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THE
NATIOxNALSECULARSOClETY
MOVEMENTS OF PLANTS.
By ERNEST A. PARKYN, M.A.
ROBABLY no phenomenon in Nature excites,
so much attention and enquiry as movement.
On perceiving the movement of any object,
we almost unconsciously look for its cause.
The movement of an apple falling to the
ground from an apple-tree is said to have
set the mind of Newton enquiring in a direction which
ultimately revealed the law of gravitation.
The soporific influence of custom and habit appears to
have had a less weakening effect upon the minds of men in
this direction than in most others. I mean that the neces
sary relation between cause and effect is more generally
admitted with regard to movement than other phenomena.
A person, for instance, who does not so much as ask for
the cause of any ordinary phenomenon, will often seek and
look for the cause of a movement coming under his
observation.
The cause to which the mind most readily refers move
ment is undoubtedly life. This is not to be wondered at,
for that which we most intimately associate with our own
vital activity are the movements of our bodies and of their
parts. Thus it is that the savage, when he first becomes
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The Movements of Plants,
aware that the stars move in the heavens, believes that
there is behind them a living cause; or when he first sees a
locomotive in action, believes it to be endowed with life.
But in thus referring movement to a living cause, that
cause is invariably associated with the animal world. Life,
as far as it is associated with obvious movement, is invari
ably referred to an animal, not to a vegetal source. The
very expression, “ vegetable life,” is synonymous with a
quiet, peaceful, motionless existence.
In fact, so deeply has this idea become ingrained in the
mind, that we have been religiously brought up in the
belief that one, perhaps the great distinction between
animals on the one hand and plants on the other is, that
whilst the former possess, the latter are wanting, in the
power of movement.
Unless there were a nucleus of truth in this idea, it
would doubtless not be so generally entertained as it is.
The extent of its truth depends upon what you mean by
the word movement, when applied to living things—to
animals and plants.
If by movement is meant locomotion, or movement from
place to place, and we restrict our observation to the
higher animals and plants, it is correct; but if, on the
other hand, we turn our attention to the lowest forms of
life, animal and plant, the distinction by no means holds,
for here we find that the lowest plants, like the lowest
animals, are endowed with the power of locomotion—they
are able to move from place to place, by exactly the same
means and in precisely the same manner, as do the lowest
animals. Moreover, some lowly animals are fixed and
incapable of moving from place to place. On the screen
you see illustrations of a few such lowly plants. Here, for
instance, is a lowly vegetal organism named Myxomycetes.
It is nothing more nor less than a mass of structureless
living matter, or protoplasm, which is capable of creeping
�The Movements of Plants.
3
about on any surface on which it may happen to rest.
There are certain lowly animals, which are well known in
the animal world, which are endowed with this curious
creeping movement, and here in this little plant we see
exactly the same kind of locomotion.
Here is a little plant which, under ordinary circum
stances, is green or red. It is a little spherical mass of
protoplasm, coloured green, and surrounded by a fine
membrane. At one spot you observe two fine filaments,
or cilia, which, by their active contraction, move the little
particle through the water. In the animal world there are
a great number of minute animals which are able to move
about in this manner.
If by movement, on the other hand, you mean not loco
motion, but movement of parts or members of an individual
organism, the distinction by no means holds, as I shall
endeavour to explain in this lecture. For recent observa
tions, more especially those of the illustrious Darwin,
have shown that all parts of plants—root, stem, leaf—
are in a state of continuous movement so long as they
are growing. As long as these parts of plants are
growing they are in a state of incessant movement;
in fact, the difference between the animal and the plant
would appear to be rather this, that whereas the
movements in the case of the former take place only now
and then—in other words, are intermittent—the move
ments of the parts of the latter take place continuously,
without intermission, so long as the parts are in a state of
growth.
Now, this movement which is observed in the different
parts of plants is of the nature of a nodding movement.
It is a movement from side to side, and it is therefore
usually spoken of by the word Nutation, from the Latin
nutatio, a nodding. Now, this nutation or nodding move
ment of plants is of two kinds—(1) simple, when the part
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The Movements of Plants.
moves from side to side, in one plane only ; or (2) revolving,
when it moves more or less in a circle. Revolving nuta
tion is also called circumnutation (Latin circum, around;
nutatio, a nodding).
In the first part of the lecture I want to endeavour to
explain the nature of this movement—its cause, and how,
by simple experiments, it has been shown to be exhibited
by the different parts of plants.
The next illustration on the screen will enable us to
appreciate this kind of movement better. Here is an
illustration of the simple nodding movement of the plant.
You are supposed to be looking down upon the stem in its
normal position, and you observe the marks supposed to be
made by the top of the stem as it sways to and fro in one
plane. That is simple nutation. But here is the revolving
movement illustrated. You again look down on to the top
of the stem, and see that it moves through each quarter of a
circle until it reaches again the point from which we started.
You notice that the side of the stem which faces the
centre of the circle described varies as the stem revolves.
After having moved through half-a-circle, the side which
first faced the centre now looks directly away from it, or
vice versd.
The cause of the movement is inequality of growth.
If one side of the stem grows more quickly than the other,
by simple mechanical principles the stem will bend over
on the side of lesser growth, and there is simple nuta
tion. If the inequality of growth travels gradually round
the stem, all portions of the stem will successively be forced
out of the perpendicular, or normal line, and revolving
nutation, or circumnutation, will be the result.
As to the means by which this movement is experimented
upon, you have here a flower-pot containing a growing
plant. A fine filament of glass, an inch or an inch and
a-half long, is taken, at one end of which is fixed a little
�The Movements of Plants.
5
round knob of sealing-wax. About two-thirds of the way
down a piece of paper is fixed, by the sharp end of the
glass being run through it. At one corner of the piece of
paper is put a black ink mark, and then the piece of glass—
which weighs very little indeed, being very fine—is fixed
at this end to the top of the stem. A large flat piece of
glass is then taken and placed above the stem at right
angles to it. Suppose, now, looking down through the
glass plate from above, you fix your eye on the knob of
sealing-wax at the end of the glass rod, and then move
your eye until the knob of sealing-wax directly covers the
black spot on the paper. When they are exactly in 'line,
you make a mark on the flat piece of glass above. Leave
the plant for an hour, and then go back and look at it in
the same way, and make another mark. This is repeated
again and again, until at last a considerable number of dots
have been made upon the glass plate. Now join these dots
together by lines, and you will find that the figure obtained
approaches more or less that of a circle.
The next illustration shows a few tracings taken in this
way. Here is the tracing obtained from a cabbage plant.
The arrows, showing the direction of the movement, travel
almost in the form of a circle. Of course I am not speaking
of a mathematically-correct circle. Here are also another
kind of cabbage and canary-grass, and here one of a cotton
plant. This is the way in which the observations are made
upon the stem.
The method adopted with the root is different, of course.
You cannot experiment with the root beneath the soil in
this manner. It is done in this way :—The tip of the root
is allowed to grow down upon a slightly inclined glass
plate, which has been blackened by being held over a smoky
flame, and upon which the slightest pressure will make a
mark. The end of the root is allowed to press against this
piece of glass, and as it grows down you find a mark on the
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The Movements of Plants.
sooty glass curving from side to side. This is seen in the
case of an oak plant on the screen. The marks in some
places are finer than in others, showing that the tip of the
root pressed more strongly sometimes against the glass than
at other times, pointing to its not having merely moved
from side to side, but to its moving more or less in a
circle.
The next illustration shows us a young seedling plant.
This is a pea. When you open a pea seed, you see
within it the young plant. You observe at the top a
little curved object; that is the very young stem. Then
you notice a little pointed shoot below; that is the young
root, or radicle. The mass of the seed is really made up of
two very big leaves. They are the leaves of the seedling
plant, and are therefore called the seed leaves. They
contain a great deal of nutriment, which is used up by the
young seedling when growing.
Here you have the seedling of the bean plant, which is
closely allied to the pea. It has come out from the seed, and
grown considerably : here you have the young stem, with
the first ordinary leaves upon it; this is the young root
growing down into the soil. I want you to notice that
coming off from the root are a number of fine filaments.
These are little hairs, and since they come off from the root
they are called root hairs. Now, the movement of the
root down through the soil is one which is worthy of a few
moments’ attention, inasmuch as the root is continuously
exhibiting this peculiar revolving movement, which helps it
to pass down through the soil. Of course when the root is
surrounded by hard soil it cannot move in this revolving
manner to any great extent. The nature of the soil prevents
it. But remember it is always trying to move. There
fore, if, for instance, a worm should pass along near
the root tip and push away the earth just by the root,
the root moves, taking advantage of the space that the
�The Movements of Plants.
7
worm has left, and so pushes down more easily into the soil
than it could when completely surrounded by it. In fact,
this revolving movement of the root enables it to move
down through the soil in the direction of least resistance.
Whenever the soil is removed it takes advantage of that in
virtue of being able to revolve. It is able in that way to
grow down where the soil offers the least resistance.
The movement of the root down through the soil is aided
in a much more wonderful way than that. I refer to the
help rendered by the root tip, which is sensitive to contact
and to moisture in a remarkable manner. Here you have
a young, a very young seedling of buckwheat; here is the
young stem with two leaves, and here you have the young
root. The end of the root, or root tip as it is called, is
extremely sensitive. When anything presses against the
tip it moves away from the object touching it. For
instance, supposing the root is growing down into the soil,
and comes against a hard object, such as a stone, so that the
tip presses on it, the root, instead of trying to push through
the stone, creeps away and goes down by the side of the stone.
It is worth while following the course of events here. What
happens ? You not only have the tip of the root moving,
which has been touched, but a part of the root above the
tip moves. The root moves completely away, so as to get
round the stone, instead of pushing against it, and so it
grows down into the soil, which it would not do if it were
to remain against the solid stone. The point is this, that
not only is the tip of the root sensitive to touch, just as
your fingers are, but it is able to transmit that “ touching ”
influence to a part of it above, and so cause the upper part
to move as well. The tip of the root is not only sensitive
to touch but to moisture. But the tip, instead of turning
away from moisture, turns towards it. Now that again, you
will see, is advantageous to the movement of the root down
through the soil. Suppose the root happens to come near
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The Movements of Plants,
to soil which is rather more moist than that above. It will
turn towards the moist earth, and, of course, it is easier to get
through moist earth than through dry earth. The resist
ance is less. Therefore the sensitiveness of the tip to moisture
which, instead of causing it to move away, causes it to move
towards it, is equally favourable to the movement of the root
down through the soil—in the direction of least resistance.
These little root hairs also play an important part in
enabling the root to penetrate through soil. The root hairs
are simply little tubes, each consisting of an external
membrane with living matter, or protoplasm, within. As
the root is passing down through the ground, the little root
hairs come into contact with the soil, and the remarkable
fact is this, that the membranes become partially liquified
at their extremities, so that minute stones, or particles of
earth, become mixed up with it. The membrane then
solidifies again, and in that way the end of the root hair
becomes quite fixed in that portion of the soil. This fixing
takes place in all directions. What is the result ? It is
this : that the root becomes fixed on all sides by the little
hairs, and so any force within the growing root which acts
in any direction must exert its influence in forcing the
root down through the soil. A force within the root may
tend to push it to the side or upwards, but it- cannot do so
when these little hairs are fixing it on all sides, and so any
force is exerted in pushing it down through the soil.
Let me conclude this portion of the subject with a
quotation from Darwin :—
“ If we look at a great acacia tree we may feel assured that
every one of the innumerable growing shoots is constantly
describing small ellipses, as is each petiole, subpetiole, and
leaflet. The flower stalks are likewise continually revolving.
If we had the power of a microscope, and could look beneath
the ground, we should see the tip of each rootlet endeav
ouring to sweep small circles as far as the surrounding
�The Movements of Plants.
9
earth permitted. All this astonishing amount of movement
has been going on year after year since the time when the
plant emerged from the soil as a seedling.”
Let me now refer briefly to the movement of the
stem. I wish to explain a remarkable resemblance between
the way in which the movement of the stem of plants is
influenced by light, and the way in which our own bodies
are influenced by the same agent. There is a striking
resemblance between the influence of light upon the move
ment of the stems of plants, and the influence of light upon
our own bodies—or that important portion of them which
we call the nervous system. The interest attaching to this
is due to the fact that nothing like a nervous system of
the animal body is known to exist within the bodies of
plants.
Now, there are no less than five different ways in which
this analogy can be shown to exist:—(1) The small amount
of light necessary to produce an effect; (2) transmitted
effects; (3) in exhibiting an after-effect; (4) the stronger
the stimulus the greater the effect; (5) the greater effect
produced after darkness than after exposure to light.
To begin with, everybody knows that the human eye,
which of course is part of our nervous system, is affected by
a very small amount of light. We can appreciate extremely
small quantities of light by our eyes. But, I think, even our
eyes are surpassed by the sensitiveness of plants to light.
I will just give one experiment. It has been known for a
long time, and you are probably well aware, that plants are
influenced by light in this way, that they turn towards the
source of light. Everybody knows that plants on the edge
of a forest will turn away from the inside of the forest, and
to the exterior, which is more brilliantly illuminated. That
is a fact that has been known for a very long time. The
first point is that plants seem extraordinarily sensitive to
light. ' A small seedling was placed in a pot, covered over
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The Movements of Plants.
with a tin vessel. In the tin vessel a tiny hole was made,
one-twentieth of an inch in diameter. The light could just
fall upon a certain portion of the seedling by means of this
microscopic hole. When, after a time, the tin vessel was
taken off, it was observed that the seedling had turned
most distinctly towards the little hole. That small amount
of light had affected the plant.
The next point is one which is analagous to the
transmission of effect. For instance : say the plant is above
the ground, and the stem is partially covered over, so
that only the upper part of it is exposed to the light. You
will find that not only will the upper and exposed part of
the stem turn towards the source of light, but that the
hidden portion will do the same. You can only explain
this by the fact that the light not only affects the top of the
stem, but transmits its effect to the lower part of the stem.
We can readily understand that in our own bodies. When
I look at a gas-light, I am aware of the fact. Why ? The
light acts upon my eye, but with that alone I should not
know that the gas-light was there. The eye transmits the
influence by means of nerves to the brain. There is a
transmission of the effect that affects my brain, and I am
able to see the light. Just in the same way, when the light
affects the top part of the stem, it is able to transmit
the influence of the light to its lower part, and cause that
also to move.
The influence of light upon plants exhibits what we
call an after-effect. You will have no difficulty in readily
understanding that. I shall speak first of the after
effect in the case of the human body. Suppose you wake
up on a fine sunny morning and look at the window. You
see a striking picture of the window—the light panes and
the dark sashes. You turn round, or without turning round
you shut your eyes, and you still see before you, when your
eyes are shut, the picture of the window; you see the
�The Movements of Plants.
II
bright panes and the dark sashes most distinctly. It is an
after-effect. The meaning of that is, that the influence of the
light upon the eye remains for a certain time after the source
of light is removed. You have exactly the same thing in the
case of the plants. Take a plant, for instance, and allow a
light to act upon it, so that it moves at a certain rate
towards the source of light; you then place the plant in
darkness. What do you observe ?—that the plant still
moves in the same direction as it did before. It is an
after-effect. The effect of the light does not stop directly
you take the light away, for the plant still moves on as it
did before. The light still exerts an influence—there is
an after-effect.
The rapidity of the movement of the plant towards the
light is proportionate to the intensity of light. It is quite
unnecessary to mention, with regard to the eye, that the
stronger the light acting upon the eye, the more we are
affected by it. That will be admitted at once. It is exactly
the same with the plant. If you allow a light of a certain
intensity to fall upon the plant, it will move towards the
light with a certain rapidity. If you then make another ex
periment, after carefully noting the rapidity with a stronger
light, it will move more quickly towards the source of light; if
you take stronger light still, it will move quicker still. You
are brought to the conclusion that the plant moves towards
the light in proportion to the intensity of the light.
Lastly, here is a most curious analogy between the animal
and the plant bodies, and that is in the greater influence
light has upon a plant after the plant has been in the dark.
When you came into this room it was illuminated, but you
did not experience anything unusual in your eyes. You were
not struck by any particular brilliancy. The lights are now
turned down for the lantern illustrations, but when they
are turned up again presently, you will be conscious of the
light acting upon your eyes, though it will not be any
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The Movements of Plants.
brighter than it was before. Your eye will be acted upon
more strongly by a light of the same intensity, because,
meanwhile, you have been in the dark. The same thing
occurs in the case of a plant. Take a plant and allow a
light to fall upon it for a certain time, and note the rate of
movement; then leave the plant in darkness for some
hours, and afterwards expose it to a light of the same
intensity as before. It will be acted upon more strongly
than before, and will move more actively towards the source
of light than it did before being in the dark. In these five
ways there is a very striking analogy between the effect of
light on the movement of plants and its effect on the
human body.
But this revolving movement of the plant is most strikshown in Climbing Plants. In fact, here it subserves
a very important use indeed. It is due to the power pos
sessed by certain portions of the climbing plants of moving
in a circle that they are able to climb as they do. There
are different kinds of climbing plants—hook-climbers, roof
climbers, twiners, tendril-climbers. The two last are the
most common, and of those only I shall speak to-night.
Everybody knows the nature of the hop or convolvulus
plants, which climb up poles or stems by twining round
them. On the screen we see this. Now, the way these
plants manage to climb is simple enough ; they possess this
power of revolving in a very marked degree indeed. In
fact, the last three or four, or sometimes five or six, joints
of the stem move in a circle. When one of these plants
comes first above the ground, of course there may be no
stick or anything round which it can climb. It will begin
to move, the uppermost joints sweeping small circles. It is
trying to find something round which it can twine. When
the hop-grower comes upon the scene, he sticks a pole into
the ground. It is put into the middle of the circle, as it
were, made by the revolving stem, and then the stem comes
�The Movements of Plants.
13
into contact with it, and of course twines around it. The
part which becomes pressed against the pole ceases to grow,
and becomes fixed against it. That portion which moves
round in a circle is the growing portion of the stem, and as
it grows it moves up the pole, for the circles will in
reality be parts of a spiral. This is very strikingly
shown in the “ Morning Glory ” on the screen. In a plant
(feropegia Gardnerix) observed by Darwin, the part of the
stem that revolved was no less than 32 inches long—nearly a
yard. In that way the diameter of the circle swept would
be something like two yards. The circle itself once estab
lished would be something like six yards, or nearly 18 feet.
Darwin took the plant into his study and placed it on the
table, and it continued to move—it moved at the rate of
half-an-inch a minute. Darwin says it was a most interest
ing spectacle to watch the long shoot sweeping this grand
circle continuously, night and day, in search of some object
round which it could twine.
The second class of plant comprises the tendril-climbers.
The Mexican Passion Flower in the screen is one of these.
A tendril is a very fine filamentous body, which does not
end in anything. It does not end in a flower or a leaf.
These tendrils have the power of revolving in a marked
degree. But over and above that, they are extremely sensi
tive. If you go into a hot-house and touch a tendril with a
stick, it will soon bend, and afterwards perhaps coil up. It
is sensitive to a touch. This is especially the case with the
termination—the end of it. When this end comes into
contact with a hard object, it is so sensitive, it gets hold of
it, and coils around it, and becomes firmly fixed to it. We
have here also a very striking example indeed of the trans
mission of effect. What we saw in the root and the stem,
we see in a most marked manner in the case of the tendril.
The effect produced on the end of the tendril by its sensi
tive nature is transmitted to the whole of the tendril, or
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The Movements of Plants.
nearly the whole of it, in such a way that it becomes coiled
in a beautifully spiral manner. This subserves two very
important purposes. By coiling in that way it simply
hauls up the stem of the plant, thus raising it to a
higher point. If you cut off the tendril, and pull out the
coil, it will be two or three times as long, and so you
see how considerably the coiling must pull up the stem.
But this coiling of the tendril also subserves another pur
pose. The spirally-coiled tendril acts very beautifully as
a spring. That is a useful purpose indeed, for a strong
wind would blow the plant out of its position. The tendrils
are extremely delicate, and the slightest strain would break
them. But the coil acts as a spring before the wind, and
the tendril is blown against without damage. It is stretched,
and when the wind has gone down, it resumes its proper
length. Here on the screen is a Vine and a Virginia
Creeper, which so easily grows up against the sides of walls
and houses. At the end of the tendril of the Virginia
Creeper are very curious little bodies that might be called
flat suckers. The end of the tendril becomes firmly fixed
and pasted against the wall by means of this little sucker
like body, and the plant is thus enabled to become fixed
against any perpendicular flat structure like a wall.
Sleep Movements.—These movements every child has
observed in certain flowers. The sleep of leaves is far
more common, however. Recent observation has shown
that an enormous number of leaves of different kinds of
plants exhibit this sleep movement. The peculiarity may
be briefly summarised by saying that the leaf at night puts
itself into such a position that the blade is perpendicular
to the zenith. The leaf, of course, in the day-time is
flattened out, exposing its upper surface to the sky. At
night it is at right angles with the sky, so that neither the
upper nor the lower surface is exposed to the sky. The
trefoil leaf of the clover may be instanced, which you see
�Ths Movements of Plants.
15
on the screen in both its normal and sleep position.
Here, too, is the Marsilea, a pretty water plant. This
Acacia which you now see is another. You may have
observed the Telegraph Plant in hot-houses; some of the
little leaflets of which the leaf is composed are continually
moving up and down—hence its name. At night the
leaves fall so as to be almost perpendicular, as is well
shown by the illustration on the screen.
As to the use of these sleep movements :—Their use
appears to be to protect the leaves from chills and frost at
night-time, by diminishing the loss of heat by radiation.
That plants do suffer from this cause is acknowledged by
the custom of protecting seedlings and fruit trees, by
covering them in cold weather. Direct experiments have
been made which point to this conclusion. The nature of
these experiments is this :—To compare the effect of cold
or even frost at night on leaves of two similar plants, one
of which is allowed to go to sleep in the normal manner :
the leaves of the other are prevented from sleeping by beingpinned out in their diurnal horizontal position. On the
leaves of the former very little dew is deposited, and they
are not much, if at all, injured by frost. On those of the
latter much dew is deposited, and great numbers of them
are blackened and killed by frost. Hence it is obvious
that the sleep movement is of a protective nature as far as
injury to the plant arises from loss of heat from the flat
surface of the blade of the leaf, or from loss of heat by
radiation.
Touch Movements.—In conclusion, I shall refer briefly to
another kind of movement, which is best known, and for
some reason is perhaps the most interesting, though not the
most common. These may be called touch movements. I
will take two examples :—The Sensitive Plant {Mimosa
pudica'); and the other, Venus’ Fly-trap {Dionoea muscipulaY The leaves of both these plants exhibit a very
�16
The Movements of Plants.
remarkable movement when they are touched. Here is
one leaf of the Sensitive Plant on the screen. If you touch
the last leaflet of this compound leaf—the leaflets of which,
being arranged like a feather, is sometimes called a
pinnate leaf—the leaflets all close up one after another, in
a very beautiful, regular movement. When this is finished,
the whole stalk of the leaf falls ; the leaf is then said to be in
the excited state, which is well seen in the illustration on
the screen. You have here one of the most striking examples
in the whole of plant life, as far as we know, of the transmis
sion of effect. When you excite the last leaf, you only touch
the very last leaflet; and what is the result ? You get the
movement of leaflets a long way off, and, further, you get
the movement of the whole stalk—simply as the result of
touching one tiny leaflet at the end. When I touch the
table I am aware of the fact, because the effect of the touch
is transmitted to the brain by means of nerves. We can
understand this in the case of the human body, where you
have a nervous system. But in plants, so far as we know,
we have no nervous system, and this phenomenon has
therefore much excited the attention of physiologists, and
they have been much puzzled to find a suitable or satisfac
tory explanation of what superficially appears so simple.
The proximate cause of the fall of the leaf is, however,
known, and this is what I want to endeavour to explain.
You notice that at the end of the stalk by which the leaf
is attached to the stem is a little oval enlargement. From
a fancied resemblance to a cushion, it is called the pulvinus
(Latin for cushion) of the leaf. This little pulvinus is
nothing more or less than a beautiful mechanical contriv
ance by which the leaf is enabled to fall down when the
end of it is excited. What happens, though we cannot
exactly explain how the excitement travels from the tennial leaflet to the pulvinus, is this:—When you take the
last leaflet between your finger and thumb, and stimulate
�The Movements of Plants.
17
it, the effect passes right along the leaf, until it reaches the
pulvinus. On arriving there it alters the constitution or
the mechanism of this curious cushion-like enlargement
in such a way as to cause the leaf to fall. A change takes
place within the cushion-like body, or pulvinus. On the
screen is a microscopic view of a pulvinus cut down through
the middle. In section it is circular. There is a woody mass
in the centre, around which are great numbers of what the
physiologist calls cells, containing living matter and water.
The walls of the cells in the upper half are thicker than those
forming the lower half. The real mechanism is composed of
the cells of the lower half, and what takes places is this:—
When you touch the end leaflet the effect is transmitted to
the pulvinus, and by some means, which we do not fully
understand, causes the cells in the lower half of the pul
vinus to discharge some of their contained water into the
spaces between the cells which previously contained only
air. As a result of this the little cells of the lower part,
instead of being distended, become flabby. The change
might be compared to a number of bladders passing from a
condition in which they are strongly distended by contained
liquid, to the slack state ensuing on the passage out of
some of the water. What is the result ? That the stalk
being no longer supported by the mass of distended cells
forming the lower half of the pulvinus, falls in virtue of its
weight.
A word or two regarding the Venus’ Fly-trap. This
plant is carnivorous—it is able to make use of insects as
food. Each leaf consists of two symmetrical halves. On the
upper surface of the leaf there are extremely sensitive
hairs—three little hairs on each half. If an unfortunate
insect touches a hair, it is caught in a trap; the two
valves very soon closing up, thus imprisoning the insect as
you see in the illustration on screen. The leaf gives out a
digestive liquid, and the insect is thereby made suitable for
�18
The Movements of' Plants.
absorption by the plant as its food. Now, in this case you
have a contractile organ of some kind by which the leaf,
on being excited, is moved so as to close up in the way I
have described.
In animals we have markedly contractile organs, or more
strictly speaking, tissue—viz., what we call muscle. The
evident existence of contractile tissue in animals and plants
has led to a close comparison of the two; and with very
remarkable results, to which, in conclusion, I will briefly
allude. It has been known for a good many years that the
muscular tissue of animals—the contractile tissue of
animals we call muscle—exhibits certain electrical pheno
mena—what physiologists call the muscle current.
Physiologists have proved that when these muscles undergo
contraction, the muscle current becomes diminished in
intensity—undergoes what is called a negative variation.
The enquiry was therefore made, “Does the contractile
tissue in plants exhibit similar electrical phenomena ? ”
Experiments on the Dionoea plant have shown that it
does. There is a leaf current just as there is a muscle
current, that when the leaf contracts by closing up, the
leaf currents also undergo a change, exactly similar to the
change which the muscle current undergoes when the
muscle contracts.
But that is not all. Suppose you take the muscle and
throw an electrical shock into it, causing it to contract;
the muscle does not contract directly you send the shock
into it. A very short time elapses first, as can be shown
by delicate physiological instruments. There is a sort of
hesitation period, as if the muscle were making up its
mind whether it should contract. It is in this period that
the change in the muscle currents, its negative variation,
takes place. When you make an experiment with the
Venus’ Ely-trap, you also find this hesitation period. A
certain period elapses between the moment when you
�The Movements of Plants.
19
stimulate the leaf and the moment when it closes up.
Further, the change or negative variation in the leaf
current in the plant also takes place in this period. The
analogy, therefore, between the contractile tissue of the
animal or muscle, and the contractile tissue of the plant,
as exhibited in the Dionoea, is as complete in every
particular.
There is one more fact that is more striking still to my
mind. It has been shown that these hairs are sensitive
only to touch. They must be touched by something. The
most interesting point is this : they are most sensitive of all
to a human touch. Professor Burdon Sanderson, on whose
authority I make this interesting statement, could come to
no other conclusion than that the stimulus which causes
the leaf most readily and actively to contract is a human
touch.
What is a human touch ? A human touch is the
result of a combined contraction of a great number of
muscles, of the contractile animal tissue ; and his observa
tion tells us this—that that which most readily causes the
contractile tissue of this plant to be thrown into activity
is a stimulus resulting from the activity of the contractile
tissue—the muscle of an animal. One might almost say
that in this case there is some magnetic sympathy between
the contractile tissue of the animal and the contractile
tissue of the plant.
It would be very unbecoming in me if I concluded this
lecture to-night without referring to the illustrious man of
science to whom we are so much indebted for so many
of the observations and results which I have briefly brought
before your notice to-night,—observations which, apart
from their inherent interest, have a charm of their own, in
asmuch as they formed almost the concluding and crowning
work in the most laborious life of the greatest of modern
naturalists : the work of one whose marvellous powers of
�20
The Movements of Plants.
observation, whose unrivalled genius for the interpretation
of nature, whose devotion to the scientific spirit, whose
fidelity to truth, calmness of judgment, and fairness in
controversy, should make him the master of every student,
of every lover of nature—Charles Darwin.
Printed by Walter Scott, Felling, Nerocastle-on-Tyne.
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Victorian Blogging
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A collection of digitised nineteenth-century pamphlets from Conway Hall Library & Archives. This includes the Conway Tracts, Moncure Conway's personal pamphlet library; the Morris Tracts, donated to the library by Miss Morris in 1904; the National Secular Society's pamphlet library and others. The Conway Tracts were bound with additional ephemera, such as lecture programmes and handwritten notes.<br /><br />Please note that these digitised pamphlets have been edited to maximise the accuracy of the OCR, ensuring they are text searchable. If you would like to view un-edited, full-colour versions of any of our pamphlets, please email librarian@conwayhall.org.uk.<br /><br /><span><img src="http://www.heritagefund.org.uk/sites/default/files/media/attachments/TNLHLF_Colour_Logo_English_RGB_0_0.jpg" width="238" height="91" alt="TNLHLF_Colour_Logo_English_RGB_0_0.jpg" /></span>
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Conway Hall Library & Archives
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Conway Hall Ethical Society
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Title
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The movements of plants
Creator
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Parkyn, Ernest Albert, 1857-
Description
An account of the resource
Place of publication: [London]
Collation: 20, [3] p. ; 18 cm.
Notes: Lecture delivered before the Sunday Lecture Society, 28 Feb. 1886. Publisher's advertisements on unnumbered pages at the end. Lacks imprint: supplied from OCLC WorldCat. Part of the NSS pamphlet collection.
Publisher
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[Sunday Lecture Society]
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[1886]
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N535
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Nature
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<a href="http://creativecommons.org/publicdomain/mark/1.0/"><img src="http://i.creativecommons.org/p/mark/1.0/88x31.png" alt="Public Domain Mark" /></a><span> </span><br /><span>This work (The movements of plants), identified by </span><a href="https://conwayhallcollections.omeka.net/items/show/www.conwayhall.org.uk"><span>Humanist Library and Archives</span></a><span>, is free of known copyright restrictions.</span>
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application/pdf
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Text
Language
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English
NSS
Plant Physiology