MODIFIED CIRCUMNUTATION: CLIMBING PLANTS; EPINASTIC AND HYPONASTIC
MOVEMENTS.
Circumnutation modified through innate causes or through the action of
external conditions—Innate causes—Climbing plants; similarity of their
movements with those of ordinary plants; increased amplitude;
occasional points of difference—Epinastic growth of young
leaves—Hyponastic growth of the hypocotyls and epicotyls of
seedlings—Hooked tips of climbing and other plants due to modified
circumnutation—Ampelopsis tricuspidata—Smithia Pfundii—Straightening of
the tip due to hyponasty—Epinastic growth and circumnutation of the
flower-peduncles of Trifolium repens and Oxalis carnosa.
The radicles, hypocotyls and epicotyls of seedling plants, even before
they emerge from the ground, and afterwards the cotyledons, are all
continually circumnutating. So it is with the stems, stolons,
flower-peduncles, and leaves of older plants. We may, therefore, infer
with a considerable degree of safety that all the growing parts of all
plants circumnutate. Although this movement, in its ordinary or
unmodified state, appears in some cases to be of service to plants,
either directly or indirectly—for instance, the circumnutation of the
radicle in penetrating the ground, or that of the arched hypocotyl and
epicotyl in breaking through the surface—yet circumnutation is so
general, or rather so universal a phenomenon, that we cannot suppose it
to have been gained for any special purpose. We must believe that it
follows in some unknown way from the manner in which vegetable tissues
grow.
We shall now consider the many cases in which circumnutation has been
modified for various special purposes; that is, a movement already in
progress is temporarily increased in some one direction, and
temporarily diminished or quite arrested in other directions. These
cases may be divided in two sub-classes; in one of which the
modification depends on innate or constitutional causes, and is
independent of external conditions, excepting in so far that the proper
ones for growth must be present. In the second sub-class the
modification depends to a large extent on external agencies, such as
the daily alternations of light and darkness, or light alone,
temperature, or the attraction of gravity. The first small sub-class
will be considered in the present chapter, and the second sub-class in
the remainder of this volume.
THE CIRCUMNUTATION OF CLIMBING PLANTS.
The simplest case of modified circumnutation is that offered by
climbing plants, with the exception of those which climb by the aid of
motionless hooks or of rootlets: for the modification consists chiefly
in the greatly increased amplitude of the movement. This would follow
either from greatly increased growth over a small length, or more
probably from moderately increased growth spread over a considerable
length of the moving organ, preceded by turgescence, and acting
successively on all sides. The circumnutation of climbers is more
regular than that of ordinary plants; but in almost every other respect
there is a close similarity between their movements, namely, in their
tendency to describe ellipses directed successively to all points of
the compass—in their courses being often interrupted by zigzag lines,
triangles, loops, or small
ellipses—in the rate of movement, and in different species revolving
once or several times within the same length of time. In the same
internode, the movements cease first in the lower part and then slowly
upwards. In both sets of cases the movement may be modified in a
closely analogous manner by geotropism and by heliotropism; though few
climbing plants are heliotropic. Other points of similarity might be
pointed out.
That the movements of climbing plants consist of ordinary
circumnutation, modified by being increased in amplitude, is well
exhibited whilst the plants are very young; for at this early age they
move like other seedlings, but as they grow older their movements
gradually increase without undergoing any other change. That this power
is innate, and is not excited by any external agencies, beyond those
necessary for growth and vigour, is obvious. No one doubts that this
power has been gained for the sake of enabling climbing plants to
ascend to a height, and thus to reach the light. This is effected by
two very different methods; first, by twining spirally round a support,
but to do so their stems must be long and flexible; and, secondly, in
the case of leaf-climbers and tendril-bearers, by bringing these organs
into contact with a support, which is then seized by the aid of their
sensitiveness. It may be here remarked that these latter movements have
no relation, as far as we can judge, with circumnutation. In other
cases the tips of tendrils, after having been brought into contact with
a support, become developed into little discs which adhere firmly to
it.
We have said that the circumnutation of climbing plants differs from
that of ordinary plants chiefly by its greater amplitude. But most
leaves circumnutate
in an almost vertical plane, and therefore describe very narrow
ellipses, whereas the many kinds of tendrils which consist of
metamorphosed leaves, make much broader ellipses or nearly circular
figures; and thus they have a far better chance of catching hold of a
support on any side. The movements of climbing plants have also been
modified in some few other special ways. Thus the circumnutating stems
of Solnanum dulcamara can twine round a support only when this is as
thin and flexible as a string or thread. The twining stems of several
British plants cannot twine round a support when it is more than a few
inches in thickness; whilst in tropical forests some can embrace thick
trunks;[1] and this great difference in power depends on some unknown
difference in their manner of circumnutation. The most remarkable
special modification of this movement which we have observed is in the
tendrils of Echinocystis lobata; these are usually inclined at about
45° above the horizon, but they stiffen and straighten themselves so as
to stand upright in a part of their circular course, namely, when they
approach and have to pass over the summit or the shoot from which they
arise. If they had not possessed and exercised this curious power, they
would infallibly have struck against the summit of the shoot and been
arrested in their course. As soon as one of these tendrils with its
three branches begins to stiffen itself and rise up vertically, the
revolving motion becomes more rapid; and as soon as it has passed over
the point of difficulty, its motion coinciding with that from its own
weight, causes it to fall into its previously inclined position so
quickly, that the apex can be seen travelling like the hand of a
gigantic clock.
[1] ‘The Movements and Habits of Climbing Plants,’ p. 36.
A large number of ordinary leaves and leaflets and a few
flower-peduncles are provided with pulvini; but this is not the case
with a single tendril at present known. The cause of this difference
probably lies in the fact, that the chief service of a pulvinus is to
prolong the movement of the part thus provided after growth has ceased;
and as tendrils or other climbing-organs are of use only whilst the
plant is increasing in height or growing, a pulvinus which served to
prolong their movements would be useless.
It was shown in the last chapter that the stolons or runners of certain
plants circumnutate largely, and that this movement apparently aids
them in finding a passage between the crowded stems of adjoining
plants. If it could be proved that their movements had been modified
and increased for this special purpose, they ought to have been
included in the present chapter; but as the amplitude of their
revolutions is not so conspicuously different from that of ordinary
plants, as in the case of climbers, we have no evidence on this head.
We encounter the same doubt in the case of some plants which bury their
pods in the ground. This burying process is certainly favoured by the
circumnutation of the flower-peduncle; but we do not know whether it
has been increased for this special purpose.
EPINASTY—HYPONASTY.
The term epinasty is used by De Vries[2] to express greater
longitudinal growth along the upper than
along the lower side of a part, which is thus caused to bend downwards;
and hyponasty is used for the reversed process, by which the part is
made to bend upwards. These actions come into play so frequently that
the use of the above two terms is highly convenient. The movements thus
induced result from a modified form of circumnutation; for, as we shall
immediately see, an organ under the influence of epinasty does not
generally move in a straight line downwards, or under that of hyponasty
upwards, but oscillates up and down with some lateral movement: it
moves, however, in a preponderant manner in one direction. This shows
that there is some growth on all sides of the part, but more on the
upper side in the case of epinasty, and more on the lower side in that
of hyponasty, than on the other sides. At the same time there may be in
addition, as De Vries insists, increased growth on one side due to
geotropism, and on another side due to heliotropism; and thus the
effects of epinasty or of hyponasty may be either increased or
lessened.
[2] ‘Arbeiten des Bot. Inst., in Würzburg,’ Heft ii. 1872, p. 223. De
Vries has slightly modified (p. 252) the meaning of the above two
terms as first used by Schimper, and they have been adopted in this
sense by Sachs.
He who likes, may speak of ordinary circumnutation as being combined
with epinasty, hyponasty, the effects of gravitation, light, etc.; but
it seems to us, from reasons hereafter to be given, to be more correct
to say that circumnutation is modified by these several agencies. We
will therefore speak of circumnutation, which is always in progress, as
modified by epinasty, hyponasty, geotropism, or other agencies, whether
internal or external.
One of the commonest and simplest cases of epinasty is that offered by
leaves, which at an early age are crowded together round the buds, and
diverge as they grow older. Sachs first remarked that this was due to
increased growth along the upper side of the petiole and blade; and De
Vries has now shown in more detail that the movement is thus caused,
aided slightly by
the weight of the leaf, and resisted as he believes by apogeotropism,
at least after the leaf has somewhat diverged. In our observations on
the circumnutation of leaves, some were selected which were rather too
young, so that they continued to diverge or sink downwards whilst their
movements were being traced. This may be seen in the diagrams (Figs. 98
and 112, pp. 232 and 249) representing the circumnutation of the young
leaves of Acanthus mollis and Pelargonium zonale. Similar cases were
observed with Drosera. The movements of a young leaf, only 3/4 inch in
length, of Petunia violacea were traced during four days, and offers a
better instance (Fig. 111, p. 248) as it diverged during the whole of
this time in a curiously zigzag line with some of the angles sharply
acute, and during the latter days plainly circumnutated. Some young
leaves of about the same age on a plant of this Petunia, which had been
laid horizontally, and on another plant which was left upright, both
being kept in complete darkness, diverged in the same manner for 48 h.,
and apparently were not affected by apogeotropism; though their stems
were in a state of high tension, for when freed from the sticks to
which they had been tied, they instantly curled upwards.
The leaves, whilst very young, on the leading shoots of the Carnation
(Dianthus caryophyllus) are highly inclined or vertical; and if the
plant is growing vigorously they diverge so quickly that they become
almost horizontal in a day. But they move downwards in a rather oblique
line and continue for some time afterwards to move in the same
direction, in connection, we presume, with their spiral arrangement on
the stem. The course pursued by a young leaf whilst thus obliquely
descending was traced, and the line was distinctly yet not strongly
zigzag; the larger angles formed by the successive lines amounting only
to 135°, 154°, and 163°. The subsequent lateral movement (shown in Fig.
96, p. 231) was strongly zigzag with occasional circumnutations. The
divergence and sinking of the young leaves of this plant seem to be
very little affected by geotropism or heliotropism; for a plant, the
leaves of which were growing rather slowly (as ascertained by
measurement) was laid horizontally, and the opposite young leaves
diverged from one another symmetrically in the usual manner, without
any upturning in the direction of gravitation or towards the light.
The needle-like leaves of Pinus pinaster form a bundle whilst young;
afterwards they slowly diverge, so that those on the upright shoots
become horizontal. The movements of one such
young leaf was traced during 4½ days, and the tracing here given (Fig.
121) shows that it descended at first in a nearly straight line, but
afterwards zigzagged, making one or two little loops. The diverging and
descending movements of a rather older leaf were also traced (see
former Fig. 113, p. 251): it descended during the first day and night
in a somewhat zigzag line; it then circumnutated round a small space
and again descended. By this time the leaf had nearly assumed its final
position, and now plainly circumnutated. As in the case of the
Carnation, the leaves, whilst very young, do not seem to be much
affected by geotropism or heliotropism, for those on a young plant laid
horizontally, and those on another plant left upright, both kept in the
dark, continued to diverge in the usual manner without bending to
either side.
Fig. 121. Pinus pinaster: epinastic downward movement of a young leaf,
produced by a young plant in a pot, traced on a vertical glass under a
skylight, from 6.45 A.M. June 2nd to 10.40 P.M. 6th.
With Cobœa scandens, the young leaves, as they successively diverge
from the leading shoot which is bent to one side, rise up so as to
project vertically, and they retain this position for some time whilst
the tendril is revolving. The diverging and ascending movements of the
petiole of one such a leaf, were traced on a vertical glass under a
skylight; and the course pursued was in most parts nearly straight, but
there were two
well-marked zigzags (one of them forming an angle of 112°), and this
indicates circumnutation.
The still closed lobes of a young leaf of Dionaea projected at right
angles to the petiole, and were in the act of slowly rising. A glass
filament was attached to the under side of the midrib, and its
movements were traced on a vertical glass. It circumnutated once in the
evening, and on the next day rose, as already described (see Fig. 106,
p. 240), by a number of acutely zigzag lines, closely approaching in
character to ellipses. This movement no doubt was due to epinasty,
aided by apogeotropism, for the closed lobes of a very young leaf on a
plant which had been placed horizontally, moved into nearly the same
line with the petiole, as if the plant had stood upright; but at the
same time the lobes curved laterally upwards, and thus occupied an
unnatural position, obliquely to the plane of the foliaceous petiole.
As the hypocotyls and epicotyls of some plants protrude from the
seed-coats in an arched form, it is doubtful whether the arching of
these parts, which is invariably present when they break through the
ground, ought always to be attributed to epinasty; but when they are at
first straight and afterwards become arched, as often happens, the
arching is certainly due to epinasty. As long as the arch is surrounded
by compact earth it must retain its form; but as soon as it rises above
the surface, or even before this period if artificially freed from the
surrounding pressure, it begins to straighten itself, and this no doubt
is mainly due to hyponasty. The movement of the upper and lower half of
the arch, and of the crown, was occasionally traced; and the course was
more or less zigzag, showing modified circumnutation.
With not a few plants, especially climbers, the summit of the shoot is
hooked, so that the apex points vertically downwards. In seven genera
of twining plants[3] the hooking, or as it has been called by Sachs,
the nutation of the tip, is mainly due to an exaggerated form of
circumnutation. That is, the growth is so great along one side that it
bends the shoot completely over to the opposite side, thus forming a
hook; the longitudinal line or zone of growth then travels a little
laterally round the shoot, and the hook points in a slightly different
direction, and so onwards until the hook is completely reversed.
Ultimately it
comes back to the point whence it started. This was ascertained by
painting narrow lines with Indian ink along the convex surface of
several hooks, and the line was found slowly to become at first
lateral, then to appear along the concave surface, and ultimately back
again on the convex surface. In the case of Lonicera brachypoda the
hooked terminal part of the revolving shoot straightens itself
periodically, but is never reversed; that is, the periodically
increased growth of the concave side of the hook is sufficient only to
straighten it, and not to bend it over to the opposite side. The
hooking of the tip is of service to twining plants by aiding them to
catch hold of a support, and afterwards by enabling this part to
embrace the support much more closely than it could otherwise have done
at first, thus preventing it, as we often observed, from being blown
away by a strong wind. Whether the advantage thus gained by twining
plants accounts for their summits being so frequently hooked, we do not
know, as this structure is not very rare with plants which do not
climb, and with some climbers (for instance, Vitis, Ampelopsis, Cissus,
etc.) to whom it does not afford any assistance in climbing.
[3] ‘The Movements and Habits of Climbing Plants,’ 2nd edit. p. 13.
With respect to those cases in which the tip remains always bent or
hooked towards the same side, as in the genera just named, the most
obvious explanation is that the bending is due to continued growth in
excess along the convex side. Wiesner, however, maintains[4] that in
all cases the hooking of the tip is the result of its plasticity and
weight,—a conclusion which from what we have already seen with several
climbing plants is certainly erroneous. Nevertheless, we fully admit
that the weight of the part, as well as geotropism, etc., sometimes
come into play.
[4] ‘Sitzb. der k. Akad. der Wissensch.,’ Vienna, Jan. 1880, p. 16.
Ampelopsis tricuspidata.—This plant climbs by the aid of adhesive
tendrils, and the hooked tips of the shoots do not appear to be of any
service to it. The hooking depends chiefly, as far as we could
ascertain, on the tip being affected by epinasty and geotropism; the
lower and older parts continually straightening themselves through
hyponasty and apogeotropism. We believe that the weight of the apex is
an unimportant element, because on horizontal or inclined shoots the
hook is often extended horizontally or even faces upwards. Moreover
shoots frequently form loops instead of hooks; and in this case the
extreme part, instead of hanging vertically down as would follow if
weight was the efficient cause, extends horizontally or even points
upwards. A shoot, which terminated in a rather open hook, was fastened
in a highly inclined downward position, so that the concave side faced
upwards, and the result was that the apex at first curved upwards. This
apparently was due to epinasty and not to apogeotropism, for the apex,
soon after passing the perpendicular, curved so rapidly downwards that
we could not doubt that the movement was at least aided by geotropism.
In the course of a few hours the hook was thus converted into a loop
with the apex of the shoot pointing straight downwards. The longer axis
of the loop was at first horizontal, but afterwards became vertical.
During this same time the basal part of the hook (and subsequently of
the loop) curved itself slowly upwards; and this must have been wholly
due to apogeotropism in opposition to hyponasty. The loop was then
fastened upside down, so that its basal half would be simultaneously
acted on by hyponasty (if present) and by apogeotropism; and now it
curved itself so greatly upwards in the course of only 4 h. that there
could hardly be a doubt that both forces were acting
together. At the same time the loop became open and was thus
reconverted into a hook, and this apparently was effected by the
geotropic movement of the apex in opposition to epinasty. In the case
of Ampelopsis hederacea, weight plays, as far as we could judge, a more
important part in the hooking of the tip.
Fig. 122. Ampelopsis tricuspidata: hyponastic movement of hooked tip of
leading shoot, traced from 8.10 A.M. July 13th to 8 A.M. 15th. Apex of
shoot 5½ inches from the vertical glass. Plant illuminated through a
skylight. Temp. 17½°–19° C. Diagram reduced to one-third of original
scale.
Fig. 123. Smithia Pfundii: hyponastic movement of the curved summit of
a stem, whilst straightening itself, traced from 9 A.M. July 10th to 3
P.M. 13th. Apex 9½ inches from the vertical glass. Diagram reduced to
one-fifth of original scale. Plant illuminated through skylight; temp.
17½°–19° C.
In order to ascertain whether the shoots of A. tricuspidata in
straightening themselves under the combined action of hyponasty and
apogeotropism moved in a simple straight course, or whether they
circumnutated, glass filaments were fixed to the crowns of four hooked
tips standing in their natural position; and the movements of the
filaments were traced on a vertical glass. All four tracings resembled
each other in a general manner; but we will give only one (see Fig.
122, p. 273). The filament rose at first, which shows that the hook was
straightening itself; it then zigzagged, moving a little to the left
between 9.25 A.M. and 9 P.M. From this latter hour on the 13th to 10.50
A.M. on the following morning (14th) the hook continued to straighten
itself, and then zigzagged a short distance to the right. But from 1
P.M. to 10.40 P.M. on the 14th the movement
was reversed and the shoot became more hooked. During the night, after
10.40 P.M. to 8.15 A.M. on the 15th, the hook again opened or
straightened itself. By this time the glass filament had become so
highly inclined that its movements could no longer be traced with
accuracy; and by 1.30 P.M. on this same day, the crown of the former
arch or hook had become perfectly straight and vertical. There can
therefore be no doubt that the straightening of the hooked shoot of
this plant is effected by the circumnutation of the arched portion—that
is, by growth alternating between the upper and lower surface, but
preponderant on the lower surface, with some little lateral movement.
We were enabled to trace the movement of another straightening shoot
for a longer period (owing to its slower growth and to its having been
placed further from the vertical glass), namely, from the early morning
on July 13th to late in the evening of the 16th. During the whole
daytime of the 14th, the hook straightened itself very little, but
zigzagged and plainly circumnutated about nearly the same spot. By the
16th it had become nearly straight, and the tracing was no longer
accurate, yet it was manifest that there was still a considerable
amount of movement both up and down and laterally; for the crown whilst
continuing to straighten itself occasionally became for a short time
more curved, causing the filament to descend twice during the day.
Smithia Pfundii.—The stiff terminal shoots of this Leguminous
water-plant from Africa project so as to make a rectangle with the stem
below; but this occurs only when the plants are growing vigorously, for
when kept in a cool place, the summits of the stems become straight, as
they likewise did at the close of the growing season. The direction of
the rectangularly bent part is independent of the chief source of
light. But from observing the effects of placing plants in the dark, in
which case several shoots became in two or three days upright or nearly
upright, and when brought back into the light again became
rectangularly curved, we believe that the bending is in part due to
apheliotropism, apparently somewhat opposed by apogeotropism. On the
other hand, from observing the effects of tying a shoot downwards, so
that the rectangle faced upwards, we are led to believe that the
curvature is partly due to epinasty. As the rectangularly bent portion
of an upright stem grows older, the lower part straightens itself; and
this is effected through hyponasty. He who has read Sachs’ recent Essay
on the vertical
and inclined positions of the parts of plants[5] will see how difficult
a subject this is, and will feel no surprise at our expressing
ourselves doubtfully in this and other such cases.
[5] ‘Ueber Orthotrope und Plagiotrope Pflanzentheile;’ ‘Arbeiten des
Bot. Inst., in Würzburg,’ Heft ii. 1879, p. 226.
A plant, 20 inches in height, was secured to a stick close beneath the
curved summit, which formed rather less than a rectangle with the stem
below. The shoot pointed away from the observer; and a glass filament
pointing towards the vertical glass on which the tracing was made, was
fixed to the convex surface of the curved portion. Therefore the
descending lines in the figure represent the straightening of the
curved portion as it grew older. The tracing (Fig. 123, p. 274) was
begun at 9 A.M. on July 10th; the filament at first moved but little in
a zigzag line, but at 2 P.M. it began rising and continued to do so
till 9 P.M.; and this proves that the terminal portion was being more
bent downwards. After 9 P.M. on the 10th an opposite movement
commenced, and the curved portion began to straighten itself, and this
continued till 11.10 A.M. on the 12th, but was interrupted by some
small oscillations and zigzags, showing movement in different
directions. After 11.10 A.M. on the 12th this part of the stem, still
considerably curved, circumnutated in a conspicuous manner until nearly
3 P.M. on the 13th; but during all this time a downward movement of the
filament prevailed, caused by the continued straightening of the stem.
By the afternoon of the 13th, the summit, which had originally been
deflected more than a right angle from the perpendicular, had grown so
nearly straight that the tracing could no longer be continued on the
vertical glass. There can therefore be no doubt that the straightening
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.
To ascertain the nature of the movement of the sub-peduncle, whilst
bending downwards, a filament was fixed across the summit of the calyx
of a not fully expanded and almost upright flower, nearly in the centre
of the head. The main peduncle was secured to a stick close beneath the
head. In order to see the marks on the glass filament, a few flowers
had to be cut away on the lower side of the head. The flower under
observation at first diverged a little from its upright position, so as
to occupy the open space caused by the removal of the adjoining
flowers. This required two days, after which time a new tracing was
begun (Fig. 124). In A we see the complex circumnutating course pursued
from 11.30 A.M. Aug. 26th to 7 A.M. on the 30th. The pot was then moved
a very little to the right, and the tracing (B) was continued without
interruption from 7 A.M. Aug. 30th to after 6 P.M. Sept. 8th. It should
be observed that on most of these days, only a single dot was made each
morning at the same hour. Whenever the flower was observed carefully,
as on Aug. 30th and Sept. 5th and 6th, it was found to be
circumnutating over a small space. At last, on Sept. 7th, it began to
bend downwards, and continued to do so until after 6 P.M. on the 8th,
and indeed until the morning of the 9th, when its movements could no
longer be traced on the vertical glass. It was carefully observed
during the whole of the 8th, and by
10.30 P.M. it had descended to a point lower down by two-thirds of the
length of the figure as here given; but from want of space the tracing
has been copied in B, only to a little after 6 P.M. On the morning of
the 9th the flower was withered, and the sub-peduncle now stood at an
angle of 57° beneath the horizon. If the flower had been fertilised it
would have withered much sooner, and have moved much more quickly. We
thus see that the sub-peduncle oscillated up and down, or
circumnutated, during its whole downward epinastic course.
The sub-peduncles of the fertilised and withered flowers of Oxalis
carnosa likewise bend downwards through epinasty, as will be shown in a
future chapter; and their downward course is strongly zigzag,
indicating circumnutation.
The number of instances in which various organs move through epinasty
or hyponasty, often in combination with other forces, for the most
diversified purposes, seems to be inexhaustibly great; and from the
several cases which have been here given, we may safely infer that such
movements are due to modified circumnutation.