REVIEW OF RESPONSE OF ISOTROPIC ORGANS 695 



(fig. 206), the animal stomach (fig. 213), nerves of animals, 

 and the retina (fig. 252). 



I have also shown that there is no strict line of 

 demarcation between the phenomena of such multiple 

 response and autonomous response so-called. Biophytum, for 

 example, which, usually speaking, exhibits a single response 

 to a single moderate stimulus, and multiple response to a 

 strong stimulus, will, under exceptionally favourable tonic 

 conditions that is to say, when it has absorbed from its 

 surroundings an excess of energy exhibit responses which 

 are apparently autonomous. A typically autonomous plant 

 like Desmodium gyrans, again, when deprived by unfavour- 

 able circumstances of that excess of energy which it 

 requires, will be reduced to the condition of a multiply 

 responding plant merely. It then responds by a single 

 response to moderate, and by multiple responses to strong, 

 stimulus. When the energy imparted by strong stimulus is 

 exhausted, these multiple responses come to a stop, to be 

 once more renewed, on a fresh accession of strong stimulus. 

 Or a lateral leaflet of Desmodium^ originally quiescent, may 

 be put into, and maintained in, a state of pulsation by the 

 action of sunlight. 



It is from the stored-up energy derived from its 

 surroundings that the tonic condition of the plant is so 

 raised as to maintain its so-called autonomous activity. 

 From this it will be seen that, strictly speaking, there is no 

 such thing as automatism. Movement can only be produced 

 by the immediate action of stimulus, or by energy previously 

 absorbed. 



In recording the autonomous pulsation of the lateral 

 leaflets of Desmodium gyrans, it is found that while the 

 down-movement brought about by the contractile action of 

 the lower half of the pulvinule is very rapid, the up-move- 

 ment due to recovery, and to contraction of the upper half 

 of the organ, is relatively slow. The two alternating 

 excitatory impulses, in the lower and upper halves respec- 

 tively, are in the ratio approximately of 1-5 to i. This 



