stimuli, which are carried to the contractile elements by nervous
threads, the internal energy representing the external stimulus being
called nervous energy or neurism. But where a nervous system does not
exist, as is the case in some low animals and in all plants, external
stimuli must be justly supposed to be converted into the same form of
energy, which in such organisms has a general circulation throughout
the contractile protoplasm. The attainment of some position, favorable
for the procurement of relief from some unpleasant sensation, or the
acquisition of some agreeable one, or for both, is the important thing
directly subserved by such movements in the generality of animals.
While we have the best of reasons for believing this to be true in
the vast majority of animals, because fundamentally their structure
is similar to our own, yet the inference that the same is true of the
lowest forms of life is justifiable until it is proved to be mistaken.
Whatever be the nature of any movement, whether the projecting of
portions of its own body-substance as pseudopodia in the primitive
animal, the movement of flagella or cilia in more specialized forms,
or the turning of the radicle of a plant-seedling in overcoming some
obstacle, there is no resisting the conclusion that the functions of
these organs, when once called into existence, are due to stimuli
not unlike those which affect the motions of the limbs of the higher
animals, and that the preliminary to all such movements, which are
not automatic, is an effort. And as no adaptive movement is automatic
the first time it is performed, effort, therefore, may be regarded
as the immediate source of all movement. Now, effort is a conscious
state, and implies a sense of resistance to be overcome. But when an
act is performed without effort, resistance has been overcome, and the
mechanism requisite for its performance has been completed. Automatism
has now been reached. New movements, in their incipiency, necessarily
meet with resistance. How this resistance is overcome, there seems to
be some diversity of opinion among physiologists and metaphysicians,
but it is generally believed that some such mental state as a sensation
or a desire, which may or may not stimulate a natural process as an
intervening element in the circuit, is concerned in its subduement.
That sense-perceptions are stimuli to the immediate appearance
of structural changes or movements is shown by the production of
color-changes in animals through changes in the condition of the organs
of sight and in the bending of the radicle of a seedling-plant a short
distance above its tip in obedience to a communication from the tip of
a sensation of hardness, caused by contact with a stone experienced in
its downward progress in the ground.
[Illustration: TIP OF RADICLE OF SEEDLING MAPLE.
Lower Cells Show Where Consciousness is Supposed to Reside.]
New conditions bring forth new acts in animals. No one can deny this
statement, as instances of its truth are too frequent to believe
otherwise. That such may be predicated of plants, which have not the
ability, as a rule, to meet with new conditions by reason of their
being affixed to the soil, very few persons are willing to admit;
but there is no getting away from the fact. The tip of the radicle of
a plant not only has the power, acting as a brain, as it would seem,
of guiding the root out of the reach of an obstacle that would be
injurious, or in the direction of water when it would be an advantage,
but a tendril has also the ability, in obedience to some inherent
force, of making its way to a support that has been purposely placed
in the near distance for its especial benefit. No external agencies,
which the materialistic naturalist has devised for accounting for the
movements of plants and low types of animal existences that are devoid
of a visible nervous system, can possibly explain these movements,
which are only explicable on the theory that nervous energy may be
elaborated and be distributed without such a system by and through the
general mass of the plant or animal, or by and through such parts as
may be necessary to its good.
No one who has experimented with the Droseras or Sundews, can have
failed to observe the extreme sensitiveness which resides in their
leaves. That these plants manifest a comparatively high order of
consciousness, there can be no question. Try them with insects, or rare
bits of meat, as articles of diet, and in a few hours, if vigorous
leaves have been experimented with, the leaves will have folded around
the food and commenced their curious process of assimilation. Mineral
substances, such as bits of chalk, magnesia and small pebbles, have no
such effect. They seem to ignore these things, just as an intelligent
animal would if they were placed by its side. Some experiments made
by Mrs. Treat, several summers ago, go far to confirm the statement
that plants are endowed with some sort of consciousness. _Drosera
filiformis_ was the species used in her experiments. Some living flies
were pinned one-half an inch from the leaves, but near their apical
extremities. In forty minutes the leaves had perceptibly bent toward
the flies, and in little more than an hour had reached the prey, the
legs of the latter being entangled and held fast by the tentacles of
the leaves. Next, the flies were removed three-quarters of an inch
further from the leaves, but the latter, even though bent away from
the direction of the light, failed to reach them at this distance.
What was it that induced the leaves to stretch in the direction of the
flies? Had the sun been shining from that side, it might be said that
the movement of the leaves was influenced by its light and heat, for
plants as a general rule turn toward that part of the heavens where
these energies are the most effective. It cannot be that they were
produced by some emanation of moisture from the bodies of the flies,
or by any influence that might be exercised by the vibratory movements
of their wings. No vain imaginings of such character will suffice for
their explanation. The energy necessary to explain this phenomenon
must come from within the leaves themselves. There was felt within
them a desire for food, and it was this desire that led the leaves to
bend away from the light and in the direction of the objects whose
presence created in them that sensation. But how they were able, in the
absence of any visible sense-organs, to determine the presence of these
objects, is difficult to surmise. That they are sensitive to contact is
generally conceded. And in them, no doubt, the sense of touch is keenly
developed. Granting this to be the truth, then they see, as a blind
man sees, by the sense of feeling. Currents of air, established by the
vibration of the insect’s wings, impinging upon the epidermis of the
leaves, affect the cells beneath, and a nervous influence is started,
guided by some central agency, of which we know nothing, causing the
leaves to bend in the proper direction. But why the leaves do not
thus bend when impinged upon by currents other than those produced
by insects, I am unable to say. Even as a blind man, though deaf, is
able through the sense of touch to discriminate moving objects by the
currents of air they excite, so it may be presumed that the leaves of
Drosera are endowed with the same wonderful and intelligent capacity.
Such a feeling once experienced would be apt to be known again, for
it would become fixed in consciousness by a process of memory. That
Drosera, whose habits are more animal-like than plant-like, must occupy
a high position in the scale of vegetable life, there can be no reason
to doubt from what has been said, and this assumption receives a most
remarkable confirmation from the fact that there are evidences, not
apparent however, of a sort of nervous system in its make-up, as shown
by the discovery of Darwin that by pricking a certain point in a leaf
one-half of its substance becomes paralyzed.
Wonderful as these facts are, yet they are not more so than some
recent discoveries made by Stahl while studying the simple movements
and physical conditions of certain low plants called Myxomycetes. In
their young stages these plants wander from the parts of the deposit
on which they are creeping, and which are gradually drying up, toward
those which are more moist. It is possible, by bringing moist bodies
in proximity to any ramifications, to produce pseudopodia, which lift
themselves from the deposit, and soon come into contact with the moist
object, so as to enable the whole mass of the plasmodium, that is, the
large, motile, membranous protoplasmic body formed by the coalescence
of the swarm-spores of the Myxomycetes, to migrate thereon. But on
the entrance of the plasmodia into the fructifying condition, the
Myxomycete quits the moist deposit, technically called the substratum,
and creeps upwards on to the surface of dry objects. Unequal
distribution of warmth in the substratum and unequal supplies of oxygen
and chemical substances soluble in water also cause locomotion in these
strange organisms. Let the plasmodia come into contact on one side
with solutions of saltpetre, carbonate of potash or common salt, and
they at once withdraw from the dangerous spot; but an infusion of tan,
or a dilute solution of sugar, causes a flow of the protoplasm and an
ultimate translocation of the entire plasmodial mass towards the source
of nourishment. Some solutions have an attractive or repulsive effect,
but this is in accordance with the degree of their concentration.
Unlike what is so natural to plants in general, the Myxomycetes seem to
have an aversion to light, as shown by their disposition to withdraw
from its presence.
How such tender structures as the Myxomycetes, which are destitute
of every kind of external protection, are enabled to carry on their
existence, the knowledge of the remarkably delicate reaction of
their plasmodia under external influences prepares us to understand.
Plasmodia, which are not yet ripe for reproduction, are kept in the
moist substratum by their peculiar affection for moisture and utter
dislike of the light. But within the darkness and moisture of the
substratum the plasmodia do not necessarily remain in one place,
for the differences in the chemical composition of the substratum
cause continual migrations. Nothing more remarkable can be said of
the plasmodia than that they have a wonderful faculty of avoiding
harmful substances, and, traversing the substratum in all directions,
of taking up the materials they require for food and growth. When,
however, their internal changes have advanced so far that the plasmodia
are approaching the fructifying condition, they are brought by their
dislike for moisture, which now sets in, from the moist ground of
forest or wood which they affect to the surface, where they creep up
various upright objects, frequently not doing more than forming rigid
reproductive capsules at some height from the ground. If, however, the
substratum becomes gradually colder, as is the case in autumn, a change
which sets in at the surface moving downwards, then the plasmodia
migrate into deeper regions still having a higher temperature; but when
the cooling proceeds very gradually, which especially happens in large
tan-heaps, the plasmodia may in their migration attain considerable
depths, where they then change into sclerotia, which are hard tuberous
substances, resembling the tubers and bulbs of flowering plants.
If, however, the temperature begins to ascend, the sclerotia again
germinate, and movement takes place from the deeper and cooler parts
to the upper already named.
Thus we see, in the locomotion of the Myxomycetes, extremely
interesting cases of movements due to stimulation. Light, heat,
moisture and gravitation are, in general, stimulus-movements, and
ultimately all growth depends on stimulus-movement, the most primitive
kind of protoplasmic movement. No causes other than those which
actuate higher organisms can be discerned to account for this lowest
type of organic movement. What form of inorganic energy can be cited
of sufficient potency to cause the organism to change, and without
regard to gravitation or any known form of attraction or repulsion,
its position in obedience to stimuli acting for its self-preservation?
There is none. In the Fuligo, or Tan Flower, a most remarkable example
of designed movement has been observed. This form will, according
to H. J. Carter, in its early amœbula stage, when isolated from the
sawdust and chips of wood among which it has been living, adapt itself
to the water of a watch-glass, or any other shallow vessel, in which
it may happen to be placed. But, if the watch-glass be placed upon the
sawdust, then it will make its way over the side of the glass to get to
the sawdust. Here is probably shown a sense-perception of the presence
and position of the tan-bark, as well as a feeling of desire to go to
it. May not this desire have been due to a sense of discomfort induced
by the surrounding water, or to the calling up in memory of some
superior comfort associated with the tan-bark?
Man in his self-complacency thinks that he knows the plants about
him. It is true that he has noted their form, their anatomy, their
color and their resemblances and differences, but how few have studied
them in meadow and woods by the light of a lantern at night or by
the silver rays of the moon. One feels on such an occasion as though
he had stepped from his threshold upon a foreign soil. Folded leaves
and strange sleeping forms will be found to confront you in every
direction. Of the nature of the nocturnal movements of plants, as well
as their varied and curious attitudes, both in leaves and flowers,
much speculation has been rife among botanists. In many flowers the
night attitudes have been conclusively shown to have relation solely
to their fertilization by insects; but the drooping night attitudes
of the leaves were supposed to indicate an aversion to moisture, many
plants seemingly verifying the conjecture by the assumption of the
same position during rain as in the dew. But when the same pranks were
played on a cloudy day or a dewless night, the explanation had to be
abandoned. With the clovers, the nocturnal positions of the heads seem
to be assumed only in the darkness, and this invariably, dew or no dew,
while the leaves appear to revel in the rain, remaining freely open,
their chief concern being the protection of the young blossom-clusters.
Were our eyes sharp enough we might discern a certain strangeness
in the nocturnal expression of every plant and tree. But in no tree
is this expression so remarkably emphasized as in the locust, a
member of the same leguminous order of plants with the clover. These
trees are especially noted for the pronounced irritability of their
leaves, and odd nocturnal capers, whose seeming vital consciousness
has induced some authorities to place them at the extremity of their
system, in contact with the limits of the animal kingdom. How strange
the pigweeds look at night! Their upper leaves, which during the day
had extended wide on their long stems, now incline upward against the
stalk, enclosing the tops of the younger branches, but still older
plants are seen with leaves extended much as at mid-day, but nearly all
turned edgewise by a twist in the stem. Circling in a close curve, the
creeping-mallow blossom now ignores her proud array of cheeses, and
the oxalis flower has forgotten her shooting pods to keep the vigil,
closed and nodding upon her stem, while her leaves masquerade in one
of the oddest disguises, their three heart-shaped leaflets being seen
reflexed and adjusting themselves back to back around the stem with
many contortions. Whatever the function of this strange nocturnal
movement may be, and it is still a matter of dispute with botanists,
one thing we are certain about, that is, its essential condition to the
life of the plant, careful experiment having demonstrated, according
to one authority, that “if the leaves are prevented from so regulating
their surface, they lose their color and die in a few days”--a fact
which Darwin has just as conclusively shown to be the case with other
plants.
Flowers that bloom by night could hardly be suspected of that vanity
which Rhodora has been made to confess by Emerson in his beautiful
lines to this flower. Our evening primrose does not bloom in the
dark hours for mere sentiment or moonshine, but from a nature which
lies, figuratively speaking, much nearer her heart. “Often when the
nights are very dark,” says an old writer, “her petals emit a mild
phosphorescent light, and look as if illuminated for a holiday. And
he who does not fear to be out in her mild and lovely haunt may see a
variety of nocturnal ephemeræ hovering around the lighted petals, or
sipping at the flowery fountains, while others rest among the branches
or hurry up the stems as if fearing to be too late.” From the first
moment of her wooing welcome it would seem that our evening primrose
listens for murmuring wings, and awaits that supreme fulfilment
with joyous expectancy, for it will invariably be found that these
blossoms, which open in the twilight, have adapted themselves to
crepuscular moths and other nocturnal insects, a fact which finds a
striking illustration in the instances of very long tubular-shaped
night-blooming flowers, like the honeysuckle and divers orchids, whose
nectar is beyond the ability of any insect but a night-flying hawk-moth
to attain. True, it is, that in other less deep nocturnal flowers the
sweets could be reached by butterflies or bees if the blossoms were
left open. But the night-murmurers receive the first invitation, which,
if accepted, leaves but a wilted, half-hearted blossom to welcome the
sipper of the sunshine. This beautiful expectancy, somehow or other,
determines the limit of its bloom. However, in the event of rain or
other causes preventive of insect visits, the evening primrose will
remain open for the attention of the butterflies during the ensuing
day, when otherwise it would have perceptibly drooped, and extended
to them but a listless welcome. Most strikingly may this fact be seen
illustrated in a spray of mountain-laurel. For nearly a week have I
observed in my house these blossoms lingering in patient expectancy,
when the flowers on the parent shrub in the woods had fallen several
days before, their mission in life having been fulfilled. In the house
specimens the radiating stamens, which are naturally dependent upon
insects for their release, and the consequent discharge of the pollen,
remained in their pockets on the side of the blossom-cup, a support,
as it seemed, for the bracing up of the corolla upon its receptacle.
But when the operation of releasing the stamens was artificially
consummated, the flower-cup soon dropped off or withered upon the
peduncle.
Not mainly has the writer, in attributing a phosphorescent quality
to the evening primrose, followed the license of fancy, for, if
scientists are to be believed, the regular luminous glow of this
and other nocturnal flowers has long attracted the attention of the
curious, and positive qualities of inherent light have been accorded
in many instances. It is true, as one authority asserts, that “the
evening primrose is perfectly visible in the darkest night,” from
which fact phosphorescent properties have been ascribed to it. Many
well-authenticated cases are on record of luminous, electrical,
lightning-like phosphorescence playing about flowers, the daughter
of Linnæus having been the first one to note such an interesting
phenomenon. Similar flashes or corona have been observed in
nasturtiums, double marigold, geraniums, red poppy, tuberose, sunflower
and evening primrose. According to various authorities, and it would be
a rash and presumptuous commentator who would dare to challenge such
an array of competence, many beautiful surprises await the traveller
among the dewy shadows. Whoever has made such a journey will not only
return with the consciousness that he has doubled his possessions, but
that he has also explored a new world--a realm which he can look in
the face on the morrow with an exchange of recognition that was truly
impossible yesterday.