PLANTS ARE AMAZING. Why do rhododendron leaves curl in winter, or morning glory or bean vines wind cleverly around a support on their way upward? Why does a crabapple bloom in spring and a chrysanthemum in fall—as if they can read the calendar? Why does one plant represent a feast for insects, when another right alongside is of no interest?
And though most leaves are green—why are some not green at all, or at certain times of year?
The new book, “How Plants Work: The Science Behind the Amazing Things Plants Do” answers those questions and more. (Enter to win a copy at the bottom of the page.)
Its author, Linda Chalker Scott, joined me on the public radio show and podcast to explain. Linda is an Extension Urban Horticulturist with Washington State University, and an associate professor of horticulture and landscape architecture there. You may know her as a collaborator on the popular Facebook page The Garden Professors, and a blog at extension.org by the same name.
Linda has her PhD in Horticulture and a double minor in biochemistry and botany – and a continuing passion for researching the latest developments and insights in all of the above.
Read along as you listen to the April 20, 2015 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).
read/listen: how plants work,
a q&a with linda chalker-scott
Q. So let’s forget the small talk, Linda: Shall we talk biochemistry instead? That’s where the book begins. I love how you talk about what you call “the plant’s personal pharmacy.”
A. That’s where plants have their real strength—the products that they can make in seemingly endless variety.
Q. You write that plants have a whole suite of chemicals they produce to protect against predation—against being eaten.
A. Think about eating certain parts of vegetables. Some might make you lick your chops, and others might make your tongue curl. A lot of those bitter things you find in vegetables are protective, and we tend to be odd in that we adapt to eating things that other animals wouldn’t. We like things that taste a little strange.
Q. Like cilantro—I always think of that as like, “Where the heck did that flavor come from?” [Laughter.]
So some chemicals that plants produce are repellents, and some are as strong as to be poisons, right?
A. Plants have a variety of ways to keep predators at bay, and repellents are ones that are usually airborne, and usually smell unattractive to at least some things, so the plants don’t even lose any tissues that way.
Q. Like garlic or onions?
A. Or mints that tend to be repellent to some insects. Things that we may like the smell of, some insects may not.
Q. So the next level of keeping things away that you write about after the repellents are the deterrents.
A. Those are the ones where something, like a deer, does go ahead and take a bite. There are a number of things that eat our garden plants that if they have a choice they won’t choose to eat the ones that taste bitter or nasty.
Capsaicin, for instance—there’s one good example, in chili peppers. That’s one that really keeps things, or at least some things, away—and again, we’re kind of weird in that we like that, but lots of other animals don’t.
Q. It’s supposed to deter squirrels, for instance. This winter squirrels decided chewing the wood on my back porch was a good idea. A concentrated form of capsaicin spray was recommended to give them a bite of something they didn’t like.
A. And did it work?
Q. No. [Laughter.]
A. It’s a desperation level—they get hungry enough they’ll eat anything.
Q. The squirrels asked me where the guacamole and chips were to go with the hot pepper spray. [Laughter.] It was a bad winter. But in most cases it would be a deterrent. And then there are also poisons that plants make, as we mentioned.
A. A lot of those are things we have come to depend on in medicine. Examples are a lot of the alkaloids, like nicotine or caffeine. We’d have to eat a lot of it to have toxic effects, but insects don’t’ really need to get much at all. Those are powerful potions, poisons, but again we’ve taken advantage of that and used them in our own pharmacies.
Q. Plants also have built-in chemicals to protect themselves against the environment, or environmental stressors.
Q. They’re my favorites, too—I love when things poke up from the ground displaying those pigments at the very start of the season, not just at leaf-peeper time in the fall. [Above, a species peony’s stem and leaves emerging in spring displaying non-green pigments.]
A. Anthocyanins are antioxidants, and there are other antioxidants, too. They obviously play an important role in the plants’ being able to quench oxygen radicals, which are very bad things for plants and people both. They make their own, and we can take advantage of that by eating tissues that are rich in antioxidants. Whether that actually translates to working in us, who knows, but it certainly isn’t going to hurt.
Q. With the anthocyanins, you write that they act as a natural sunscreen for the plants—which made me smile.
A. They do. They’ll absorb a lot of the radiation that could be harmful, especially at high levels. You have to think about what this whole “personal pharmacy” idea is: With us, it gets sunny outside and we can move into the shade, but plants can’t. Since they can’t move, they have to combat their environment with chemistry.
Q. Just like they can’t swat away an insect who’s nibbling, or an animal—so they need to have these chemical defenses in place.
I don’t have the expertise that you do, but for me it’s the awe thing, the awe factor, thinking about the evolutionary period during which all these things began, and what went on that caused these chemicals to be developed. The co-evolutionary strategies between plants and animals.
A. It really is an awe thing. The most amazing class I had as a graduate student was my plant biochemistry class, which they don’t teach in many places. I had a guy who has long since retired, whose knowledge was just amazing. But even he said: We probably haven’t discovered but 10 percent of the chemicals that plants make. The more it gets studied, the more we discover that almost every plant has some chemical they make that’s unique to the species.
Q. Unique to the species? Wow.
Let’s talk about the plants’ “clock”—like how crabapples know to bloom in the spring. And I say “know” not to anthropomorphize the plants, of course. [Laughter.] People talk about a “short-day onion,” for example.
A. It is fascinating, and we can mess up that clock just by the things we do around our gardens. Plants can’t tell time the way we do, but they can tell the difference in how much relative daylength and night length there is, and that’s pretty uniform from day to day, from year to year.
In other words, whatever is going to happen May 1 happens on May 1 each year, in terms of light-dark period. Temperatures may go up and down; rainfall may be high or low. But the one thing that is constant is how many hours of daylight you have.
Q. And therefore how many hours of darkness.
A. Exactly. When scientists first started looking at this, they noted that some plants bloom in spring or fall, and some have to wait till summer. They started distinguishing between short-day plants—the ones that bloom in the spring or fall—and the long-day plants (the ones that bloom in the summer), and then those that don’t seem to care, as long as everything else is sufficient in terms of temperature and water.
But the more they studied it the more they discovered it wasn’t so much the day period, it was the dark period that was important. The way they discovered this was interesting: They had plants growing in dark environments where they’d interrupt the dark period with a burst of light. When they did that, it could completely change the flowering of the plants.
When they did that, they learned that things we think of as short-day plants—spring bloomers, for instance—are actually long-night plants. Long-day plants are actually short-night plants. So if you took a long-night plant (short-day plant) and you interrupted its dark period, it wouldn’t flower.
Q. And that’s not “interrupted” as in: interrupted every night for many hours, but if you flick on the lights?
A. That’s all it takes—but it has to be pretty intense light. Moonlight doesn’t do this. A horror story I heard from a student one year, who was working at a greenhouse where they were growing poinsettias, which have to have very long, uninterrupted night periods or they don’t bloom: Some intern walked in the greenhouse and turned on the light and the whole crop was ruined.
Q. You hinted at this a minute ago, but what about some things we’ve done in our domestic environments, our cities and suburbs, by creating a lot more light at night. Has that changed how plants behave?
A. It really is enough to make a change—and you can even see it indoors, if you have a Christmas cactus, for instance. If it’s in a room that gets light at night, you’ll notice that the buds will form on the window side, which is darker, but not on the room side unless you keep on turning the plant.
If you have little garden pathway lights outside, that won’t make a difference; like moonlight, that’s pretty low-level light. But the high-intensity lights that they use for street lights and safety lights—those can really change a plant’s perception of time. Not only interfering with flowering, but actually with the plant going dormant in fall.
Q. There’s a fun section in the book called “Nasty Plants,” You really had fun with this book; you took all this science and had fun with it. But this section was about plants that had the suffix “-nastic.” Those curled rhododendron leaves in winter are an example of a “nasty plant,” yes?
A. We saw those a lot recently on our side of the country, too. We haven’t had nearly the winter you have, but the last couple of years here in the West we’ve been getting very cold temperatures very early in the season. So last year, in early November, we got some really low temperatures. I have a lot of rhododendron at my place, and I went outside and all the leaves were hung down and curled up like long cigars. That’s what is called thermonasty.
Q. [Laughter.] Thermo for temperature and nasty…
A. …-nastic is the movement.
Q. Oh—movement in response to temperature. It’s a protective mechanism, correct?
Q. And what about flowers that open and close by day and night? Is that another nasty?
A. That one’s called nyctinasty.
Q. Like tulips?
A. Yes, in the morning your tulip buds are closed, and in the daytime they open, then at night they close up again.
Q. That’s movement in response to light (as opposed to thermonasty, in response to temperature).
When we spoke the other day, you made me smile when you called these and some other terms “cocktail-party words,” that you can trot out. What kind of cocktail parties do you go to? [Laughter.]
A. Maybe that’s why I don’t get invited to many.
A. That one’s touch—and it is one of my favorite prefixes: thigmo-.
Vines move or grow in response to touch. If you think about it, normal plants have very thick or lignified trunks or stems, so they can grow upright and defy gravity, using chemistry [the lignin] to toughen their cell walls. But vines have floppy stems and don’t have the ability to grow upright, so they have to find support.
When they grow along the ground, they’re kind of twitching back and forth—and there are some really neat videos online of how plants grow in timelapse photography, and they do look amazingly alive.
A. Yes, they do. David Attenborough did some wonderful stuff years ago; his videos are fantastic to watch.
The vines will grow along the ground and twitch back and forth until they touch something that they can wrap around. Once they connect with something, they start growing in a circle around that support. What’s happening is that their cell division is really fast on the side that’s not touching the support—the outer part of the stem. Because it’s dividing faster it gets longer, so you get a curvature—it keeps curving around and around and around.
Q. So the pace of the cell division is different on the two sides of the stem, and that difference makes it grow unevenly, which is the curve. And that’s thigmotropism—in response to touch, it curves?
People may have heard of phototropism—moving toward the light—but this is influenced by touch.
A. Yes. It’s the same thing with the light: On the shaded side of the stem, the cell division is faster, so you get a curvature toward light.
A. That’s cleistogamy, or hidden flowers. They’re not the purple flowers that you see, but underground or under the mulch, and they’re white and they’re not pollinated.
Q. And that’s the source of the expression “shrinking violet”?
A. As far as I was able to find out—though that is of course not a scientific thing but a folklore thing. And they don’t do it the whole year; then the violets are flowering, you won’t find them. They usually happen near the end of the season.
Q. What does the word cleistogamy mean; does it have a translation?
A. It does, and this is why it’s such a great cocktail-party word: It means closed marriage.
Q. [Laughter.] So the shrinking violet has a closed marriage?
A. And the reason it’s called a closed marriage is since the flowers never open, all the pollination takes place within that closed flower—it’s self-pollinated. I think it’s one of the coolest words.
- My previous interview with Linda Chalker-Scott busts some myths about transplanting, about using mulch, and more.
prefer the podcast version of the show?
MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its seventh year in March 2016. In 2016, the show won three silver medals for excellence from the Garden Writers Association. It’s produced at Robin Hood Radio, the smallest NPR station in the nation. Listen locally in the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Eastern, rerun at 8:30 Saturdays. Or play the April 20, 2015 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).
enter to win the book
I’VE BOUGHT two copies of “How Plants Work” for two lucky readers. All you have to do to enter to win is answer this question in the comments box at the very bottom of the page, below the last reader comment:
What other plant phenomenon–like the ones described above that causes vines to twine or leaves to curl or insects to be deterred–do you wonder about, or know the “why?” of and the name for, but still find awe-inspiring? What about how plants work do you want to know (or share)?
Have no answer or just feeling shy? Simply say something like, “count me in” and I will, but an answer is even better. I’ll select two winners after entries close at midnight Monday, April 27 (U.S. and Canada only). Good luck to all.
(Photos from “How Plants Work.” Photo credits: p. 169 left, vines twining counterclockwise by Upupa4me; vines twining clockwise by Jennifer Boyer; Rhododendron leaves roll longitudinally by Nicholas A Tonelli; hidden violet flowers by Juliet Blankespoor. Anthocyanins by A Way to Garden. Disclaimer: Purchases from Amazon affiliate links yield a small commission.)