5S PLANT RESPONSE 



when the pulvinus was directly stimulated, the result now 

 being the true excitatory fall alone. In the case of Arto- 

 carpus I obtained the same result. Direct stimulation was 

 here applied, at the motile region, by electric induction 

 shocks, the electrical connections being made on two sides 

 of the pulvinoid, by means of thin flexible spirals of tinsel 

 which did not offer any obstruction to the free move- 

 ment of the responding leaf. The response thus obtained 

 was normal, and unattended by any preliminary positive 

 twitch. 



The motile responsiveness of Artocarpus, then, is seen 

 to follow that of BiopJiytum or Mimosa, even in details. 

 An instance of this is found in the fact that in all three 

 cases abnormal increase of turgidity is unfavourable to the 

 manifestation of mechanical response. Thus, just after the 

 rainy season, the Artocarpus is highly turgid, and response 

 not easily obtainable. But in November, when the turgor 

 has become moderate, its motile indications are once more 

 made conspicuous. 



If the motile region be extended, or diffuse, the responsive 

 action when the stimulus is applied at any single point becomes 

 very complicated. For we have, first, the preliminary hydro- 

 static pulse, travelling along the whole length of the motile 

 organ, and producing a somewhat long-continued erectile 

 effect, which is, therefore, unlike the quickly exhausted 

 erectile twitch that took place during the short passage of 

 the hydrostatic pulse through the restricted pulvinoid. And, 

 secondly, follows, in the wake of this, a wave of negative 

 turgidity-variation concomitant to the passage of true excita- 

 tion. Such complicated effects may be avoided, however, by 

 applying electrical stimulus simultaneously throughout the 

 whole area. The electrical form of stimulation has therefore 

 certain advantages, but it is apt to bring on quick fatigue of 

 the tissue. 



Localisation of motile areas. 1 shall now deal with' some 

 further difficult points, in connection with the motile response 

 of the leaf. And first comes the question of localising 



