C YRA TION OF PLA NTS. 1 61 



marked diurnal movements, rising in the evening and 

 falling during the latter part of the night, or early 

 morning, whilst during the middle of the day they 

 rotate around the same small space. 



More complex movements take place in Venus's Fly- 

 trap (Dionced). In a young state the two lobes of 

 the leaf are pressed closely together. In the evening 

 one of these young leaves formed an ellipse in the 

 course of two hours. An older leaf did not rotate 

 plainly. A young and unexpanded leaf was care- 

 fully watched with a micrometer. It moved onwards 

 generally by rapid jerks. After each jerk the apex 

 drew itself backwards slowly for part of the distance 

 that it had advanced, and then, slowly afterwards, 

 made another jerk forwards. Four conspicuous jerks 

 forwards, with slower retreats, were on one occasion 

 seen to occur in exactly one minute. Sometimes the 

 apex remained quite motionless for a short period. 

 An older leaf was tested in a similar manner at a 

 lower temperature, the apex oscillated forwards and 

 backwards in the same way, but the jerks forward 

 were less, and the motionless periods longer. During 

 one of these motionless periods a wax taper was held 

 close to the leaf. After ten minutes violent oscilla- 

 tions commenced, perhaps owing to the stimulus of 

 the warmth of the taper. The light was then re- 

 moved, and in a short time the oscillations ceased. 

 Looked at again after a period of an hour and a 



M 



