Do plants contemplate and act? A new study shows they do plan movements ahead of time. The authors show that climbing plants can perceive the thickness of the support and develop a plan to grasp the support. If the support is not thick enough it drops the plan.

Though plants cannot move from place to place they have been shown to exhibit a number of other subtle movements such as moving towards sunlight. Growing plants may also rotate around a central axis. This process is called circumnutation and was documented from the time of Charles Darwin.

In this study the authors asked two questions: Are climbing plants equipped with a form of perception that subtend anticipatory behavior? Are they able to plan and execute on the basis of stimulus perception?

In order to address the above questions they studied approach-to-grab behavior using two-digit appendage-like tendrils on a climbing plant. They used the plant Pisum sativusm, the garden pea.

To study the support grasping behavior the authors videorecorded the growth of the plants with and without support. When there was no stimulus (support) the plants turned towards the light and as there was no support to hold they fell to ground.

The two-digit tendril of the plant reaching the support.The node below the tendrils was equated "to an hypothetical wrist that accompanies the tendrils towards the support and the tips of the tendrils to an hypothetical thumb/index finger ensemble that during the approach phase assumes the coreography for grasping the support." Creative Commons. Scientific Reports volume 9, Article number: 16570 (2019).

In plants that had support, maximum tendril velocity was higher and tendrils reached out to the support as if they were perceiving it. The authors also showed that circumnutating tendrils are able to change direction when a support is present. When they presented the plants with the 2D-picture of the support, instead of a real support, the movement of the plant was similar to that observed when there was no support.

The authors speculate that the plants perceive the support by experiencing vision, using chemical clues or by using echolocation, or a combination of these signals. Apparently a plant could emit sonic clicks and capture the echo.

"We add to this observation suggesting that detection of unsuitable supports can occur well before any mechanical stimulation from impact, as our experiment with 2D photographs seem to demonstrate," authors state.