In order to ascertain the effect of darkness, a filament was fixed to a leaf 5 ½ inches in length, borne by a plant which after forming a head had produced a stem.  The leaf was inclined 44o 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 considerably at night.

(5.) Dianthus caryophyllus (Caryophylleae, Fam. 26).—­The

* ‘Trans.  Bot.  Soc.  Edinburgh,’ vol. xiii. p. 32.  With respect to the origin of the Swedish turnip, see Darwin, ’Animals and Plants under Domestication,’ 2nd edit. vol. i. p. 344. [page 231]

terminal shoot of a young plant, growing very vigorously, was selected for observation.  The young leaves at first stand up vertically and close together, but they soon bend outwards and downwards, so as to become horizontal, and often at the same time a little to one side.  A filament was fixed to the tip of a young leaf whilst still highly inclined, and the first dot was made on the vertical glass at 8.30 A.M.  June 13th, but it curved downwards so quickly that by 6.40 A.M. on the following morning it stood only a little above the horizon.  In Fig. 96

Fig. 96.  Dianthus caryophyllus:  circumnutation of young leaf, traced from 10.15 P.M.  June 13th to 10.35 P.M. 16th.  Apex of leaf stood, at the close of our observations, 8 3/4 inches from the vertical glass, so tracing not greatly magnified.  The leaf was 5 1/4 inches long.  Temp. 15 1/2o — 17 1/2o C.

the long, slightly zigzag line representing this rapid downward course, which was somewhat inclined to the left, is not given; but the figure shows the highly tortuous and zigzag course, together with some loops, pursued during the next 2 ½ days.  As the leaf continued to move all the time to the left, it is evident that the zigzag line represents many circumnutations.