CHAP. VII. SLEEP OF LEAVES. 387 



have their longer axes differently directed from the cells of the 

 parenchyma, and may therefore be considered as forming a sort 

 of pulvinus. A young plant of N. tabacum was selected, and 

 the circumnutation of the fifth leaf above the cotyledons was 

 observed during three days. On the first morning (July 10th) 

 the leaf fell from 9 to 10 A.M., which is its normal course, but 

 rose during the remainder of the day ; and this no doubt was 

 due to its being illuminated exclusively from above; for properly 

 the evening rise does not commence until 3 or 4 P.M. In the 

 figure as given on p. 386 (Fig. 163) the first dot was made at 

 3 P.M. ; and the tracing was continued for the following 65 h. 

 When the leaf pointed to the dot next above that marked 3 P.M., 

 it stood horizontally. The tracing is remarkable only from its 

 simplicity and the straightness of the lines. The leaf each day 

 described a single great ellipse ; for it should be observed that 

 the ascending and descending lines do not coincide. On the 

 evening of the llth the leaf did not descend quite so low as 

 usual, and it now zigzagged a little. The diurnal sinking move- 

 ment had already commenced each morning by 7 A.M. The broken 

 lines at the top of the figure, representing the nocturnal vertical 

 position of the leaf, ought to be prolonged much higher up. 



Mirabitts longiflora and jalapa (Nyctagineae). The first pair 

 of leaves above the cotyledons, produced by seedlings of both 

 these species, were considerably divergent during the day, and 

 at night stood up vertically in close contact with one another. 

 The two upper leaves on an older seedling were almost horizontal 

 by day, and at night stood up vertically, but were not in close 

 contact, owing to the resistance offered by the central bud. 



Polygonum aviculare (Polygonese). Professor Batalin informs 

 us that the young leaves rise up vertically at night. This is 

 likewise the case, according to Linnaeus, with several species 

 of Amaranthus (Amaranthacese) ; and we observed a sleep move- 

 ment of this kind in one member of the genus. Again, with 

 Chenopodium album (Chenopodieae), the upper young leaves of, 

 some seedlings, about 4 inches in height, were horizontal or 

 sub-horizontal during the day, and at 10 P.M. on March 7th 

 were quite, or almost quite, vertical. Other seedlings raised in 

 the greenhouse during the winter (Jan. 28th) were observed day 

 and night, and no difference could be perceived in the position 

 of their leaves. According to Bouche (' Bot. Zeitung/ 1874, 

 p. 359; the leaves of Pimdia, linoides and spectabilis (Thymelese) 

 sleep at night. 



