54 CHAP. VII. THE PHYSIOLOGICAL FACTOR 



of motile response in Mimosa, of growth, of autonomous 

 pulsations of the leaflet of Desmodium gyrans. 



D Effect due to Shock-Stimulus 



A sudden variation of external conditions causing a shock 

 gives rise to the predominant D effect. The shock may be 

 due to (a) sudden variation of pressure, to friction or to 

 mechanical disturbance of any kind ; (b) to sudden change 

 of temperature ; and (c) to sudden variation of electric con- 

 dition as produced by an induction-current or a condenser 

 discharge. The effect of shock-stimulus is seen in the 

 responsive fall of the Mimosa leaf, in the diminution of the 

 rate of growth, in the electrical response of galvanometric 

 negativity, and in the diminution of the electrical resist- 

 ance of the tissue. 



Phenomenon of Alternating Response 



After full adjustment to the external conditions, the 

 responses of Mimosa under uniform stimulus are found to 



Fig. ii. (a) Alternating Response of Mimosa (upper record), 

 and (b) of Photosynthesis (lower record) 



Note that alternating response in both tends to become uniform. 



be uniform. But during the process of adjustment to a 

 new condition, the responses are often found to be alter- 



