CHAPTER XXV 



INFLUENCE OF VARIOUS CHEMICAL REAGENTS ON THE 

 AUTONOMOUS RESPONSE OF DESMODIUM GYRANS 



The recorder and experimental chamber — Absolute measurement of period and 

 amplitude of Desmod/2/m-osciWa.tion — Responsive significance of up and down 

 movements deduced from (a) analogy with response of Mimosa ; (b) test of 

 increased internal hydrostatic pressure — • Systolic' contraction and ' diastolic' 

 expansion of Desmodhtm pulvinus — Mode of application of chemical reagents 

 — Action of chemical reagents modified by : tonic condition of plants ; strength 

 of solution ; and duration of application — Effect of anaesthetics — Effect of 

 alcohol — Effect of carbonic acid — Effects of ammonia and of carbon disul- 

 phide — Effect of copper sulphate solution, either when applied externally, 

 direct on the pulvinus, or internally — Spark-record of Desmodium- pulsation. 



Having thus, in the last chapter, traced the causes of 

 autonomous movements in plants, I shall now, taking Desmo- 

 dium gyrans as the type, describe the effect of various 

 agencies on the so-called ' spontaneous ' responses of its 

 lateral leaflets. 



With regard to the experimental arrangements for 

 making the record, I have already in Chapter I. described 

 how records may be obtained, using the intact plant for 

 experiment. The automatic movements of the leaflets, how- 

 ever, persist, even after the petiole bearing them is detached, 

 the cut end being kept in water. Under proper conditions, 

 the rhythmic pulsations of the detached specimen will continue 

 for a couple of days. In order, therefore, to subject the motile 

 organ to various modifying conditions, it is much more con- 

 venient to use such a specimen than the whole plant. 



The recorder and experimental chamber. — As the 

 extent of the movement of the tip of the leaflet is consider- 

 able, no magnification is necessary for the record. A single 

 cocoon thread is attached to the middle of the leaflet by a 



