322 PLANT RESPONSE 



given plant, before and after the application of the solution, 

 it is necessary that the continuity of the record should be in 

 no way disturbed. For this purpose I insert the specimen 

 in the arrangement shown in the diagram (fig. 129). One 

 end of the tube is connected with a funnel, F, by means of an 

 india-rubber tubing ; the other end is provided with a .stop- 

 cock. The tube is first filled with water, and the stop-cock, 

 S, closed. The normal responses of the leaflet are now taken, 

 with the petiole in water. Next, by proper manipulation of the 

 stop-cock, the water is allowed to run out, and its place is taken 

 by the chemical solution which is passed in at the funnel. The 

 record which is now taken exhibits the effect of the drug. 



The second of our three methods of experiment is that of 

 direct application — that is to say, touching the motile organ 

 itself with a drop of the solution. In this case, the modifi- 

 cation of response takes place rapidly. And, lastly, gaseous 

 substances may be introduced or withdrawn from the plant 

 chamber, by means of suitable inlet and outlet pipes. 



Action of chemical reagents modified by ; tonic con- 

 dition of tissue ; strength of solution ; duration of appli- 

 cation. — There are certain general considerations of a very 

 significant kind which it will be well to specify at this point. 

 Though the fundamental effect of any given reagent is 

 definite, yet certain minor variations of this effect, due to 

 the constitution of the individual plant, are liable to occur, 

 and these are often extremely suggestive. Two successive 

 experiments, for example, were performed to determine the 

 action of the poison mercuric chloride on different specimens ; 

 one of these was extremely vigorous, and the other the 

 reverse. The effect of the poison on the robust specimen 

 consisted in depressing the pulsation, and reached its maximum 

 some fifteen minutes after application. But subsequently the 

 plant appeared to shake off the influence of the poison, and 

 the pulses slowly recovered, till in the course of an hour they 

 had once more become normal. The effect on the weakly 

 specimen, however, was somewhat different. Instead of 

 depression, the immediate result of application was a transi- 



