REFLEXES, INSTINCT, AND REASON 449 



but slight degree. The discussion as to whether lower animals 

 have minds turns on the definition of mind, and our answer to 

 it depends on the definition we adopt. 



Most plants are sessile organisms. Each is an organic col- 

 ony of cells, with the power of motion in parts 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, nor on the movement of the body as a whole. 

 Yet the plant searches for food by a movement of the feed- 

 ing parts. In the process of growth, as Darwin has shown, 

 the tips of the branches and roots are in constant motion. This 

 movement is a spiral squirm. The movement of the tendrils 

 of the growing vine is only an exaggeration of the same action. 

 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 identical 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 si-nlight. It may be said, 

 in somewhat metaphorical language, that 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 on living creatures and these it must pursue if it 

 is to thrive. It is not the sensitive nerve tips which are to 

 move; it is the whole creature. By the division of labor the 

 whole body of the compound organism cannot be given over 

 to sensation. Hence the development of sense organs dif- 

 ferent in character: one stimulated by waves of light, another 

 by waves of sound; one sensitive to odor, another to taste; 

 still others to contact, temperature, muscular strain, and pain. 

 These sense organs must through their nerve fibers report to 

 a sensorium which is distinct from each of them. And in 

 the process of specialization the sensorium itself is subdi- 



