Botany; Geotropism; Plants -- Irritability and movements
In order to prove that there was circumnutation, the movements of five
seedlings, varying in height from .3 inch to 2 inches, were traced.
They were placed within a box and illuminated from above; but in all
five cases the longer axes of the figures described were directed to
nearly the same point; so that more light seemed to have come through
the glass roof of the greenhouse on one side than on any other. All
five tracings resembled each other to a certain extent, and it will
suffice to give two of them. In A (Fig. 48) the seedling was only .45
of an
inch in height, and consisted of a single internode bearing a bud on
its summit. The apex described between 8.30 A.M. and 10.20 P.M. (i.e.
during nearly 14 hours) a figure which would probably have consisted of
3½ ellipses, had not the stem been drawn to one side until 1 P.M.,
after which hour it moved backwards. On the following morning it was
not far distant from the point whence it had first started. The actual
amount of movement of the apex from side to side was very small, viz.
about 1/18th of an inch. The seedling of which the movements are shown
in Fig. 48, B, was 1 3/4 inch in height, and consisted of three
internodes besides the bud on the summit. The figure, which was
described during 10 h., apparently represents two irregular and unequal
ellipses or circles. The actual amount of movement of the apex, in the
line not influenced by the light, was .11 of an inch, and in that thus
influenced .37 of an inch. With a seedling 2 inches in height it was
obvious, even without the aid of any tracing, that the uppermost part
of the stem bent successively to all points of the compass, like the
stem of a twining plant. A little increase in the power of
circumnutating and in the flexibility of the stem, would convert the
common asparagus into a twining plant, as has occurred with one species
in this genus, namely, A. scandens.
Fig. 48. Asparagus officinalis: circumnutation of plumules with tips
whitened and marks placed beneath, traced on a horizontal glass. A,
young plumule; movement traced from 8.30 A.M. Nov. 30th to 7.15 A.M.
next morning; magnified about 35 times. B, older plumule; movement
traced from 10.15 A.M. to 8.10 P.M. Nov. 29th; magnified 9 times, but
here reduced to one-half of original scale.
Phalaris Canariensis (Gramineæ).—With the Gramineæ the part which first
rises above the ground has been called by some authors the pileole; and
various views have been expressed on its homological nature. It is
considered by some great authorities to be a cotyledon, which term we
will use without venturing to express any opinion on the subject.[6] It
consists in the present case of a slightly flattened reddish sheath,
terminating upwards in a sharp white edge; it encloses a true green
leaf, which protrudes from the sheath through a slit-like orifice,
close beneath and at right angles to the sharp edge on the summit. The
sheath is not arched when it breaks through the ground.
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