34Q 



PLANT RESPONSE 



in the case of cardiac pulsation, it is possible that one appa- 

 rently simple contraction may in reality consist of several, 

 which are rendered indistinguishable by the great rapidity 

 of their succession. 



Now, since the pulsatory response of Desmodiutn is in 

 every way so similar to that of cardiac muscle, its analysis 

 might be expected to throw much light on this question ; 

 and this more especially since it possesses the added advantage 

 that its pulsation is executed in a period about one hundred 

 times as long as that of cardiac muscle. The constituent 



elements of each pulsation, if such 

 exist, ought thus, owing to the 

 relative slowness of the movement, 

 to be much more easy of detection. 

 Now, it is often seen in watching 

 the pulsatory movements of Des- 

 modium that they proceed some- 

 what discontinuously, or by jerks. 

 Under favourable circumstances, 

 nevertheless, the movements of 

 the leaflet up and down become 

 apparently continuous. When 

 such pulsations are recorded on a 

 rather rapidly moving drum, the 

 discrete nature of the movement 

 can be brought out more easily in 

 the case of the up movement, which is relatively slow. This 

 is shown in a very interesting manner in the accompanying 

 photographic record (fig. 142), where the subsidiary pulsations 

 make themselves visible as nodules ; places where the move- 

 ment is slow appear thicker, on account of the photographic 

 irradiation-effect. During the course of the single up move- 

 ment recorded in this photograph, we may count as many as 

 twenty-five of these sub-pulses. It has been said that these 

 subsidiary movements are more easily detected when the 

 general movement is relatively slow ; and in connection with 

 this it is extremely interesting to note the record of pulsations 



FlG. 142. Photographic Record 

 of Pulsation of Desmodium, 

 showing Sub-pulses during 

 slower Up Movement, as 

 Nodules 



