Circumnutation of leaves:  Dicotyledons.

Several distinguished botanists, Hofmeister, Sachs, Pfeffer, De Vries,
Batalin, Millardet, etc., have ob-

* ‘Jenaische Zeitsch.,’ B. v. p. 133.

** ‘N.  Mem. de l’Acad.  R. de Bruxelles,’ tom. xiv. 1841, p. 3.

*** ‘Sitzungbericht des bot.  Vereins der P. Brandenburg,’ xxi. p. 84. [page 227] served, and some of them with the greatest care, the periodical movements of leaves; but their attention has been chiefly, though not exclusively, directed to those which move largely and are commonly said to sleep at night.  From considerations hereafter to be given, plants of this nature are here excluded, and will be treated of separately.  As we wished to ascertain whether all young and growing leaves circumnutated, we thought that it would be sufficient if we observed between 30 and 40 genera, widely distributed throughout the vegetable series, selecting some unusual forms and others on woody plants.  All the plants were healthy and grew in pots.  They were illuminated from above, but the light perhaps was not always sufficiently bright, as many of them were observed under a skylight of ground-glass.  Except in a few specified cases, a fine glass filament with two minute triangles of paper was fixed to the leaves, and their movements were traced on a vertical glass (when not stated to the contrary) in the manner already described.  I may repeat that the broken lines represent the nocturnal course.  The stem was always secured to a stick, close to the base of the leaf under observation.  The arrangement of the species, with the number of the Family appended, is the same as in the case of stems.

Fig. 93.  Sarracenia purpurea:  circumnutation of young pitcher, traced from 8 A.M.  July 3rd to 10.15 A.M. 4th.  Temp. 17o — 18o C. Apex of pitcher 20 inches from glass, so movement greatly magnified.

(1.) Sarracenia purpurea (Sarraceneae, Fam. 11).—­A young leaf, or pitcher, 8 ½ inches in height, with the bladder swollen but with the hood not as yet open, had a filament fixed transversely [page 228] across its apex; it was observed for 48 h., and during the whole of this time it circumnutated in a nearly similar manner, but to a very small extent.  The tracing given (Fig. 93) relates only to the movement during the first 26 h.

(2) Glaucium luteum (Papaveraceae, Fam. 12).—­A young plant, bearing only 8 leaves, had a filament attached to the youngest leaf but one, which was 3 inches in length, including the petiole.  The circumnutating movement was traced during 47 h.  On both days the leaf descended from before 7 A.M. until about 11 A.M., and then ascended slightly during the rest of the day and the early part of the night.  During the latter part of the night it fell greatly.  It did not ascend so much during the second as during the first day, and it descended considerably lower on the second night than on the first.  This difference was probably due to the illumination from above having been insufficient during the two days of observation.  Its course during the two days is shown in Fig. 94.