CHAP. IV. DICOTYLEDONS. 243 



excluded. The apex sometimes crossed one or two divisions of 

 the micrometer at an imperceptibly slow rate, but generally it 

 moved onwards by rapid starts or jerks of y^ 2 ^ or yoVo* and in 

 one instance of y^^ of an inch. After each jerk forwards, the 

 apex drew itself backwards with comparative slowness for part 

 of the distance which had just been gained ; and then after a 

 very short time made another jerk forwards. Four conspi- 

 cuous jerks forwards, with slower retreats, were seen on one 

 occasion to occur in exactly one minute, besides some minor 

 oscillations. As far as we could judge, the advancing and 

 retreating lines did not coincide, and if so, extremely minute 

 ellipses were each time described. Sometimes the apex remained 

 quite motionless for a short period. Its general course during 

 the several hours of observation was in two opposite directions, 

 so that the leaf was probably circumnutating. 



An older leaf with the lobes fully expanded, and which was 

 afterwards proved to be highly sensitive to contact, was next 

 observed in a similar manner, except that the plant was exposed 

 to a lower temperature in a room. The apex oscillated forwards 

 and backwards in the same manner as before ; but the jerks for- 

 ward were less in extent, viz. about y^ inch ; and there were 

 longer motionless periods. As it appeared possible that the 

 movements might be due t4 currents of air, a wax taper was 

 held close to the leaf during one of the motionless periods, but 

 no oscillations were thus caused. After 10 m., however, vigorous 

 oscillations commenced, perhaps owing to the plant having been 

 warmed and thus stimulated. The candle was then removed and 

 before long the oscillations ceased ; nevertheless, when looked at 

 again after an interval of 1 h. 30 m., it was again oscillating. 

 The plant was taken back into the hot-house, and on the 

 following morning was seen to be oscillating, though not very 

 vigorously. Another old but healthy leaf, which was not in the 

 least sensitive to a touch, was likewise observed during two 

 days in the hot-house, and the attached filament made many 

 little jerks forwards of about y-^ or only y^o of an inch. 



Finally, to ascertain whether the lobes independently of the 

 petiole oscillated, the petiole of an old leaf was cemented close 

 to the blade with shellac to the top of a little stick driven into 

 the soil. But before this was done the leaf was observed, and 

 found to be vigorously oscillating or jerking ; and after it had 

 been cemented to the stick, the oscillations of about -r-^ of 

 an inch still continued. On the following day a little infusion 



