THE DEATH-SPASM IN PLANTS 151 



mcnt is produced. It follows that if wc could bring on very 

 gradually those conditions which cause death, then, on arrival 

 at the critical point, we might expect the irreversible mole- 

 cular derangement to occur abruptly. If, further, throughout 

 this process, the organ could be protected from stimulation, 

 we might expect that this sudden molecular derangement 

 would also be attended by a correspondingly sudden evidence 

 of excitation, which would in this case, however, be at once 

 the first indication of excitation and the last sign of life. 

 This spasmodic movement we shall designate as the death- 

 response. 



As regards the protection of the experimental organ from 

 accidental stimulation, it is to be remembered that excitation 

 under ordinary circumstances depends upon some sudden 

 variation of environmental conditions. A sudden change of 

 temperature may thus act as a stimulating agent and produce 

 depression of the leaf But a gradual change will not act as 

 a stimulus. The effect of such a gradual variation, on the 

 contrary, as will be shown presently, is to produce no excita- 

 tory contraction whatsoever. 



If now we take a specimen of Mimosa and place it 

 suddenly in warm water, say at 35^" C, a responsive collapse 

 of the leaves will at once occur. But if the plant be placed 

 in water at the ordinary temperature of the room, and the tem- 

 perature gradually raised — say at a rate of 1° per one minute 

 and a half, or thereabouts — there will be no responsive 

 downward movement whatsoever. On the contrary, owing 

 to absorption of water by the organ, and also to the re- 

 laxing physiological action of heat, a delicate method of 

 record will show a slight and continuous movement upwards. 

 This proceeds till we reach a degree of temperature which 

 proves to be the death-point. For example, in the case of a 

 particular experiment in summer, with a young leaf of 

 Mimosa, when the temperature of 59° C. was reached, there 

 was a sudden spasmodic movement of the leaf downwards. 

 This was, in fact, the death-throe of the plant. In winter, 

 after a spell of cold weather, when the physiological condition 



