CHAP. VII. 



SLEEP OF LEAVES. 



379 



although the proper order of their movements in relation to the 

 day and night was wholly lost. Thus, one leaf descended during 

 the first two nights (i.e. between 10 P.M. and 7 A.M. next morn- 

 ing) instead of ascending, and on the third night it moved 

 chiefly in a lateral direction. The second leaf behaved in an 

 equally abnormal manner, moving laterally during the first 

 night, descending greatly during the second, and ascending to 

 an unusual height during the third night. 



With plants kept at a high temperature and exposed to the 

 light, the most rapid circumnutating movement of the apex 

 of a leaf which was observed, amounted to ^^ of an inch in 

 one second; and this would have equalled of an inch in a 

 minute, had not the leaf occasionally stood still. The actual 

 distance travelled by the apex (as ascertained by a measure 

 placed close to the leaf) was on one occasion nearly f of an inch 

 in a vertical direction in 15 m. ; and on another occasion -g- of an 

 inch in 60 m. ; but there was also some lateral movement. 



Mimosa albida* The leaves of this plant, one of which is here 

 figured (Fig. 159) reduced to f of the natural size, present some 



Fig. 159. 



Mimosa albida : leaf seen from vertically above. 



interesting peculiarities. It consists of a long petiole bearing 

 only two pinnae (here represented as rather more divergent 

 than is usual), each with two pairs of leaflets. But the inner 



* Mr. Thistleton Dyer informs 

 us that this Peruvian plant (which 

 was sent to us from Kew) is con- 

 sidered by Mr. Bentham (' Trans. 



Linn. Soc.,' vol. xxx. p. 390) to 

 be " the species or variety which 

 most commonly represents the M. 

 sensitiva of our gardens." 



