The natural history of consciousness, and the question of whether plants are conscious, in relation to the Hameroff-Penrose quantum-physical ‘Orch OR’ theory of universal consciousness

Whether or not plants exhibit consciousness in the sense that they possess a ‘sensation of self’ is uncertain. Unlike humans and certain animals, plants cannot be interrogated directly on this matter. In any case, it is possible that states of consciousness, like brains and nervous systems of animals, have evolved and developed in different ways, depending on their phylogeny. However, some of the criteria by which consciousness is inferred to be present in animals are met by plants. For example, plants display features of cognition (sensing and response) and of learning and memory which, in animals, contribute to the conscious state. Plants also possess a rudimentary nervous system similar to that found in basal animals and have, perhaps, a simple brain, as well as showing slow and fast transmissable electrical activity, all of which are strong correlates of consciousness in animals. However, the question of consciousness in general can be approached in a different way. This is by taking the Orch OR (Orchestrated Objective Reduction) hypothesis of Hameroff and Penrose as a starting point. The Orch OR hypothesis, which is based in quantum physics, proposes that, when a sufficient mass of tubulin molecules has assembled into cytoskeletal microtubules (MTs) within neuronal cells of the brain, these structures become sites of quantum computation and of quantum state reduction (OR) events resulting in moments of protoconsciousness. Because plant cells also have large populations of MTs, and because plant MTs share properties with those of animal neuronal MTs, which putatively orchestrate OR events, plant MTs might also be sites of quantum reduction events and, hence, lead to momentary protoconsciousness. The extent to which the Orch OR hypothesis is applicable to plants is examined, and it is argued that, within the plant body, the most likely tissue where OR events could be located and promote protoconsciousness is to be found in the system of ray cells of tree trunks in which bundled MTs and actin filaments are prevalent. A single complete ray complex is estimated to contain about as many tubulin molecules as a single human cerebral neuron. Inferential evidence used by Hameroff and Penrose to support their Orch OR hypothesis leads in another direction. These authors presented estimates of the frequency of protoconscious or conscious moments. This frequency turns out to be similar to the frequency of successive Earthly quantal time units, according to a theory proposed by G. Dorda. These time units are also intimately linked with simultaneous changes of quantal mass, both mass and time being structured according to the motions of Earth and Moon around the Sun. In the case of cellular tissues, quantised mass takes the form of aggregates of water, and these are hypothesized to move in and out of cells in response to the passage of quantal time. In humans, the passage of time and its association with quantised water flux might account for a sense of self gained during meditative practices and govern also sleep-wakefulness rhythms, a principle which could apply to all living organisms. In plants, a similar quantised