A Review of the Systems of Ethics Founded on the Theory of Evolution

by Cora May Williams

He also writes of the curvature of radicles which come in contact with obstacles at right angles:—

"The first and most obvious explanation of the curvature is that it results merely from the mechanical resistance to the growth in its original direction. Nevertheless, this explanation did not seem to us satisfactory. The radicles did not present the appearance of having been subjected to a sufficient pressure to account for their curvature. Sachs has shown that the growing part is more rigid than the part immediately above, which has ceased to grow, so that the latter might have been expected to yield and become curved as soon as the apex encountered an unyielding object; whereas it was the stiff, growing part which became curved. Moreover, an object which yields with the greatest ease will deflect a radicle: thus, as we have seen, when the apex of the radicle of the bean encountered the polished surface of extremely thin tin-foil on soft sand, no impression was left on it, yet the radicle became deflected at right angles. A second explanation occurred to us, namely, that even the gentlest pressure might check the growth of the apex, and in this case growth could continue only on one side, and thus the radicle would assume a rectangular form; but this view leaves wholly unexplained the curvature of the upper part, extending for a length of 8-10 mm.

"We were therefore led to suspect that the apex was sensitive to contact, and that the effect was transmitted from it to the upper part of the radicle, which was excited to bend away from the touching object. As a little loop of fine thread, hung on a tendril or on the petiole of a leaf-climbing plant, causes it to bend, we thought that any hard object affixed to the tip of a radicle, freely suspended and growing in damp air, might cause it to bend if it were sensitive, and yet would not offer any mechanical resistance to its growth.... Sachs discovered that the radicle a little above the apex is sensitive and bends like a tendril towards the touching object. But when one side of the apex is pressed by any object, the growing part bends away from the object."[119]

Acting on this idea, Darwin found, in many experiments, that the radicles of plants freely suspended in bottles, when brought into contact with the most yielding substances, bits of paper, etc., were deflected, in a very few hours, from their original course, and often at right angles to this. He says, further:—

"As the apex of a radicle in penetrating the ground must be pressed on all sides, we wished to learn whether it could distinguish between harder, or more resisting, and softer substances. A square of sanded paper almost as stiff as card, and a square of extremely thin paper (too thin for writing on) of exactly the same size (about one-twentieth of an inch), were fixed with shellac on opposite sides of the apices of twelve suspended radicles.... In eight out of the twelve cases, there could be no doubt that the radicle was deflected from the side to which the card-like paper was attached and towards the opposite side bearing the very thin paper.

"This occurred, in some instances, in nine hours, but in others not until twenty-four hours had elapsed. Moreover, some of the four failures can hardly be considered as really failures: thus, in one of them in which the radicle remained quite straight, the square of thin paper was found, when both were removed from the apex, to have been so thickly coated with shellac that it was almost as stiff as the card; in the second case, the radicle was bent upward into a semicircle, but the deflection was not directly from the side bearing the card, and this was explained by the two squares having become cemented laterally together, forming a sort of stiff gable from which the radicle was deflected; in the third case, the square of card had been fixed by mistake in front, and though there was deflection, this might have been due to Sachs's curvature; in the fourth case alone, no reason could be assigned why the radicle had not been at all deflected."

Darwin found, moreover, by experiment, that, when the tip of a radicle is burnt or cut, "it transmits an influence to the upper adjoining part, causing it to bend away from the affected side." This deflection resembles, in a very striking manner, the avoidance of sources of injury and pain on the part of animals.

And at the end of his book on the Movements of Plants, which contains very many other experiments bearing on the question of sensitivity in plants, the author writes, "It is hardly an exaggeration to say that the tip of the radicle thus endowed, and having the power of directing the movements of the adjoining parts, acts like the brain of one of the lower animals."

It is true that the plant does not react with the rapidity which characterizes the animal; Darwin found that radicles are not sensitive to temporary contact, but only to long, though to slight pressure. It is also true that the physical basis of the movement is more simple, and so more easily traceable in the plant than in the animal organism; yet why lay such especial stress upon this side of plant-life, since it is acknowledged that the physical basis is by no means peculiar to it, but that, on the contrary, all life-processes, in the animal as well as in the plant, have their physical side, although greater complexity of organization may make this more difficult to follow in the one case than in the other?

But we may begin at the other end of the scale and examine the facts presented from the opposite point of view. The physicist demonstrates that force is indestructible; that is, that the sum of the motion and resistance to motion residing in indestructible matter is also imperishable, that all present motion must be regarded as the resultant of previous conditions of motion and resistance, as far back as we may go, until we reach some assumed primal state (which is only assumed and cannot be proved to have existed) in which the matter composing the universe is supposed to have been at complete rest; and that every resultant bears relations to its component factors of force that are constant, every component finding its full value in the resultant. What evidence has the present state of our solar system and the other systems of heavenly bodies revealed to us by the telescope to offer us in proof of their consciousness or sentience? How are the whirl and concentration of nebular mists, the crash and collision of elemental bodies, from which, by simple action and reaction, after ages of disharmony, only a comparative harmony is arrived at as inevitable result, evidence of aim, intention, will, consciousness, in the matter subject to this evolution? Do we find anything here except blind law? The movements of plants, often directly favorable to self-preservation, may be explained by the arrangement of the cells and their chemical action. Or, if sentience must be assumed to be the cause of movement attaining ends of self-preservation in plants, how are we to account for organic and instinctive action in animals? How is it, for instance, that the new-born infant sucks, and the chicken but a few hours old, even though it has been hatched in an incubator apart from its kind, picks at the food strewn before it, aiming, too, with considerable precision?[120] How does it happen that the process of breathing and digestion, the beating of the heart and the circulation of the blood, all so necessary to life, go on with regularity, though not directed by reason? Has the newly hatched chicken any experience to teach it what food is, and how it is to be seized; or does the caterpillar, which spins itself a cocoon, do this with the understanding that it is about to enter a new phase of existence? Or, if such important and, at first view, seemingly intelligent action can be explained as unreasoning instinct, why cannot many other actions of the lower animals be thus explained? Why may not nearly all, if not all of them, be thus explained, and consciousness be regarded as the exclusive property of man?