CHEMICAL REAGENTS ON AUTONOMOUS PULSATION 327 



be found important, as touching a later investigation on 

 the ascent of sap. It is to be noticed that the petiole 

 allows the poisonous solution which kills it to pass upwards 

 through it. 



Spark-record of pulsation of Desmodium.— Before 

 ending this chapter, I shall give a spark-record of a single 

 pulsation in a leaflet of Desmodium. The successive sparks 

 were produced at intervals of 

 5 seconds, and a glance at 

 the record affords a visual 

 demonstration of the peculiar 

 characteristics of the move- 

 ment of the leaflet. The 

 up line as usual indicates 

 down movement. It is thus 

 seen that, after a pause in 

 the highest position, a sudden 

 excitatory impulse is de- 

 veloped, which is gradually 

 exhausted, as the lowest 

 position is reached. The up movement takes place more 

 gradually, and at a much slower rate. The results are shown 



Fig. 134. Spark-record of Single Pul- 

 sation in Leaflet of Desmodium 



Interval between successive sparks 

 = 5 seconds. 





Summary 



The effect of a chemical reagent on a plant is modified to 

 some extent by the tonic condition of the tissue. A vigorous 

 plant will, generally speaking, withstand for a considerable 

 time the action of deleterious agents ; a weakly specimen 

 succumbs more quickly. 



