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Science

Microscopic View of How Leaves Repel Water 33

Posted by Soulskill
from the make-like-a-tree-and-get-outta-here dept.
An anonymous reader writes: Years of research has gone into products that are hydrophobic — they resist getting wet. But nature solved this problem long ago, and it's ubiquitous outside our buildings and homes. You've probably seen it yourself, after a light rain: water collects in round droplets on many leaves from trees and plants, refusing to spread out evenly across the surface. This article explains why that happens using super slow-mo cameras and an electron microscope. "[T]he water isn't really sitting on the surface. A superhydrophobic surface is a little like a bed of nails. The nails touch the water, but there are gaps in between them. So there's fewer points of contact, which means the surface can't tug on the water as much, and so the drop stays round. ... [After looking at a leaf in the electron microscope,] we saw this field of tiny wax needles, each needle just a few microns in length! The water drops are suspended on these ultra-microscopic wax needles, and that keeps it from wetting the surface."
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Microscopic View of How Leaves Repel Water

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  • by Catamaran (106796) * on Saturday June 21, 2014 @04:04PM (#47289859)
    Garden Mythbusters: Does Sunlight and Water Mixing Really Burn Leaves?
    Two years ago, four Hungarian scientists published a paper called “Optics of sunlit water drops on leaves: conditions under which sunburn is possible” in the journal New Phytologist. Given the near-universal belief that water drops can scorch plant leaves on a sunny day (e.g. the RHS book How To Garden: “Under a hot midday sun, water droplets on leaves will act as miniature magnifying glasses and may scorch them”), you may be surprised — or you may not — that no one had previously checked to see if this actually happens.
    First of all, the short answer is no.
    Are there any circumstances under which water drops on leaves can cause sunburn? Yes, but only if the leaf has a dense covering of water-repellent hairs, in which case drops can be held above the leaf surface, allowing them to focus light on the surface itself.
    • by sumdumass (711423)

      I'm curious how this might happen. As the sunlight passed through the water droplet, wouldn't the water heat up, expand and change as a result losing the magnifying effect? Even if the light passing through didn't do it, sitting right next to the supposed burning surface would. Anyways, the heat can only get so hot and the water will evaporate.

      It just doesn't seem possible to me. Now, I know they say watering your lawn or garden in the mid day heat is stressful on the plants, but I was under the impression

      • by Bartles (1198017)
        How much do you actually think water expands per degree of temperature rise?
        • by sumdumass (711423)

          It's not much but not all water droplets magnify light due to surface tension and positioning of the droplets on less than smooth surfaces. So if it does happen to be one that would magnify light, the slight expansion would change the surface tension dynamics to some degree and thereby changing the shape of the droplet.

          This isn't about water growing in volume to some major size, it's about changing it's shape because it only acts like a concentrated magnifying glass when it has certain shapes present.

          Here i

      • by Khyber (864651)

        The smaller the lens the greater the magnification, typically.

        This will also depend upon the location of the light source. Overhead? No burn, most likely. 45 or 135 degrees? It's possible, depending upon the level of photon flux being concentrated onto a small spot, assuming the water droplet is even the correct size to project a clean focused on the surface of the leaf, given distance.

        • by sumdumass (711423)

          assuming the water droplet is even the correct size to project a clean focused on the surface of the leaf, given distance.

          That's where I think the major problem would be. As the water heats, changes within it's shape would/should occur. I don't think it could stay focused long enough to harm the plants. I know water on a windshield usually diffracts and reflects light making somewhat less pass through.

    • Garden Mythbusters: Does Sunlight and Water Mixing Really Burn Leaves?

      Two years ago, four Hungarian scientists published a paper called “Optics of sunlit water drops on leaves: conditions under which sunburn is possible” in the journal New Phytologist. Given the near-universal belief that water drops can scorch plant leaves on a sunny day (e.g. the RHS book How To Garden: “Under a hot midday sun, water droplets on leaves will act as miniature magnifying glasses and may scorch them”), you may be surprised — or you may not — that no one had previously checked to see if this actually happens.

      First of all, the short answer is no.

      Are there any circumstances under which water drops on leaves can cause sunburn? Yes, but only if the leaf has a dense covering of water-repellent hairs, in which case drops can be held above the leaf surface, allowing them to focus light on the surface itself.

      The point is moot.
      This question became a "Thing" mostly because of people growing pot in their basements. About 15yrs ago it became something you could do with nothing more than a trip to Home Depot. Unfortunately, due to draconian laws people are forced to hide this to the point the plants are usually grown in secret rooms, fake cabinents, etc... So the plant is in a very tight area, lots of humidity and questionable airflow. Because of this situation, watering became because of all the bending and manuver

      • by Reziac (43301) *

        Uh, no. It's been a "thing" as long as I can remember, and I started gardening in 1965. Vegetables, not pot.

        Camellias (the kind they sell at Home Depot, that make showy flowers) DO die back if they get water on the leaves in sunlight. Why I have no idea, but I lost several that way.

        As to the "bed of nails" -- when I was a kid I observed that if I rubbed a finger across the leaf surface, water would stop beading up, and the leaf would get wet. Well, now I know why -- I was crushing these microstructures. And

  • by ArcadeMan (2766669) on Saturday June 21, 2014 @04:29PM (#47289931)

    The screen will be covered with tiny microscopic wax needles.

  • by bmo (77928) on Saturday June 21, 2014 @04:45PM (#47289993)

    FTFA:

    Why would a plant evolve a method that cleans the under-side of its leaves?

    Come on, man, THINK for a second. What *else* might stick to leaves that the plant might not want? What about fungal spores? You know, organisms that might *eat* you if you were a tree? If you thought about it for a second, deciduousness in itself is a scheme to battle fungi too.

    This really is "missing the forest for the trees" or in this case, leaves.

    --
    BMO

    • FTFA:

      Why would a plant evolve a method that cleans the under-side of its leaves?

      Come on, man, THINK for a second. What *else* might stick to leaves that the plant might not want? What about fungal spores? You know, organisms that might *eat* you if you were a tree? If you thought about it for a second, deciduousness in itself is a scheme to battle fungi too.

      This really is "missing the forest for the trees" or in this case, leaves.

      --
      BMO

      Your poast is relying wholly on the assumption that water repelling abilities work the same way on microscopic spores as on macroscopic water droplets.
      You may need to revisit this assumption.

    • If you thought about it for a second, deciduousness in itself is a scheme to battle fungi too.

      I think you might be thinking too hard. Water conservation in colder climes/drought conditions is the most often mentioned advantage of flora shedding their leaves. I've never heard "battling fungi" mentioned as an advantage for "deciduousness" until now. http://en.wikipedia.org/wiki/D... [wikipedia.org]

      • by bmo (77928)

        A tree can't very well wash away an infection that has invaded its leaves.

        The only real way is to drop its leaves.

        If you've walked in the woods often enough, you'd see this.

        --
        BMO

        • by Reziac (43301) *

          Yeah, but then the leaves are around its stem or trunk, which is an even less-good place to get a fungal infection. Leaves can be shed; roots and trunks cannot.

          Deaves dry up before being shed (as water and nutrients are sucked out of them) and this generally applies to infected leaves as well, at any time of year. (Fall is not typically when fungal infections happen; rather, where spring rains and summer heat overlap.)

        • A tree can't very well wash away an infection that has invaded its leaves.

          The only real way is to drop its leaves.

          If you've walked in the woods often enough, you'd see this.

          -- BMO

          mmm..."infection" is quite a broader term than "fungi" - but I'll give you the benefit of the doubt that you're not moving the goalposts.

          In any case, may I suggest you ask yourself "what do leaves do, and how do they do it?" Then ask yourself "what are the conditions required for fungi to propagate?"

          After thinking about your answers, ask yourself why leaves would *ever* need protection from fungal infections.

          (hint: fungi infect trees through the roots/bark wounds for a reason)

  • Something like this would be a nice coating for:
      - Windshields
      - glasses
      - solar panels
    Unless, of course, it attracts grease...

  • by solanum (80810) on Saturday June 21, 2014 @07:43PM (#47290737)

    A bit of fun for those involved, but funnily enough plant science has actually investigated this over many decades. Go to a search engine of your choice and look up "waxy cuticle" and "trichomes". Sorry if I appear snide, but this is rather like someone posting an article about how they were amazed at what is inside their desktop PC, with photos and everything, as if no one had looked inside one previously. Neither the word cuticle nor the word trichome appear in that article, which shows they made no attempt to find out anything about their subject. Nice videos though, would be good for teaching!

    • True, this is nothing novel, but IT does incorporate cool electron microscope pictures and sweet slow motion video set to music, so It must be high tech.

      on the other hand, Its odd that this subject came up, because it instantly reminded me of this: http://www.realclearscience.co... [realclearscience.com] Because my first thought when I read the headline was "because they are fuzzy on a tiny scale" I know that the wax needles are a shade smaller than the 13 nanometers of amplitude that the researchers in the article I linked di
    • "Repeat" doesn't really sit well with me, because science is about repeating and confirming.

      I googled your suggestion, but I did not come up with anything that resembled this. Very loosely, if at all, but certainly not as described.

      So is there a specific result that demonstrates just how leaves place water above the surface so they can absorb stuff from the air without water interfering?

      Because that's what I took from this, and what I did not take from the first page of your suggestion.

      • Not just absorb stuff from the air, but keeping the leaves dry in a wet climate would help prevent the leaves from rotting.
  • by newcastlejon (1483695) on Saturday June 21, 2014 @10:27PM (#47291369)
    Are their articles usually written by 10 year olds?

    [Janine is] a super-skilled researcher, and she also has access to some of the coolest toys in existence.

    This person is supposed to be a professional writer?

  • It's long known that many plants produce a wax coating to help prevent the leaves from drying OUT when it's dry - the same surface system that keeps water out, helps (more importantly) keep water in.

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