CHAPTER XXI 



THE AUTOMATIC PULSATIONS OF DESMODIUM GYRANS 



Activity of detached leaflet of Desmodium — Pulsation maintained uniform 

 under constant internal hydrostatic pressure — The plant chamber— 

 Time-relations of pulsating movement derived from dotted record — 

 Significance of down and up movements — Systole and diastole — 

 Table showing rates of movement of Desmodium leaflet at different 

 phases. 



We have hitherto studied the responsive movement in 

 sensitive plants, where such movement was initiated by 

 a directly exciting stimulus. We shall now take up the 

 consideration of another class of move- 

 ments, which are apparently auto- 

 matic or without any immediately 

 preceding cause. In certain plants we 

 observe what are known as spontane- 

 ous movements, of which Desmodium 

 gyrans or the telegraph-plant fur- 

 nishes an example. 



This telegraph-plant grows wild 

 in the Gangetic plain ; its Indian 

 name is Bon Char at, or ' forest churl,' 

 the popular belief being that it 

 dances to the clapping of the hands. 

 There is, however, no foundation 

 for this belief. It is a papilionaceous 

 plant with trifoliate leaves, of which the terminal leaflet 

 is large, and the two lateral, very small (fig. 140). 

 Each of these is inserted on the petiole by means of 

 pulvinule. The lateral leaflets are seen to execute pulsating 

 movements which are apparently uncaused, and are not 



290 



Fig. 140. — Leaf of Des- 

 modium gyrans. The 

 two small lateral 

 leaflets exhibit spon- 

 taneous movements. 



