RESPONSE OF ANISOTROPIC ORGANS 



Table LV. — Effects of Exposure of the Different 



Sides to Light 



411 



The above results, which fully confirm the previous 

 conclusions, were totally unexpected, and appear at first 

 sight to be quite inexplicable. 



Torsional Response of Anisotropic Organs 



The difficulty is completely overcome on reference to 

 the Laws of Torsional Response of Anisotropic Organs 

 which have already been established (p. 256), that — 



1. An anisotropic organ, when laterally excited by any 



stimulus, undergoes a torsion by which the less excitable 

 side is made to face the stimulus. 



My present results extend this generalisation 

 to differentially growing organs also, and the wider 

 inclusive law is enunciated as follows : 



2. A differentially growing organ, when laterally stimulated, 



undergoes a torsion by which the less excitable side is 

 made to face the stimulus. The induced torsional 

 movement is algebraically summated with that of the 

 existing autonomous torsion. 



The parallel results in differentially excitable pulvinated 

 and in differentially growing organs will be clearly under- 

 stood from the following illustrative examples. 



Torsional Response of the Pulvinated Organ 



The diagram (fig. 224) will explain the principal effects. 

 The shaded lower half of the pulvinus is the more excitable, 

 and the plane of junction of the two halves is marked 



