240 



CIBCUMNUTATION OF LEAVES. 



Chap. IV 



Fig. 106. 



petiole was only 1'2 inch, in length, had a filament fixed exter- 

 nally along the midrib of the still closed lobes, which projected 

 at right angles to the petiole. In the evening this leaf com- 

 pleted an ellipse in the course of 2 h. On 

 the following day (Sept. 25th) its move- 

 ments were traced during 22 h. ; and we 

 see in Kg. 106 that it moved in the same 

 general direction, due to the straightening 

 of the leaf, but in an extremely zigzag line. 

 This line represents several drawn-out or 

 modified ellipses. There can therefore be 

 no doubt that this young leaf circumnu- 

 tated. 



A rather old, horizontally extended 

 leaf, with a filament attached along the 

 under side of the midrib, was next 

 observed during 7 h. It hardly moved, 

 but when one of its sensitive hairs 

 was touched, the blades closed, though 

 not very quickly. A new dot was now 

 made on the glass, but in the course of 

 14 h. 20 m. there was hardly any change 

 in the position of the filament. We may 

 therefore infer that an old and only 

 moderately sensitive leaf does not circitm- 

 nutate plainly; but we shall soon see 

 that it by no means follows that such 

 a leaf is absolutely motionless. We may 

 further infer that the stimulus from a 

 touch does not re-excite plain circumnu- 

 tation. 



Another full-grown leaf had a filament 

 attached externally along one side of the 

 midrib and parallel to it, so that the filar 

 ment would move if the lobes closed. It 

 should be first stated that, although a touch on one of the sensi- 

 tive hairs of a vigorous leaf causes it to close quickly, often 

 almost instantly, yet when a bit of damp meat or some solution 

 of carbonate of ammonia is placed on the lobes, they close so 

 slowly that generally 24 h. is required for the completion of the 

 act. The above leaf was first observed for 2 h. 30 m., and did 

 not circnmnutate, but it ought to have been observed for a 



Doncea muscipuia : cir- 

 cumnutation of a 

 young and expanding 

 leaf, traced on a hori- 

 zontal sflass in dark- 

 ness, from noon Sept. 

 24th to 10 A.M. 25th. 

 Apex of leaf ISJ 

 inches from the glass, 

 so tracing consider- 

 ably magnified. 



