248 



CIKCUMNUTATION OF LEAVES. 



CHAP. 17 



Doc. 5th at an angle of 13 beneath the horizon, but by 9.30 P.M, 



the blade had straightened itself 



Fl S- 111% so much, which implies the 



\raising of the apex, that the 

 chord now stood at 37 above the 

 horizon, and had therefore risen 

 - 50. On the next day similar 



angular measurements of the 

 same leaf were made; and at 

 noon the chord stood 36 be- 

 neath the horizon, and 9.30 P.M. 

 3J above it, so had risen 39J. 

 The chief cause of the rising 

 movement lies in the straighten- 

 ing of the blade, but the short 

 petiole rises between 4 and 5. 

 On the third night the chord 

 stood at 35 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 curvature 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 

 4. in the curvature of the young 



y<\ leaves; so that previous expo- 



/ *^^ sure to a strong light is appa- 



^~-~w7 rently requisite for the periodi- 



vj cal change of curvature in the 



blade, and for the slight rising 

 Frfwma violacea : downward move- ' 



ment and circumnutation of a of the petiole, 

 rery young leaf, traced from 10 (21.) Wigandia (HydroleaceJB, 



ery yo 

 .M. Ju 



informs us that the leaves of this 



6th. N.B. At 6.40 A.M. on the 



5th it was necessary to move the 



pot a little, and a new tracing plant rise in the evening; but as 



was begun at the point where \ye do not know whether or not 



two dots are not joined in the ^ rising ig g^ tMg gpeciea 



diagram. Apex of leaf 7 inches v v i x 



from the vertical glass. Temp. OUght perhaps to be classed 



generally 17J C. amongst sleeping plants. 



