(Re)claiming plants in comparative psychology.

Abstract

Up until the middle of the 19th century, some data about plant behavior could be found in books dealing with comparative psychology. The tendency gradually faded away, and the topic was almost exclusively treated in literature dealing with plant physiology. In recent years, however, there has been a revamping of psychological terminology and theorizing to describe, explain, and formulate hypotheses on the evidence that many of the sophisticated behaviors plants exhibit are an expression of cognitive competences that are generally attributed to human and nonhuman animals. In this work I shall discuss a selection of experimental studies supporting the idea that plants could be defined as cognitive agents. Experiments showing that the behavior of plants is controlled by a representation of its goal, episodic-like memory, and decision-making will be described. It is not, however, my intention to embrace any position as to whether or to what degree plants are conscious. Rather, I hope to (re)fuel the discussion within the psychological community that will point in the direction of integrating studies concerning adaptive plant behavior within the wider field of comparative psychology.

The coding of object thickness in plants: When roots matter.

“…In other words, the context in which the response is observed may ultimately be as important as the response itself. These findings nevertheless strongly support the idea that the root tip functions as a “command center” (Baluška et al, 2004) or, as recently pointed out, as a “cognitive center” (Baluška et al, 2009; Segundo-Ortin & Calvo, 2019; Castiello, 2021; Parise et al, 2020; Trewavas, 2009, 2016, 2017) implying that it is capable of processing multiple environmental cues providing information about the underground environment and leading to adaptive behavior. The idea is in line with the “root-brain hypothesis” of Charles and Francis Darwin (Darwin & Darwin, 1880) according to which each root apex acts as both a sensory organ and a “brain-like” command center generating specific cognition and behavior (Baluška et al, 2004, 2010).…”

“…The cases cited above provide a degree of support to speculative claims that some climbing plants are able to modify their circumnutation patterns to a greater or lesser extent depending on features of the stimulus targets with respect to what would be expected by chance movement (Raja et al, 2020; Tronchet, 1946, 1977). Experimental evidence demonstrating that this might indeed be the case has been forthcoming from recent studies that used kinematic analysis to characterize the movements of the tendrils of pea plants ( Pisum sativum L.) that appeared to be modulated depending on the features of the stimulus (Ceccarini et al, 2020, 2021; Guerra et al, 2019; for a review, see Castiello, 2021). Guerra and colleagues (2019), for example, recently demonstrated that pea plants ( P. sativum L.) are able to perceive a stimulus and to modulate the kinematics of the tendrils’ aperture depending on its thickness.…”

Root-To-Shoot Signaling for the Coding of Support Thickness in Pea Plants

“…The present results suggest a possible crosstalk between the above-and the belowground parts of P. sativum plants for the processing of the thickness characterizing a potential support. The integration of the information from both above-and belowground plant organs might provide the plant a full reconstruction of the surroundings, leading to a flexible adaptation of their behavior to ever-changing situations [41,[56][57][58]61,62,103].…”

“…Evidence from laboratory settings further demonstrates the support-thickness effects by using kinematic analysis to characterize the movements of Pisum sativum L. (from now on P. sativum) [37][38][39][40][41]. Guerra and colleagues [39], for example, demonstrated that P. sativum plants can perceive a support and modulate the kinematics of the tendrils' velocity and aperture depending on the thickness of the support.…”

Cracking the code: a comparative approach to plant communication

“…Independently of and beyond the anthropocentric tendencies that continue to exist, we are convinced that cognition needs to be approached from a wider biological perspective. It is now abundantly evident that plant behavior, which is more sophisticated than previously thought [ 4 ], reflects complex, flexible cognitive processes [ 1 ]. We are persuaded that the scientific community needs to spend efforts systematically investigating plant cognition, which shows unmistakable parallelisms with some forms of cognitive processing used by non-human animals, such as those underlying communicative processes.…”