_The Cerebral Processes of Plants_
I find it good to think of plants as mysterious fellow-existences, about
which the half is not yet known--to speculate on their psychological
properties--on what has been called "The cerebral processes of plants."
Darwin has thus expressed himself on this interesting question:
"It has," he says, "always pleased me to exalt plants in the scale of
organized beings, and I therefore felt especial pleasure in showing how
many and what admirably well-adapted movements the tip of a root
possesses.... It was impossible in accordance with the principle of
evolution," he goes on to say, "to account for climbing plants having
been developed in so many widely different groups, unless all plants
possess some slight power of movement of an analogous kind. This I
proved to be the case."
In his "Power of Movement in Plants" he still farther expresses this
conviction: "The tips of all young growing parts of the higher plants
continually revolve, bowing successively towards every point of the
compass." And he declares that "it is hardly an exaggeration to say that
the tip of the radicle endowed with such diverse kinds of sensitiveness
and having the power to direct the movements of the adjoining parts,
acts like the brain of one of the lower animals, the brain being seated
within the anterior end of the body, receiving impressions from the
sense-organs and directing the several movements."
Great truths gain ground by inches. This assumption of the great
scientist is not yet generally admitted, although, as I think, well
established by experimental proof. An interesting paper in "Forest and
Garden," prepared by T. D. Ingersoll of Erie, Pennsylvania, and entitled
"Signs of Intelligence in a Madeira Vine."
I here copy verbatim:
"Two or three years ago I began, without any great seriousness, an
experiment on some Madeira Vines, which presently began to prove more
interesting than was anticipated. Before this my attention had been
attracted to peculiar movements made by this plant in the course of its
spiral ascent of a stick. If allowed to grow a few inches above the
support the extremity of the plant will sway backward and forward a few
hours and then will enter upon a regular revolving movement, always from
right to left, or contrary to the direction in which the hands of a
watch move. One revolution consumes about three hours. One of my plants
began to grow on April first, and at the end of fourteen days was twelve
inches tall and showing signs of uneasiness--now bending away from a
vertical position and again standing nearly upright. On the 16th it was
eighteen inches high, and, being too top-heavy to stand erect, it began
to fall away from the pot, which stood upon a table, towards the floor.
This was done gradually and apparently with conscious care. It seemed to
feel at times that it was letting itself down too fast, when it would
stop with a jerk, like a nodding child half asleep. When near the floor
it began describing ellipses, about three inches in diameter, with its
upturned extremity. On the 19th it was twenty-six inches in length, and
would describe a crescent-shaped loop, seventeen inches in length by six
inches in breadth, in about two hours. On the 23d it was three feet four
inches long, revolving with less regularity, and at times drooped as if
weary or discouraged in trying to find something upon which it might
entwine itself. Thus far no opportunity had been given the plant to
climb, since it was desirable to see what it would do to meet the
absence of some support. On the 26th a new route of traverse was
undertaken at 6 a.m., and at nine o'clock the extremity, which was near
the floor at the left side of the pot, had described a circle six inches
in diameter. It then slowly swept around to the right side and made
another irregular circle, and then returned to the left side of the pot;
these movements occupied just twelve hours. The track of the tip of the
vine was carefully traced with a pencil upon a sheet of paper laid
beneath it, and the entire line of traverse measured no less than six
feet nine inches. During the evening the plant became quiet, and
probably remained so all night. At 10 a.m. the next day, however, it
began pointing its tip in various directions, and at noon assumed the
form of a corkscrew, about four inches long, which posture it retained
until night and then straightened out. On May first the vine was lifted
and tied to a vertical support--a large thread--where it remained
entirely quiescent for two days. Then it began growing again as if it
had recovered from what had been for six days a condition near the point
of death.
"Another vine was observed carefully during several days of cloudy
weather. It uncoiled itself from the stick and reached away toward the
light at an angle with the horizon of forty-five degrees. It was
carefully recoiled about its stick, but after it had grown some three
inches more it unwound itself and stood away toward the window as
before. Time after time during the continuance of the cloudy weather it
was brought back to its support but invariably left it. Then followed a
fortnight of bright sunny weather, during which the vine showed no
disposition to escape from its stick or stop its twining growth.
Attempts were made to induce another plant to twine in the direction
opposite to its normal one, but no ingenuity could deceive the plant as
to its proper course. All the experiments seemed to show how much like
an animal was the plant in its sensitiveness, not only to changes of
light and temperature, but to harsh treatment. Whenever restrained or
forced, no matter how tenderly, out of its natural method of growth,
all progress was retarded and the health of the vine disturbed in a
marked degree. Plants seem to be creatures of feeling and the similarity
of movement and apparent purpose between them and the lower orders of
animals are used to strengthen their theory by those who hold to the
doctrine of the identity of life in the two kingdoms."
Dr. Dwight, in his paper in "Scribner's" entitled "Right-handedness"
still further develops the theory of brain power in plants. "The spiral
growth," says this writer, "of a graceful climbing plant, at first
sight, suggests nothing like right or left-handedness, but the analogy
when once seen is very striking. As the young plant begins its upward
course it is clear that to make the coils which it is its nature to
describe, it must either turn to the right or left. It might be supposed
that its deviation to either side is the result of an accident, but this
is impossible, for, though the individual plants of some kinds do twine
indiscriminately to either side, some only curl to the right and others
to the left. More remarkable still, some species twist in the opposite
direction to that of the larger families to which they belong, and
finally, sometimes a particular plant grows the wrong way. This is
analogous to being left-handed."
From Mrs. Pratt's "Flowering Plants of England" I take this account of
the curious movements of the seed-vessel of the "Musk Stork's Bill."
It is a relation of Mr. Mallet of Dublin of his personal observation of
the capsule movements of this remarkable flower. "Each seed," says the
writer, "of which there are five to each flower, is enclosed in a
carpel, attached by its upper extremity to a tail or awn, which
possesses the most wonderful hygrometric sensibility, as, indeed, does
every other part of the plant. These five awns lie in grooves in the
receptacle of the flowers, and this receptacle is central to and is the
axis of all parts of the flower and the fruit.
"When the whole system has arrived at a certain point of aridity the
awns, which are provided with an exquisite power of torsion, hoist
themselves out from their grooves and at the same moment a number of
downy filaments, hidden in the back or inward face of the awns, bristle
forth; they all now become detached and fall to the ground. But here
they still continue to twist, and from the position in which they always
lie keep tumbling over and over, and thus receding from the parent plant
until at length they become perfect balloons, ready to be wafted away by
every zephyr."
The theory that "plants can see," or, at any rate, manage to find food
and support by some special sense, which the unscientific mind cannot
better name than to call it sight, has been corroborated in the "Rural
Press" by Mrs. King, who thus describes her husband's observation of
this interesting habit on the part of a creeping plant in India:
"He was sitting on the veranda, with one foot up against a large pillar
near to which grows a kind of convolvulus. Its tendrils were leaning
over into the veranda, and, to Robert's surprise, he presently noticed
that they were visibly turning toward his leg. He remained in the same
position and in less than an hour the tendrils had laid themselves over
his leg.
"This was in the early morning, and when at breakfast he told me of this
discovery we determined to make further experiments. When we went out
into the veranda the tendrils had turned their heads back to the railing
in disgust. We got a pole and leaned it up against the pillar quite
twelve inches from the nearest sprays of convolvulus.
"In ten minutes they had begun to curve themselves in that direction and
acted exactly as you might fancy a very slow snake would do if he wished
to reach anything. The upper tendrils bent down, and the side ones
curved themselves until they touched the pole, and in a few hours were
twisted quite round it.
"It was on the side away from the light, and, excepting the faculty of
sight, we can think of no other means by which the tendrils could be
aware that the pole had been placed there. They had to turn away from
the light to reach it, and they set themselves in motion visibly within
a few minutes of the pole's being there."
My own experience with climbing plants has long since convinced me that
they have "a will of their own," and that if their will differs from my
own no amount of coaxing will induce them to take the path which is
laid out for them.
Well, if plants had but tongues they could, no doubt, tell us things
well worth hearing in regard to their special mode of existence.