Dear Ella,

I love plants. But when I hug a tree, does it love me back? Does it think about anything at all?

I talked about your question with my friend Michael Knoblauch. He’s a plant scientist at Washington State University.

He told me that whether or not plants have feelings or conscious thought is an open question. Right now, most scientists think it’s unlikely.

Animals like us feel and think—and we’re aware that we feel and think. Scientists believe that has to do with how our brains evolved.

Plants don’t have brains and nervous systems like ours. They can send and receive signals, but that seems to be automatic.

“They clearly show reactions,” Knoblauch said. “But they’re not conscious reactions. The plant always does the same thing or makes the same chemical. It doesn’t say, ‘Oh, today I’m too tired for it. I’m not going to make the chemical.’”

This is how scientists like Knoblauch see plants sending signals. In this microscope video, a scientist touches one plant cell with a glass rod. You can see a wave when the touch happens (1:33) and a faster wave when they stop touching the plant cell (6:45). Video: Washington State University, ©Nature Plants

Think about how plants respond to predators. When a hungry rabbit nibbles a leaf, the plant can’t pull up its roots and run away. It can’t ball up its leaves and punch the bunny.

Instead, most plants make defensive chemicals. The chemicals make the plant taste bad or harder to digest.

A plant with strong defenses will sense damage to its leaf and send signals to its other leaves. The signals tell the leaves to release the chemicals and hopefully send the rabbit hopping.

As far as we know, a leaf never gets that signal and ignores it because it thinks the rabbit is cute.

Sometimes plants send chemical signals in the air or soil. Scientists call these volatile compounds. Other plants and animals respond to those signals, too.

Have you ever smelled freshly cut grass? That scent is a volatile compound that grass plants release when they’re damaged.

The grass doesn’t know if the damage comes from a mower or a very hungry caterpillar. It just automatically sends the signal.

Sometimes other plants pick up the message. They start signaling so their own chemical defenses are ready. Sometimes insect predators pick up the message. They zoom over to see if there are tasty caterpillars doing the damage.

It’s tempting to imagine that means plants and insects talk and help each other like we do. But it’s more like how the cells in our bodies send signals. Sometimes we describe those signals as chemical messages, too.

When you woke up, a chemical message signaled your body to feel hungry. Later, another one signaled you to feel full. That automatically happens. You might make the conscious decision to ignore the message and skip breakfast. But your cells don’t ever decide to sleep in and not send signals.

We can’t ask plants about their internal experiences to see if they make decisions. Scientists rely on evidence they can test.

“If you do an experiment a hundred times under precisely the same conditions and get the same reply a hundred times, it’s probably not a conscious decision,” Knoblauch said. “If you got different replies, though, that’s likely a conscious decision.”

Fortunately, plants don’t need to think about how much they love my hugs for me to enjoy hugging them. We’re both living things adapting to the environment, and you better be-leaf I’m rooting for them.

Sincerely,

Dr. Universe