Monica Gagliano and the Experiments That Shook Biology

In 2012, Monica Gagliano was a successful marine ecologist at the University of Western Australia, publishing papers on coral reef fish and getting grants in a respected, uncontroversial field. Then she did something that nearly ended her career: she started talking to plants. Not metaphorically. Not poetically. She began investigating whether plants could learn, hear, and remember — cognitive capacities that mainstream biology had reserved exclusively for organisms with nervous systems. Within a few years, she had published papers that generated some of the most intense controversy in modern plant science.

Her story matters not just because of what she discovered, but because of what the reaction to her discoveries reveals about the limits of scientific paradigms and who gets to define the boundaries of consciousness.

Experiment One: The Mimosa That Remembered

Gagliano’s first landmark experiment, published in 2014 in the journal Oecologia, targeted the most fundamental form of learning: habituation. Habituation is the process by which an organism learns to stop responding to a stimulus that is repeatedly shown to be harmless. When you move to a house near a train track, you eventually stop noticing the trains. That is habituation. It has been documented in virtually every animal species studied, from flatworms to humans. It requires the organism to form a memory of the stimulus and make a judgment: this is not dangerous.

Gagliano chose Mimosa pudica — the “sensitive plant” — because it has a clear, measurable behavioral response: when touched or disturbed, its leaves rapidly fold shut. This is a defensive behavior, probably evolved to startle herbivorous insects. It is fast, dramatic, and easy to quantify.

She designed a custom apparatus — a rail system that dropped potted Mimosa plants 15 centimeters onto a foam cushion. The impact was enough to trigger the leaf-folding response but caused no physical damage to the plant. Each plant received seven sets of sixty drops in a single day. That is 420 drops per plant.

By the end of the first training session, something remarkable happened: the plants stopped closing their leaves. They had learned that the dropping stimulus was harmless and stopped wasting energy responding to it. This alone would have been significant. But Gagliano anticipated the obvious criticism — that the plants were simply fatigued, their folding mechanism physically exhausted — and designed an elegant control.

She shook the trained plants. Immediately, their leaves snapped shut. The folding mechanism was fully functional. The plants had not lost the ability to respond — they had specifically learned not to respond to the dropping stimulus while remaining responsive to a novel threat. This is the defining signature of habituation as distinguished from fatigue or sensory adaptation.

Then came the finding that truly stunned the field. Gagliano retested the plants twenty-eight days later. They still remembered. Nearly a month after training, the plants that had learned the dropping was harmless continued to keep their leaves open when dropped. Twenty-eight days of memory retention in a plant that typically lives less than a year.

For context, Caenorhabditis elegans — a nematode worm with 302 neurons and the most thoroughly mapped nervous system in biology — retains habituation memories for about twenty-four hours. Mimosa pudica, with zero neurons, remembered for twenty-eight days. The plant outperformed the worm.

Gagliano also discovered an environmental modulation of learning speed. Plants in low-light conditions — a more stressful environment where energy conservation is critical — habituated faster than plants in high-light conditions. They learned more quickly when the stakes were higher. This mirrors findings in animal learning research and suggests that the plant was not simply running a fixed biochemical program but was modulating its learning rate based on context.

The mechanism appears to involve calcium-based signaling cascades within plant cells. Animal neurons use calcium signaling as a key component of memory formation — calcium ions flooding into synapses help strengthen neural connections. Plants lack synapses, but their cells contain sophisticated calcium signaling networks that may serve an analogous function. The molecular hardware is different. The computational logic is strikingly similar.

Experiment Two: Pavlov’s Peas

In 2016, Gagliano pushed further into territory that made her colleagues deeply uncomfortable. She published a paper in Scientific Reports (a Nature journal) titled “Learning by Association in Plants” — a study demonstrating classical (Pavlovian) conditioning in garden peas (Pisum sativum).

Classical conditioning, first demonstrated by Ivan Pavlov in dogs in the 1890s, pairs a neutral stimulus (a bell) with a meaningful stimulus (food) until the organism responds to the neutral stimulus alone (salivating at the bell). It is considered a more complex form of learning than habituation because it requires the organism to form an association between two previously unrelated stimuli.

Gagliano designed Y-shaped mazes for pea seedlings. At the fork of the Y, the growing seedling had to “choose” which arm to grow toward. She attached a small fan and a blue LED light to the arms of the maze. During training, the fan (neutral stimulus) was always activated from the same direction as the light (meaningful stimulus — plants grow toward light). After three days of paired training, she removed the light and activated only the fan.

The results were striking: trained seedlings grew toward the fan — toward a stimulus that should have been meaningless to them — because they had learned to associate it with light. Untrained control plants showed no preference for the fan. The plants had formed a Pavlovian association: fan predicts light.

Even more intriguingly, when the fan and light were presented from opposite arms during training (fan from one side, light from the other), the plants learned that association too, growing away from the fan and toward where the light would be. They were not just responding to the fan — they were using it as predictive information about where light would appear.

This paper ignited a firestorm. In 2020, Kasey Markel published a replication attempt in eLife titled “Lack of Evidence for Associative Learning in Pea Plants.” Using a larger sample size and blinded analysis, Markel failed to replicate Gagliano’s findings. Gagliano and colleagues responded that methodological differences — including different growth conditions and maze materials — could account for the discrepancy. The debate remains unresolved. No other lab has published a successful replication, but no other lab has published using Gagliano’s exact methodology either.

This is science at the frontier: messy, contested, and uncomfortable. The outcome matters enormously. If plants can form Pavlovian associations, the implications for our understanding of consciousness are seismic.

Experiment Three: Roots That Listen

In 2017, Gagliano published another boundary-breaking paper in Oecologia: “Tuned In: Plant Roots Use Sound to Locate Water.” This study investigated whether pea plant roots could detect and respond to acoustic vibrations — specifically, the sound of water.

She grew pea plants in containers with two tubes at the base, giving roots a choice of two growth directions. Under one tube, she placed either actual running water, a recording of running water, or silence. Under both tubes, she tested various combinations of moisture and sound.

The roots grew preferentially toward the sound of running water — even when no actual moisture was present in the soil near the water source. The plants were detecting acoustic vibrations, not chemical moisture gradients, and using sound as a long-distance cue to locate water. The frequency range of maximum root response was between 200 and 300 Hz, with young roots showing clear bending toward a continuous 220 Hz tone.

When both moisture and sound cues were available, the roots used moisture preferentially — suggesting that sound serves as a long-range detection system (like hearing distant water), while moisture gradients serve as the close-range guidance system (like smelling water nearby). Two different sensory channels working in concert, with the plant switching between them based on distance to the target.

This was not the first evidence of plant acoustic sensitivity. Mancuso’s lab in Florence had demonstrated in 2012 that Arabidopsis roots grow toward sound sources. But Gagliano’s experiment provided the clearest evidence yet that plants use acoustic information for ecologically meaningful behavior — finding water, the most critical resource for survival.

The Backlash and What It Reveals

The scientific establishment’s reaction to Gagliano’s work has been instructive. Her papers have been published in reputable journals — Oecologia, Scientific Reports, Plant Signaling & Behavior. Her experimental designs include controls that address the most obvious alternative explanations. Yet the resistance has been fierce.

When she applied for funding from the Australian government, one peer reviewer wrote: “It’s very unlikely that plants are aware or conscious. So this entire project is meaningless.” Note the logic: the conclusion is assumed before the evidence is examined. This is not skepticism — it is dogma wearing the mask of skepticism.

Gagliano has described how journal editors rejected her papers not because of methodological flaws but because extending concepts like “learning” and “cognition” to plants was considered inappropriate — a category error. The pushback has not been primarily about data quality. It has been about who is allowed to be conscious.

In 2019, Lincoln Taiz and colleagues published a paper titled “Plants Neither Possess nor Require Consciousness” in Trends in Plant Science. Their argument was essentially definitional: consciousness requires a nervous system; plants lack nervous systems; therefore plants cannot be conscious. This is logically valid but empirically questionable — it assumes we know all the ways consciousness can be implemented, when in fact we do not understand how consciousness arises even in systems we know are conscious (like human brains).

Gagliano herself has not shied from the philosophical implications of her work. In her 2018 book “Thus Spoke the Plant,” she describes how her journey from marine ecologist to plant consciousness researcher was guided partly by dreams and direct experiences with plants — accounts that further alienated mainstream colleagues. She has been called a pseudoscientist by some and a visionary by others.

The Implications: What Counts as a Mind?

Strip away the controversy and look at what Gagliano’s experiments actually demonstrate:

1. Plants can habituate — they learn to ignore harmless stimuli while remaining responsive to novel threats (Mimosa, 2014).
2. Plants retain learned information for at least twenty-eight days — long-term memory without neurons (Mimosa, 2014).
3. Plants may be capable of associative learning — forming predictive associations between previously unrelated stimuli (peas, 2016, contested).
4. Plants use acoustic vibrations to locate resources — they hear, in a functional sense, and act on what they hear (peas, 2017).

These are cognitive capacities. Whether we call them “intelligence” or “consciousness” or invent new words to avoid those implications, the capacities themselves are real and measurable. A Mimosa that remembers for twenty-eight days that a specific stimulus is harmless is processing, storing, and retrieving information — the core operations of cognition — without any of the hardware we assumed was necessary.

The calcium signaling networks in plant cells, the action potentials that propagate through plant tissues, the neurotransmitter molecules produced by root tips — these are not brains, but they are computational systems capable of surprisingly sophisticated information processing. Evolution did not limit intelligence to neurons. It found other ways.

Gagliano’s work sits at the uncomfortable intersection where data challenges paradigm. The data says plants learn and remember. The paradigm says only organisms with neurons can learn and remember. When data and paradigm conflict, good science follows the data. History shows that paradigms eventually catch up.

One hundred years ago, the idea that bacteria could communicate was dismissed as absurd. Then quorum sensing was discovered, and now bacterial communication is a foundational concept in microbiology. Fifty years ago, the idea that animals had emotions was considered anthropomorphic projection. Now animal emotional research is a thriving field. Twenty years ago, the idea that octopuses were intelligent was treated as a curiosity. Now they are recognized as among the most cognitively complex animals on Earth.

Plants are next. Gagliano’s experiments are not the final word — they are the opening statement in a trial that will take decades to resolve. But the question she has placed before the court will not go away: If a plant can learn, remember, and respond to sound, then what exactly do we mean by mind, and are we sure we know all the forms it can take?