CHEMICAL REAGENTS ON AUTONOMOUS PULSATION 



17 



introduced into the chamber for any desired length of time, 

 after which fresh air may be re-introduced. In order to 

 produce variations of temperature there is a coil of wire for 

 electric heating. 



The automatic movements of the leaflet, both up and 

 down, take place in some cases as a number of jerks, which 

 may pass gradually into continuous movement. In others 

 they are continuous from the beginning. From the normal 

 or highest position, the leaflet, generally speaking, sinks some- 

 what rapidly. Having reached its maximum depressed position, 

 there is a pause, after which there is rather a slow return to 

 its original position. The up and down motion is in some 

 cases approximately straight. In other cases, the sub-petiole 

 of the leaflet is slightly twisted after its descent, and the 

 curve described becomes more circular. For the purpose of 

 the present investigation, specimens were selected in which 

 the movement of the leaflet took place gradually, without 

 jerks, the up and down move- 

 ments being approximately in a 

 straight line. 



Absolute measurement of 

 period and amplitude of Des- 

 modium - oscillation. — The 



period of a single oscillation 

 varies with the temperature and 

 the tonic condition of the plant. 

 In winter it may be as long as 

 five, in summer as short as two 

 minutes, and when the tempera- 

 ture is artificially raised, the 

 period may be even further re- 

 duced to one minute. As a con- 

 crete example, affording a clear 

 idea of the general characteristics 



of the pulsatory movement of Desmodium, I shall give 

 the following results, obtained from a photographic record 

 which gives the extent of the absolute movement (fig. 126). 



Eig. 126. Photographic Record of 

 Pulsation of Desmodium 



The up movement of the record 

 means down movement of the 

 leaflet in this and all subsequent 

 records. 



