218 



CmCUSiyUTATIOK OF LEAVES. 



Chap. 1^' 



Fig. 111. 



Dec. 5tli at at angle of 13' beneath the horizon, but by 9.30 p.m. 



the blade had straightened itsell 

 so much, which implies the 

 raising of the apex, that the 

 chord now stood at 37° above the 

 horizon, and had therefore risen 

 60°. On the next day similar 

 angular measurements of the 

 same leaf were made; and at 

 noon tlie chord stood 36° be- 

 neath the horizon, and 9.30 p.sl 

 3J° above it, so had risen 391°. 

 The chief cause of the rising 

 movement lies in the straighten- 

 ing of the bliide, but the short 

 petiole rises between 4° and .5°. 

 On the third night the chord 

 stood at 3.5° above the horizon, 

 and if the leaf occupied the 

 same position at noon, as on 

 the previous day, it had risen 

 71°. With older leaves no such 

 change of cui-vature could be 

 detected. The plant was then 

 brought into the house, and 

 kept in a north-east room, but 

 at night there was no change 

 in the curvature of the young 

 leaves; so that previous expo- 

 sure to a strong light is appa- 

 rently requisite for the jjeriodi- 

 cal change of curvature in the 

 blade, and for the slight rising 

 of the petiole. 



(21.) Wi'/iiwlia (Hydroleacea, 

 Fam. 149).— Professor Pfeffer 

 informs us that the leaves of this 

 plant rise in the evening ; but as 

 we do not know whether or not 

 the rising is grciit, this species 

 ought i^erhaps to be classed 

 amongst sleeping plants 



Petunia viol '(X '- : downward more- 

 ment and circnmnutation of a 

 xtTj young leaf, traced from 10 

 A.M. June 2nd to 9.20 A.M. June 

 6th. >i'.B. — At 6.40 A.5L on tne 

 5th it was necessary to move the 

 pot a little, and a new tr.icing 

 was begun at the point where 

 two dots are not joined in trie 

 diagram. Apex of leaf 7 inches 

 from the vei tical glass. Temp, 

 generally 17J°C. 



