Botany; Geotropism; Plants -- Irritability and movements
of the abruptly curved portion of the growing stem of this plant, which
appears to be wholly due to hyponasty, is the result of modified
circumnutation. We will only add that a filament was fixed in a
different manner across the curved summit of another plant, and the
same general kind of movement was observed.
Trifolium repens.—In many, but not in all the species of Trifolium, as
the separate little flowers wither, the sub-peduncles bend downwards,
so as to depend parallel to the upper part of the main peduncle. In Tr.
subterraneum the main peduncle curves downwards for the sake of burying
its capsules, and in this species the sub-peduncles of the separate
flowers bend
upwards, so as to occupy the same position relatively to the upper part
of the main peduncle as in Tr. repens. This fact alone would render it
probable that the movements of the sub-peduncles in Tr. repens were
independent of geotropism. Nevertheless, to make sure, some
flower-heads were tied to little sticks upside down and others in a
horizontal position; their sub-peduncles, however, all quickly curved
upwards through the action of heliotropism. We therefore protected some
flower-heads, similarly secured to sticks, from the light, and although
some of them rotted, many of their sub-peduncles turned very slowly
from their reversed or from their horizontal positions, so as to stand
in the normal manner parallel to the upper part of the main peduncle.
These facts show that the movement is independent of geotropism or
apheliotropism; it must there[fore] be attributed to epinasty, which
however is checked, at least as long as the flowers are young, by
heliotropism. Most of the above flowers were never fertilised owing to
the exclusion of bees; they consequently withered very slowly, and the
movements of the sub-peduncles were in like manner much retarded.
Fig. 124. Trifolium repens: circumnutating and epinastic movements of
the sub-peduncle of a single flower, traced on a vertical glass under a
skylight, in A from 11.30 A.M. Aug. 27th to 7 A.M. 30th; in B from 7
A.M. Aug. 30th to a little after 6 P.M. Sept. 8th.
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