230 CIECUMNUTATION OF LEAVES. Chap, rv 



light in whicli it had long remained, and a filament was fixed 

 at the distance of '4 of an inch from the apex of a young leaf 

 nearly 4 inches in length. Its movements were then traced 

 during three days, but the tracing is not worth giving. The 

 leaf fell during the whole morning, and rose in the evening and 

 during the early part of the night. The ascending and descend- 

 ing lines did not coincide, so that an irregular ellipse was formed 

 each 24 h. The basal part of the midrib did not move, as was 

 ascertained by measuring at successive periods the angle which 

 it formed with the horizon, so that the movement was confined 

 to the terminal portion of the leaf, which moved through an 

 angle of IP in the course of 24 h., and the distance travelled by 

 the apex, up and down, was between ■ 8 and ■ 9 of an inch. 



In order to ascertain the effect of darkness, a filament was 

 fixed to a leaf oi inches in length, borne by a plant which after 

 forming a head had produced a stem. The leaf was inclined 

 44° above the horizon, and its movements were traced on a 

 vertical glass every hour by the aid of a taper. During the 

 first day the leaf rose from 8 a.m. to 10.40 p.m. in a slightly 

 zigzag course, the actual distance travelled by the apex being 

 ■ 67 of an inch. During the night the leaf fell, whereas it ought 

 to have risen ; and by 7 a.m. on the following morning it had 

 fallen -23 of an inch, and it continued falling until 9.40 a.m. It 

 then rose until 10.50 p m., but the rise was interrupted by one 

 considerable oscillation, that is, by a fall and re-ascent. During 

 the second night it again fell, but only to a very short distance, 

 and on the following morning re-ascended to a very short 

 distance. Thus the normal course of the leaf was greatly 

 disturbed, or rather completely inverted, by the absence of 

 light; and the movements were likewise greatly diminished in 

 amplitude. 



We may add that, according to Mr. A. Stephen Wilson,* the 

 young leaves of the Swedish turnip, which is a hybrid between 

 B. oleracea and rapa, draw together in the evening so much 

 "that the horizontal breadth diminishes about 30 per cent, of 

 the daylight breadth." Therefore the leaves must rise con- 

 siderably at night. 



(5.) Dianthus cai-yophyllus (Caryophyllese, Fam. 26). — The 



• ' Trans. Bot. Soo. Edinburgh,' see Darwin, ' Animals- and Plants 

 vol. xiii. p. 32. With resptct to under Domestication,' 2nd edit 

 the origin of the Swedish turnip, vol. i. p. 344. 



