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In his final book, The Power of Movement in Plants, Darwin wrote: “There are extremely few [plants], of which some part … does not bend toward lateral light.” Or in less verbose modern English: almost all plants bend toward light. We see that happen all the time in houseplants that bow and bend toward rays of sunshine coming in from the window. This behavior is called phototropism.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 13 | Location 138-141 2020-06-11 00:28:52
blue light is the primary color that induces phototropism in plants, while plants are generally blind to other colors that have little effect on their bending toward light.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 13 | Location 141-143 2020-06-11 00:29:04
In one simple experiment, published in 1880, the two Darwins proved that phototropism is the result of light hitting the tip of a plant’s shoot, which sees the light and transfers this information to the plant’s midsection to tell it to bend in that direction. The Darwins had successfully demonstrated rudimentary sight in plants.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 16 | Location 164-167 2020-06-11 00:31:39
Simply limiting the amount of light the plants saw was enough to cause Maryland Mammoth to stop growing and start flowering. In other words, if Maryland Mammoth was exposed to the long days of summer, it would keep growing leaves. But if it experienced artificially shorter days, then it would flower. This phenomenon, called photoperiodism, gave us the first strong evidence that plants measure how much light they take
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 18 | Location 181-184 2020-06-11 00:33:01
These experiments proved that what a plant measures is not the length of the day but the length of the continuous period of darkness.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 20 | Location 196-197 2020-06-11 00:33:59
Plants were differentiating between colors: they were using blue light to know which direction to bend in and red light to measure the length of the night.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 20 | Location 205-206 2020-06-11 00:34:42
you take irises, which normally don’t flower in long nights, and give them a shot of red light in the middle of the night, they’ll make flowers as bright and as beautiful as any iris in a nature preserve. But if you shine far-red light on them right after the pulse of red, it’s as if they never saw the red light to begin with.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 21 | Location 208-211 2020-06-11 00:35:19
It’s like a light-activated switch: The red light turns on flowering; the far-red light turns it off. If you flip the switch back and forth fast enough, nothing happens. On a more philosophical level, we can say that the plant remembers the last color it saw.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 21 | Location 212-214 2020-06-11 00:35:36
In nature, the last light any plant sees at the end of the day is far-red, and this signifies to the plant that it should “turn off.” In the morning, it sees red light and it wakes up. In this way a plant measures how long ago it last saw red light and adjusts its growth accordingly.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 22 | Location 218-220 2020-06-11 00:36:08
Phytochrome in the leaves receives the light cues and initiates a mobile signal that propagates throughout the plant and induces flowering.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 22 | Location 226-228 2020-06-11 00:36:41
So far we’ve seen that plants also have multiple photoreceptors: they see directional blue light, which means they must have at last one blue-light photoreceptor, now known as phototropin, and they see red and far-red light for flowering, which points to at least one phytochrome photoreceptor.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 23 | Location 230-232 2020-06-12 01:17:47
How do plants know when the spring has started? Phytochrome tells them that the days are getting progressively longer.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 26 | Location 261-262 2020-06-12 01:20:45
How do they know it’s autumn? Phytochrome tells them that the nights are getting longer.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 27 | Location 262-264 2020-06-12 01:20:52
Plants smell. Plants obviously emit odors that animals and human beings are attracted to, but they also sense their own odors and those of neighboring plants.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 33 | Location 308-309 2020-06-12 01:24:45
Gane analyzed the air immediately surrounding ripening apples and showed that it contained ethylene. A year after his pioneering work, a group at the Boyce Thompson Institute at Cornell University proposed that ethylene is the universal plant hormone responsible for fruit ripening.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 37 | Location 350-352 2020-06-12 01:28:46
The ethylene produced in ripening apples ensures not only that the entire fruit ripens uniformly but that neighboring apples will also ripen, which will give off even more ethylene, leading to an ethylene-induced ripening cascade of McIntoshes. From an ecological perspective, this has an advantage in ensuring seed dispersal as well. Animals are attracted to “ready-to-eat” fruits like peaches and berries. A full display of soft fruits brought on by the ethylene-induced wave guarantees an easily identifiable market for animals, which then disperse the seeds as they go about their daily business.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 38 | Location 359-364 2020-06-12 01:29:26
caterpillars were less likely to forage on leaves from willow trees if these trees neighbored other willows already infested with tent caterpillars. The healthy trees neighboring the infested trees were resistant to the caterpillars because, as Rhoades discovered, the leaves of the resistant trees, but not of susceptible ones isolated from the infested trees, contained phenolic and tannic chemicals that made them unpalatable to the insects.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 44 | Location 415-418 2020-06-13 01:07:11
Baldwin and Schultz proposed that the damaged leaves, whether by tearing as in their experiments or by insect feeding as in Rhoades’s observations of the willow trees, emitted a gaseous signal that enabled the damaged trees to communicate with the undamaged ones, which resulted in the latter defending themselves against imminent insect attack.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 46 | Location 431-434 2020-06-13 01:08:39
In other words, when a leaf is attacked by an insect or by bacteria, it releases odors that warn its brother leaves to protect themselves against imminent attack, similar to guard towers on the Great Wall of China lighting fires to warn of an oncoming assault.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 52 | Location 486-488 2020-06-13 01:13:57
A recent (and provocative) study in Science showed that men who simply sniffed negative-emotion-related odorless tears obtained from women showed reduced levels of testosterone and reductions in sexual arousal.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 58 | Location 545-547 2020-06-14 01:13:28
Burdon-Sanderson carefully placed an electrode in the Venus flytrap leaf, and he discovered that pushing on two hairs released an action potential very similar to those he observed when animal muscles contract. He found that it took several seconds for the electrical current to return to its resting state after it had been initiated. He realized that when an insect brushes up against the hairs inside the trap, it induces a depolarization that is detected in both lobes.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 70 | Location 645-648 2020-06-15 01:21:42
Studies revealed that when the electric signal acts on a group of cells called the pulvinus, which are the motor cells that move the leaves, it leads to the drooping behavior of the Mimosa’s leaves.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 73 | Location 675-677 2020-06-15 01:24:39
Normally, the protoplast contains so much water that it presses strongly on the surrounding cell wall, which allows plant cells to be very tight and erect and to support weight. But when a plant lacks water, there’s little pressure on the cell walls, and the plant wilts. By pumping water in and out of cells, the plant can control how much pressure is applied to the cell wall.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 74 | Location 683-686 2020-06-15 01:25:33
Of course, plants are exposed to multiple tactile stresses such as wind, rain, and snow, and animals regularly come into contact with many of them. So in retrospect, it isn’t so surprising that a plant would retard its growth in response to touch. A plant feels what type of environment it lives in.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 77 | Location 708-710 2020-06-15 01:27:56
An arabidopsis plant that’s touched a few times a day in the lab will be much squatter, and flower much later, than one that’s left to its own accord. Simply stroking its leaves three times a day completely changes its physical development. While this change in overall growth takes many days for us to witness, the initial cellular response is actually quite rapid. In fact, Janet Braam and her colleagues at Rice University demonstrated that simply touching an arabidopsis leaf results in a rapid change in the genetic makeup of the plant.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 78 | Location 718-722 2020-06-15 01:28:56
Thanks to the continuing work of Braam and other scientists, we now know that over 2 percent of arabidopsis genes (including, but not limited to, genes encoding calmodulin and other calcium-related proteins) are activated after an insect lands on its leaf, an animal brushes up against it, or the wind moves its branches. This is a surprisingly large number of genes, which indicates just how far-reaching a plant’s response is when it comes to mechanical stimulation and survival.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 81 | Location 758-762 2020-06-16 00:29:52
As sessile, rooted organisms, plants may not be able to retreat or escape, but they can change their metabolism to adapt to different environments.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 84 | Location 786-787 2020-06-16 00:32:30
Serious and reputable scientific studies have concluded that the sounds of music are truly irrelevant to a plant.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 107 | Location 983-984 2020-06-18 01:23:48
Dr. Lilach Hadany, a theoretical biologist at Tel Aviv University, uses mathematical models to study evolution. She proposes that plants do respond to sounds but that we have yet to carry out the correct experiments to detect their doing so. Indeed in science in general, lack of experimental evidence does not equate to a negative conclusion.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 107 | Location 986-989 2020-06-18 01:24:12
Scientists have documented that when a plant has been turned upside down, it will reorient itself in a slow-motion maneuver—like when a cat is falling and rights itself before it lands—so that its roots grow down and its shoots grow up.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 112 | Location 1029-1031 2020-06-19 01:18:38
We know because of our sixth sense, and contrary to popular belief the sixth sense is not ESP; it’s proprioception. Proprioception enables us to know where different body parts are relative to each other, without having to look at them.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 112 | Location 1035-1037 2020-06-19 01:19:35
With his makeshift centrifuge, Knight had applied a force on the seedlings that mimicked gravitation and demonstrated that the roots always grew in the direction of this centrifugal force—while the shoots grew in the opposite direction.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 117 | Location 1089-1090 2020-06-19 01:24:42
To test their hypothesis, they sliced off different lengths of the root tips of beans, peas, and cucumbers and then placed the roots on their sides over damp soil. While the roots continued to elongate, they no longer had the ability to reorient their growth and bend down into the soil. Even the amputation of only 0.5 mm of the tip was enough to obliterate the plant’s overall sensitivity to gravity!
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 118 | Location 1096-1099 2020-06-19 01:25:50
More than a century would pass before modern molecular genetic studies would confirm Darwin’s results, demonstrating that the cells in the extreme end of the root (in a region called the root cap) sense gravity and help a plant know where down is.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 121 | Location 1117-1119 2020-06-19 01:27:38
two distinct plant tissues detect gravity in the lower and aerial parts of the plant. In the roots, it’s the root tip; in the stem, it’s the endodermis. So while our “gravireceptors” are only in the inner ear, plants have them in many places in their root tips and in their stems.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 125 | Location 1150-1152 2020-06-19 01:31:43
Using a high-gradient magnetic field that simulates gravity, Kiss induced his statoliths to migrate laterally as if he had turned the plants on their sides. When this happens, the roots start to bend in the same direction that the statoliths move: if the statoliths move to the right, the root bends to the right; if the statoliths move to the left, the root bends to the left.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 126 | Location 1164-1167 2020-06-19 01:33:31
While plants have many different hormones, none are as prevalent or involved in as many processes and functions as auxin. One of these functions is to tell cells to increase their length. Light causes auxin to accumulate on the dark side, causing the stem to elongate on the dark side only, which results in the stem bending toward the light. Gravity makes the auxin appear on the “up side” of roots, which causes them to grow down, and on the “down side” of stems and leaves, causing them to grow up. While different stimulations activate different plant senses, many of the plant’s sensory systems converge on auxin, the movement hormone.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 129 | Location 1189-1194 2020-06-19 01:35:32
Darwin found that all plants move in a recurring spiral oscillation, which he termed “circumnutation” (Latin for “circle” or “sway”).22 This spiral pattern varies between species and can range from a repeating circle to an ellipse to a trajectory of inter- locking shapes much like the images from a Spirograph.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 131 | Location 1210-1213 2020-06-20 01:31:43
This revealed that gravity is not necessary for the movements, but rather modulates and amplifies the endogenous movements in the plant. Darwin was correct: as far as we know, circumnutation is a built-in behavior of plants, but this behavior needs gravity to reach its full expression.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 137 | Location 1268-1270 2020-06-20 01:36:52
Jaffe demonstrated that if he cut a tendril off of a pea plant but kept the excised tendril in a well-lit, moist environment, he could get it to coil simply by rubbing the bottom side of the tendril with his finger. But when he conducted the same experiment in the dark, the excised tendrils didn’t coil when he touched them, which indicated that the tendrils needed light to perform their magic twirling. But here was the interesting catch: if a tendril touched in the dark was placed in the light an hour or two later, it spontaneously coiled without Jaffe having to rub it again. Somehow, he realized, the tendril that had been touched in the dark had stored this information and recalled it once he placed it in the light. Should this storage and later recollection of information be considered “memory”?
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 143 | Location 1302-1308 2020-06-20 01:39:35
What’s fascinating is that the latest research hints that while memories are infinite, only a very small number of proteins are involved in memory maintenance.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 144 | Location 1319-1320 2020-06-20 01:40:38
Here, then, lies the proposed mechanism of the short-term memory in the Venus flytrap. The first touch of a hair activates an electric potential that radiates from cell to cell. This electric charge is stored as an increase in ion concentrations for a short time until it dissipates within about twenty seconds. But if a second action potential reaches the midrib within this time, the cumulative charge and ion concentrations pass the threshold and the trap closes. If too much time elapses between action potentials, then the plant forgets the first one, and the trap stays open.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 148 | Location 1361-1365 2020-06-20 01:44:45
Plants are acutely aware of the world around them. They are aware of their visual environment; they differentiate between red, blue, far-red, and UV lights and respond accordingly. They are aware of aromas surrounding them and respond to minute quantities of volatile compounds wafting in the air. Plants know when they are being touched and can distinguish different touches. They are aware of gravity: they can change their shapes to ensure that shoots grow up and roots grow down. And plants are aware of their past: they remember past infections and the conditions they’ve weathered and then modify their current physiology based on these memories.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 170 | Location 1559-1563 2020-06-24 01:50:06
plant’s awareness also does not imply that a plant can suffer. A seeing, smelling, feeling plant can no more suffer pain than can a computer with a faulty hard drive. Indeed, “pain” and “suffering,” like “happy,” are very subjective terms and are out of place when describing plants.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 172 | Location 1577-1579 2020-06-24 01:51:14
The construct of a brainless plant is important for me to accentuate. If we keep in mind that a plant doesn’t have a brain, it follows then that any anthropomorphic description is at its base severely limited. It allows us to continue to anthropomorphize plant behavior for the sake of literary clarity while remembering that all such descriptions must be tempered by the idea of a brainless plant. While we use the same terms—“see,” “smell,” “feel”—we also know that the overall sensual experience is qualitatively different for plants and people.
<What a Plant Knows>(Chamovitz, Daniel) Highlight on page 173 | Location 1587-1591 2020-06-24 01:52:17