158 PLANT RESPONSE 



preliminary rise of the Mimosa leaf or curling of the P ass i flora 

 tendril. But at the death-point this movement was at first 

 arrested, and then reversed with accelerated speed. The 

 condition of this particular specimen was afterwards tested 

 by the electrical method, when it was found that, while a 

 portion of the peduncle previously cut off gave the normal 

 response of living tissue, the specimen which had been 

 subjected to the death-temperature gave no response. 



Summary 



The death-point of a plant, under heat-rigor, is concomi- 

 tant to the disappearance of the true excitatory response of 

 galvanometric negativity. After this point is passed, hydro- 

 static disturbance generally gives rise to the reverse positive 

 response. 



When an anisotropic organ like the pulvinus of Mimosa is 

 gradually raised in temperature, then, at a certain critical 

 temperature, a spasmodic movement is produced which 

 proves to be the death-response of the organ. This is a true 

 excitatory response. The critical death-points of similar 

 specimens are very definite and practically identical. 



The death-point is modified by the physiological condition 

 of the tissue. Other things being equal, death occurs earlier 

 with a young than with a mature tissue. 



The death-response of an anisotropic organ is composite. 

 In Mimosa it consists of a down, followed by an up, move- 

 ment. This is due to the death-contraction being followed 

 later by fat post-mortem relaxation of the organ. 



In the spiral tendril of Pass/flora, the death-response is 

 given at the critical point by a sudden uncurling. 



In the case of the hollow peduncle of Allium, the death- 

 response is exhibited by volumetric contraction, producing 

 sudden expulsion of contained water. 



