Botany; Geotropism; Plants -- Irritability and movements
(11.) Hedera helix (Araliaceae, Fam. 114).—The stem is known to be
apheliotropic, and several seedlings growing in a pot in the greenhouse
became bent in the middle of the summer at right angles from the light.
On Sept. 2nd some of these stems were tied up so as to stand
vertically, and were placed before a north-east window; but to our
surprise they were now decidedly heliotropic, for during 4 days they
curved themselves towards the light, and their course being traced on a
horizontal glass, was strongly zigzag. During the 6 succeeding days
they circumnutated over the same small space at a slow rate, but there
could be no doubt about their circumnutation. The plants were kept
exactly in the same place before the window, and after an interval of
15 days the stems were again observed during 2 days and their movements
traced, and
they were found to be still circumnutating, but on a yet smaller scale.
(12.) Gazania ringens (Compositæ, Fam. 122).—The circumnutation of the
stem of a young plant, 7 inches in height, as measured to the tip of
the highest leaf, was traced during 33 h., and is shown in the
accompanying figure (Fig. 78). Two main lines may be observed running
at nearly right angles to two other main lines; but these are
interrupted by small loops.
Fig. 78. Gazania ringens: circumnutation of stem traced from 9 A.M.
March 21st to 6 P.M. on 22nd; plant kept in darkness. Movement of bead
at the close of the observations magnified 34 times, here reduced to
half the original scale.
(13.) Azalea Indica (Ericineae, Fam. 128).—A bush 21 inches in height
was selected for observation, and the circumnutation of its leading
shoot was traced during 26 h. 40 m., as shown in the following figure
(Fig. 79).
(14.) Plumbago Capensis (Plumbagineae, Fam. 134).—A small lateral
branch which projected from a tall freely growing bush, at an angle of
35° above the horizon, was selected for observation. For the first 11
h. it moved to a considerable distance in a nearly straight line to one
side, owing probably to its having been previously deflected by the
light whilst standing in the greenhouse. At 7.20 P.M. on March 7th a
fresh tracing was begun and continued for the next 43 h. 40 m. (see
Fig. 80). During the first 2 h. it followed nearly the same direction
as before, and then changed it a little; during the night it moved at
nearly right angles to its previous course. Next
day (8th) it zigzagged greatly, and on the 9th moved irregularly round
and round a small circular space. By 3 P.M. on the 9th the figure had
become so complicated that no more dots could be made; but the shoot
continued during the evening of the 9th, the whole of the 10th, and the
morning of the 11th to circumnutate over the same small space, which
was only about the 1/26th of an inch (.97 mm.) in diameter. Although
this branch circumnutated to a very small extent, yet it changed its
course frequently. The movements ought to have been more magnified.
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