How Plants Think

The always-fascinating Oliver Sacks takes a break from his human patients to review several recent and old books on earthworms, jelly-fish, and plants in the NYRB. One is Daniel Chamovitz’s recent What A Plant Knows.

Sacks writes, “We all distinguish between plants and animals. We understand that plants, in general, are immobile, rooted in the ground; they spread their green leaves to the heavens and feed on sunlight and soil. We understand that animals, in contrast, are mobile, moving from place to place, foraging or hunting for food; they have easily recognized behaviors of various sorts. Plants and animals have evolved along two profoundly different paths (fungi have yet another), and they are wholly different in their forms and modes of life.”

Darwin argued that animals and plants are closer than we think and he was “was reinforced in this notion by the demonstration that insect-eating plants made use of electrical currents to move, just as animals did—that there was ‘plant electricity’ as well as ‘animal electricity.’ But ‘plant electricity’ moves slowly, roughly an inch a second, as one can see by watching the leaflets of the sensitive plant (Mimosa pudica) closing one by one along a leaf that is touched. ‘Animal electricity,’ conducted by nerves, moves roughly a thousand times faster. . . . Signaling between cells depends on electrochemical changes, the flow of electrically charged atoms (ions), in and out of cells via special, highly selective molecular pores or ‘channels.’ These ion flows cause electrical currents, impulses—action potentials—that are transmitted (directly or indirectly) from one cell to another, in both plants and animals.”

Along similar lines, Chamovitz argues that plants are capable of registering what we would call sights, sounds, tactile signals, and much more. Plants know what to do, and they ‘remember.’ But without neurons, plants do not learn in the same way that animals do; instead they rely on a vast arsenal of different chemicals and what Darwin termed ‘devices.’ The blueprints for these must all be encoded in the plant’s genome, and indeed plant genomes are often larger than our own.”