THE EVOLUTION OF THE MIND. 43 5
ficient unto itself. It is independent and free, but it is at the same time unspecialized and ineffective. Its career offers no scope for volition, for a single life unit can not control the elements which sur- round it. It is the sport of the wind and the wave. But the recog- nition of self and non-self, which in one form or another is the attri- bute of all life, is not wanting among the protozoa. Some of them develop this sense to a large degree. It is said that among the rhizopods are those whose appendages or pseudopodia are at once cast off if they come in contact with the appendages of another of the same species. This recognition of self and non-self is not intel- lect, but it is homologous with the impulses on which in the higher types personality depends.
All sensation has reference to action. If a creature is not to act, it can not feel. Wherever motion exists there is some sensitiveness to external conditions, and this is of the nature of mind. In a com- pound organism the nature and position of the sensorium or mind center depend on what it has to do, or rather on what were the duties the same structure had to perform in the life of the creature's ancestors.
A plant may be defined as a sessile animal. It is an organic colony of cells, with the power of motion but not that of locomotion. The plant draws its nourishment from inorganic Nature — from air and water. Its life is not conditioned on a search for food, or on the movement of the body as a whole.
The plant searches for food by a movement of the feeding parts alone. In the process of growth, as Darwin has shown, the tips of the branches and roots are in constant motion. This movement is in a spiral squirm. It is only an exaggeration of the same action in the tendrils of the growing vine. The course of the squirming rootlet may be deflected from a regular spiral by the presence of water. The moving branchlets will turn toward the sun. The region of sensation in the plant and the point of growth are identi- cal, because this is the only part that needs to move. The tender tip is the plant's brain. If locomotion were in question, the plant would need to be differently constructed. It would demand the mechanism of the animal. The nerve, brain, and muscle of the plant are all represented by the tender growing cells of the moving tips. The plant is touched by moisture or sunlight. It " thinks " of them, and in so doing the cells that are touched and " think " are turned toward the source of the stimulus. The function of the brain, therefore, in some sense exists in the tree, but there is no need in the tree for a specialized sensorium.
The many-celled animals, from the lowest to the highest, bear in their organization some relation to locomotion. The animal feeds