Calcutta, in the twenties. A mimosa leaf is tied by a thread to a lever mounted on jewel bearings, and every fifteen minutes an induction coil sends it a rigorously identical shock. The leaf falls, rises again, and the bent tip of wire that serves as a stylus engraves its curve on a smoked glass plate. The responses follow one another, equal. Then one of them sags, for no reason. Bose looks up towards the window and sees a shred of cloud passing across the sun. The plant had perceived the darkening he had not noticed.
That is the kind of scene Plant Autographs and Their Revelations is made of. Published in English in May 1927, published in French by Gauthier-Villars in 1934, it runs to twenty-seven short chapters, two hundred and thirty-six pages and one hundred and twenty illustrations. The preface is dated from the Bose Institute, October 1926. The dedication takes up three lines, to his wife, “who has stood by me in all my struggles”. Bose announces from the outset a work of popularisation, “a connected and popular account”, and he warns that he will take his reader step by step, in the order in which things appeared to him. No tables of measurements, almost no notes, no bibliography. The figures arrive in the flow of the sentence, one or two per experiment.
An autograph, and why that word
It all starts from graphology, which Bose treats with measured irony before turning to a precise example. At Hatfield House there are documents signed by Guy Fawkes, and those who have seen them declare that a sinister variation affects these signatures. Hence the leap: “perhaps the plant can be induced to give us its own autograph which would similarly reveal its internal condition”.
The programme that follows is the plan of the whole book, in three stages. Find the force that will make the plant sign. Convert that signal into a legible script. Then learn for ourselves the meaning of this hieroglyph. And he sets out his criterion of proof, which governs all the rest: “insisting that the only evidence which can be accepted is that which bears the plant’s own signature”.
The title is not a flourish. It is a ferocious technical constraint, and every apparatus in the book solves a problem of the same family, that of not weighing on what one measures. Animal muscle pulls hard, so the friction of the stylus against the glass does not hinder it. The mimosa pulls weakly, and the pressure of the tip is enough to alter the movement one claims to record. So Bose invents the Resonant Recorder: the stylus is tuned to vibrate a hundred times a second, like the string of a violin answering that of another violin, and it now touches the surface only in a succession of small taps. Friction disappears, and the benefit is twofold, since the trace becomes a series of dots whose spacing itself measures time. A hundredth of a second per dot, a thousandth on the finer models. This is how he times the latent period of a leaf: the shock at the vertical line, ten dots with nothing, the movement at the fifteenth. Seventy-five milliseconds.
That leaves the man. Bose expels him from the apparatus, and he writes it plainly: the plant must be excited automatically by an absolutely constant stimulus, produce its own record, go through its recovery and start the cycle again “without assistance or interference at any point on the part of the observer”.
What he makes the plants say
The book is one long enquiry conducted with instruments. The mimosa is put through the Sleep-Recorder, a set-up that questions it hour by hour for twenty-four hours, the plunging stem dipping into the mercury trough for only two tenths of a second so that the shock stays identical all night. Result: maximum excitability from noon to three in the afternoon, what Bose calls “the office hour”, gradual waking from eight o’clock onwards with this caption, “Note the human way in which it is trying to rouse itself gradually”, and a deep sleep that carries on after sunrise. The mimosa, he concludes, has anticipated the dissipated life of the modern Babylons, London, Paris and New York.
Drugs take up a whole chapter. Carbon dioxide suffocates the plant shut inside its glass chamber, and the caption of the trace says: “Note the gasp of relief when fresh air is introduced!” Ether puts it to sleep and lets it come back, chloroform in a strong dose abolishes everything and sends a brutal spasm upwards, alcohol exalts then depresses, with the only real joke in the book about the staggering gait one might exploit in a temperance lecture. And already the law that runs through the work asserts itself: a minute dose generally produces the effect diametrically opposite to that of a large dose.
The most novelistic chapter is the one about the Faridpore palm. An adult date palm, laid over at sixty degrees by a storm, rose again every morning and bowed every evening at the hour of the temple bells. Pilgrims came, cures were attributed to it, and the owner feared that the tree’s power might vanish at the profane contact of foreign-looking instruments. Bose lifts the objection by guaranteeing that the apparatus was made in India and that it will be installed by his assistant, a priest’s son. The continuous record destroys the common observation without destroying the fact: the tree is never at rest, its maximum erection is at seven in the morning and its maximum fall at three fifteen in the afternoon, so not exactly at the hour of prayer. The curve of movement is almost a replica of the thermal curve inscribed on the same plate, with a lag due to the inertia of the trunk. It remained to be proved that the movement was living and not physical. A year later, during a lecture chaired by the Governor of Bengal, a telegram arrives from Faridpore: “the palm-tree is dead and its movements have ceased”.
Then comes what existed in none of Bose’s earlier books, the crescograph. The tip of a shoot advances by about a hundred-thousandth of an inch per second, half a wavelength of sodium. Two levers in cascade amplify ten thousand times. Then Bose has the idea of lowering the plant at exactly the speed at which it rises, as a telescope compensates for the rotation of the Earth, and the recorder then dots a horizontal line that the slightest variation breaks. Finally he tries a third lever, fails because of weight and friction, and this failure drives him to the discovery: “Material contact having proved unworkable, I had to discover a new method of linking which would be immaterial and therefore frictionless.” The link becomes magnetic, without contact, and the amplification rises from ten to a hundred million. At a lecture, during an English winter, hibernating plants are drawn out of their lethargy and their growth is displayed by a line of light that travels across a ten-foot scale in twelve seconds.
The rest is a complete physiology. The Death-Recorder inscribes death as a function of temperature, with that convulsive spasm at sixty degrees beyond which there is no return. Cobra venom stops the plant’s pulse at one per cent, and accelerates it at one part in a hundred thousand. A platinum probe in a glass capillary, driven in by steps of five hundredths of a millimetre, goes looking for the nerve as one taps a submarine cable, and finds not one conductor but two, the external phloem and an unsuspected internal phloem. Hence the reflex arc of chapter XXVI, the sensory impulse coming in by one nerve and the motor impulse going back out by the other, six times faster. And the truest image in the book, the leaf that orients itself by four coordinated impulses, “like an anchored moth which turns towards the light”.
The ideas, including the fragile ones
The central thesis is not that sensitive plants exist. It is that they do not. The mimosa is merely demonstrative, because the lower half of its pulvinus is eighty times more sensitive than the upper one and the imbalance shows. Elsewhere, the opposing contractions cancel out and nothing moves. “Its seemingly rigid trunk is really a gigantic pulvinoid.”
Then comes the most original idea, the one that dissolves spontaneity. Since the leaflet obeys all or nothing, the surplus energy of a strong stimulus is stored, and it comes back out later in rhythmic pulsations. “The internal stimuli for such automatic movements are, in reality, external stimuli which have become trapped.” Bose verifies it both ways, by making an ordinary plant rhythmic and by extinguishing the telegraph plant that he cuts off from the energies of its surroundings.
One must also say what he does not do. In chapter III, he frankly raises the question of consciousness, quotes Bergson at length on consciousness being coextensive with life, then steps aside: “Leaving aside metaphysical questions on which authorities are so greatly divided, we shall deal with experimental facts and their implications.” He keeps Bergson’s criterion and spends the rest of the work showing that the plant satisfies it. The last chapter, on the power of the will to orient the molecules of a nerve, is openly speculative and it is the most dated. The book has another flaw, a real one: it never raises a serious objection against itself. The 1902 paper anticipated criticisms and answered them with an additional set-up, the 1927 one asserts. That is the price of the popular format.
One controversy nevertheless deserves reporting, because it is instructive. What Bose was criticised for in London was not first of all his measurements, it was his vocabulary. John Burdon-Sanderson objected to his writing response where, in his view, he should have written reaction, on the grounds that the first word granted too much agency to the plant. The Royal Society refused to publish his work on the electrical response of plants for more than a decade, before electing him a Fellow in 1920. And the existence of electrical signalling in ordinary plants, precisely what was being denied him, was established by a paper in Nature in 1992 on the wounded tomato, phloem transport totally blocked and the electrical signal passing all the same.
A word about the French edition, because it is a beautiful object. Gauthier-Villars, Poincaré’s publisher, brought out six Bose titles between 1926 and 1934. This one is the last, and it is translated jointly by Édouard Monod-Herzen, decorator and theorist of form, and by his son Gabriel, a nuclear physicist who would join the ashram at Pondicherry. One family will have carried Bose into French across two generations.
What I have kept from it comes down to one word, and that word is the title. An autograph is not a graph traced by a man who is watching. It is a trace with no human hand between the being and its signature. Bose spent forty years getting the observer out of the circuit, and he found in the end that the true laboratory was not the room full of instruments.
‘And beyond that arch, the Laboratory merges imperceptibly into the Garden, which is the true laboratory for the study of Life. […] Everywhere they will transcribe in their own script the history of their experience.’
Read in November 2016. Note written in 2026.
