. It is to be remembered that these 

 spontaneous movements take place in plants under favourable 

 circumstances, i.e. under that totality of the optimum degrees 

 of light, temperature, turgidity, and so on, which is vaguely 

 referred to in vegetable physiology as the tonic condition. I 

 intend to set forth presently experimental considerations 

 which will, I hope, serve to make clear the precise significance 

 of this term. 



As already said, to call such movements automatic is 



