This same leaf had been observed 2 ½ months previously, and was then found to be oscillating or jerking.  We may therefore infer that this kind of movement goes on night and day for a very long period; and it is common to young unexpanded leaves and to leaves so old as to have lost their sensitiveness to a touch, but which were still capable of absorbing nitrogenous matter.  The phenomenon when well displayed, as in the young leaf just described, is a very interesting one.  It often brought before our minds the idea of effort, or of a small animal struggling to escape from some constraint.

(16.) Eucalyptus resinifera (Myrtaceae, Fam. 94).—­A young leaf, two inches in length together with the petiole, produced by a lateral shoot from a cut-down tree, was observed in the usual manner.  The blade had not as yet assumed its vertical position.  On June 7th only a few observations were made, and the tracing merely showed that the leaf had moved three times upwards and three downwards.  On the following day it was observed more frequently; and two tracings were made (see A and B, Fig. 108), as a single one would have been too complicated.  The apex changed its course 13 times in the course of 16 h., chiefly up and down, but with some lateral movement.  The actual amount of movement in any one direction was small.

Fig. 108.  Eucalyptus resinifera:  circumnutation of a leaf, traced, A, from 6.40 A.M. to 1 P.M.  June 8th; B, from 1 P.M. 8th to 8.30 A.M. 9th.  Apex of leaf 14 ½ inches from the horizontal glass, so figures considerably magnified.

(17.) Dahlia (garden var.) (Compositae, Fam. 122).—­A fine young [page 245] leaf 5 3/4 inches in length, produced by a young plant 2 feet high, growing vigorously in a large pot, was directed at an angle of about 45o beneath the horizon.  On June 18th the leaf descended from 10 A.M. till 11.35 A.M. (see Fig. 109); it then ascended greatly till 6 P.M., this ascent being probably due to the light

Fig. 109.  Dahlia:  circumnutation of leaf, traced from 10 A.M.  June 18th to 8.10 A.M. 20th, but with a break of 1 h. 40 m. on the morning of the 19th, as, owing to the glass filament pointing too much to one side, the pot had to be slightly moved; therefore the relative position of the two tracings is somewhat arbitrary.  The figure here given is reduced to one-fifth of the original scale.  Apex of leaf 9 inches from the glass in the line of its inclination, and 4 3/4 in a horizontal line. coming only from above.  It zigzagged between 6 P.M. and 10.35 P.M., and ascended a little during the night.  It should be remarked that the vertical distances in the lower part of the diagram are much exaggerated, as the leaf was at first deflected beneath the horizon, and after it had sunk downwards, the filament pointed in a very oblique line towards the glass.  Next [page 246] day the leaf descended from 8.20 A.M. till 7.15 P.M., then zigzagged and ascended greatly during the night.  On the morning of the 20th the leaf