Pavlov’s Peas

In the 1890s, Ivan Pavlov learned that he could condition dogs to salivate in anticipation of food whenever he rang a bell. To accomplish this, every time he fed the dog, he would ring a bell first. Eventually, the dog began to anticipate food whenever it heard the bell, even when the scientist stopped feeding the dog right after the bell. This is classical conditioning.

Now, marine animal ecologist Monica Gagliano has decided to try the experiment with living things that don’t have brains. Perhaps possessed by the ghost of Mendel, she has chosen the pea plant. Her book, Thus Spoke the Plant: A Remarkable Journey of Groundbreaking Scientific Discoveries and Personal Encounters with Plants, is a collection of first-hand accounts from her research into plant communication and cognition. She investigates behavior and perception of plants, testing their ability to hear sound, sense magnetism, and more. Let’s look at her pea conditioning experiment:

First she chose her bell: a fan that blows air on the pea plant. Running a control, she tested to make sure that the fan alone had no effect on the plant. Then she put the plant in a maze so that it would be easy to record which way the plant has decided to grow. Then she began to condition the plant in the way that Pavlov conditioned his dog. She blew the fan on the plant and then shined some blue light (aka plant food) from one direction. Naturally, the plant chose to grow in the direction of the light. You see this when you put a plant in the window: it grows toward the sun. But then, after much conditioning, she took the light away and only used the fan. The pea plant still decided to grow in the direction where it anticipated the light would be!

Plants have no brain in the conventional sense nor nervous system. Are brains and neurons really the essential ingredient for this behavior? Can you think without a brain? Leave your thoughts in comments.