I promise I’ll post a Friday puzzle later. But I just had to let you know that if you Google “water droplets burn leaves” (without quotes) you’ll get 436,000 hits as of this morning. Number 3 on the list? Our blog!
I think I’ll discuss this paper one more time on Wednesday – there are several other serious issues that I think are worth mentioning.
Have a good weekend!
I’ve got a good post for today…but have a seminar to give this morning and the blog has to wait. If you have time, go onto the web and look for “water drops burn leaves” or something like that. You’ll find reference to an article in New Phytologist that has the gardening world all a-twitter. I’ll be dissecting the paper – and the surrounding hype – later today.
You all remember the story of Chicken Little, right? Chicken Little thought she’d been hit on the head by a piece of the sky and ran around alarming the rest of the barnyard animals, who assumed Chicken Little knew what she was talking about. Had they not all been eaten by Foxy Loxy, I’m sure they would have felt foolish discovering that an acorn, not a piece of the sky, had bopped Chicken Little on the noggin.
On to today’s science rant.
Ann McCormick, one of my GWA (Garden Writers Association) colleagues, alerted me to an online story from Live Science entitled “Water Drops Magnify Sunlight and Burn Leaves.” A quick look at the internet shows that this report has gone viral, with similar headlines from other websites including the venerable Scientific American (“A study in the journal New Phytologist confirms the gardener’s belief that droplets of water resting on some types of leaves can focus sunlight until the plant’s surface actually burns”). It gets more and more ridiculous by the day (“Sun shining? Then don’t water your plants” courtesy of the Daily Mail in London; “Water droplets can form forest fires” from Calcutta). And so on.
I tracked down the original article in New Phytologist, entitled “Optics of sunlit water drops on leaves: conditions under which sunburn is possible.” You should take a look at it, if only to become completely intimidated by the physics and computer modeling it contains. I’ll be honest – I didn’t even try to understand this portion but focused on the plant science.
The authors had three actual experiments in addition to the optical modeling. The first experiment involved placing glass spheres on detached leaves (Acer platanoides – Norway maple) and exposing them to sunlight. Yup, glass spheres caused leaf burn on sunny days – no big surprise there. The second experiment substituted water droplets for the glass spheres and tested Ginkgo biloba as well as maple leaves. Not surprisingly (to me anyway) there was no damage to leaves of either species. The third experiment repeated the second, but tested the leaves of the aquatic fern Salvinia natans and voila! Leaf damage!
I have a lot of issues with this paper and maybe we’ll have to extend blog coverage for a day or two to keep today’s discussion as short as possible. Let me point out just two of the experimental problems
The leaves for experiments 1 and 2 were detached from the plant prior to treatment. How a detached leaf resembles anything in a natural situation is beyond me. Furthermore, these leaves were laid out, covered with glass spheres or water droplets, and left in the full sun for as long as nine hours. (Even so, the leaves covered with water droplets didn’t burn! You go, detached leaves!)
The Salvinia experiments were conducted on leaves scooped out of a pond, placed in two containers, sprinkled with water, and left in the sun for two hours. Then, in the authors’ words, “the experiment was concluded by cutting and scanning several Salvinia leaves – still holding water drops – in the laboratory in order to document their sunburn.” We are not told (a) how many leaves were scanned, (b) how the leaves were chosen, since they didn’t scan them all, and (c) how the reported damage was proven to be from water droplets. >Worse, there are no statistical data. We are simply asked to believe their report in the absence of any evidence except a handful of photographs. (As an aside, I really would like to know how they were able to cut and transport leaves without the water droplets moving!)
The lack of scientific rigor in this article is disappointing, especially in a peer-reviewed journal. Is there any plant scientist would consider detached leaves to be a model for those on an intact plant? Is there any gardener who would consider an aquatic fern comparable to trees and shrubs? Would any species – including aquatic ferns – easily burned by the combination of water and sunlight survive in the real world for long? I don’t think so – hence my myth posting on this very topic several years ago.
Let’s review: leaves of one species of aquatic fern was damaged by something – possibly sunlight – but without enough data presented to really evaluate the claim. None of the tree leaves tested were affected, even though they were detached from the plant and could not benefit from transpirational cooling. Yet the alarm has gone out! Don’t water your garden plants when it’s sunny, or the leaves will burn!!!
Be sure to take everything you read with a grain of salt – or an acorn.
(I will continue discussion of this article further if there is enough interest – that means you need to post a comment!)
Here’s Friday’s photo without my edits:
As you can see, there are tell-tale globs of hot glue around the base of the bud on the right. Hap was correct – it’s yet another “cactus strawflower” whose cactus portion had disintegrated, leaving only the strawflower graft behind. But out of context it could easily be mistaken for a bulb of some sort. Let the buyer beware!
OK, enough tormenting of my fellow GP. On to today’s photo challenge.
Is it a miracle? Is it a resurrection plant? How do you explain these large buds emerging from the soil?
A disclaimer: a portion of this photo has been Photoshopped. I promise the altered area was not of plant material. Monday’s answer will include the untouched photo in bigger context
This posting is for Holly, who I am sure is desperately trying to finish her annual review. I feel your pain! And I’m going to add to it today.
The poinsettia in these photos is not from this Christmas, but from 2008. You can see it thriving happily in its office environment. I’m told by its caretaker Nick (a nongardener) that it has no bugs or other problems, and seems very happy. And it’s blooming, without the benefit of the extended night period. (The post-it notes are instructions to its care when Nick is away.)
Apparently SOME people can easily grow poinsettias well past their expected holiday life span.
I’m pretty much a live-and-let-live person in terms of plant choices (as long as they’re not invasive). But I’m becoming convinced that oddities grafted onto hardy rootstocks are poor choices, because the rootstock always seems to win. I posted one of these several months ago (see October 28, 2009 ), but just today have just found the poster tree for my anti-rootgraft movement.
A little backstory. I’m currently out at the Washington coast, trying to get some writing and seminars done without disruption. Today I had to make a trip into Aberdeen, the horrors of which will have to wait for another post. Before going back to my retreat, I tried to renew my enthusiasm for life by seeking out bad plants. I was well rewarded.
I have to give my daughter Charlotte credit for spotting these lovelies. There were two of these $50 Betula pendula ‘Youngii’ trees available. I felt like I’d stumbled upon the next winner of “America’s Next Top Model.” I took pictures from every angle, full shots and close-ups, for your viewing enjoyment.
Note that the “unusual deciduous tree with pendulous branches” is a grafted tree, evidenced by the differences in girth at the grafting point. You’ll also note the appearance of vigorous watersprouts emerging from below the graft. (The bamboo stake to the left lost it function years ago, but is still adds an unexpected pop to the overall composition.)
And here she is in her full beauty! The “S” curve of the scion is bisected longitudinally by two watersprouts, forming a giant $! I do have to agree with the tag at this point – it certainly is “an excellent accent or specimen plant” for the Island of Misfit Grafts.
Finally, please enjoy yet a final reason I don’t like grafts:
(Hint: Note the glue glob.)
We have a winner! Brian correctly identified the windowed hood of a cobra plant (Darlingtonia) and its function in tormenting hapless insects. Here’s the entire picture:
Thanks to everyone who gave the puzzle a shot. Very imaginative guesses!
I’m taking the easy way out this week, as I’ve got to get my annual review done by next Monday (and I haven’t even started it yet. Hah!). But over the weekend, let’s see if you can figure out (1) what this is, and (2) why it looks the way it does:
Monday’s photo will reveal all!
David, one of our newer readers, asked why his red-stemmed roses seem to be more cold hardy than the green-stemmed cultivars. So today’s blog will be dedicated to a brief discussion of why it’s better to be red than dead.
The brilliant red, blue, and purple colors seen in flowers and fruits are due to anthocyanins (and the closely related betacyanins). These water-soluble, non-photosynthetic pigments are also commonly found in stems, leaves and other vegetative tissues. In 1999 I wrote a review article exploring the reasons that leaves and stems might turn red. A few years later I wrote another review, more specifically looking at how anthocyanins might influence plant water relations. (This last phrase is plant physiology-geek jargon, and I have to admit that the class I took on this topic during my PhD work was the hardest, and probably most hated, of all the classes I took. And now it’s turned out to be one of the most valuable. Go figure.)
While you hard-core types can read the review articles that I’ve hot-linked above, what I’ll try to do is summarize my hypothesis for why leaves (and stems) turn red. Some leaves are red when young, then turn green when older. Green, deciduous leaves turn red before they fall off in the autumn. And some plants are genetically programmed to have red leaves all their lives.
The environment can also influence leaf reddening. Drought, nutrient deficiency or toxicity, salts, heavy metals in soils, cold temperatures, low soil oxygen, whew! All of these environmental factors have been attributed to temporary reddening. What do these factors have in common?
It turns out that all of these environmental stresses directly or indirectly affect the ability of plants to take up and/or retain water. Because anthocyanins are water-soluble, they effectively dilute the concentration of water in the plant. Look at it this way: any limited area will only hold so many water molecules. A test tube of pure water has the maximum number of water molecules possible. A test tube of water plus sugar (or salt, or anthocyanins for that matter) will have fewer water molecules, because the other substances take up space, too. So effectively, anthocyanins reduced the apparent concentration of water in plant tissues.
Why is this important? Well, anthocyanins in leaves helps reduce water loss, because the concentration of water in the leaves is reduced and evaporation slows down. They also could serve as antifreeze compounds, allowing red leaves (and stems, David!) to be more cold hardy. And if anthocyanins aren’t amazing enough already, they also (1) bind and transport sugars during fall leaf color change, (2) protect tissues against high levels of solar radiation, and (3) are natural antioxidants. (That’s why you’re supposed to eat red fruits!)
I could go on and on, but I hope this might help explain why David’s red stemmed roses might be more cold hardy than the green variety. (And my thanks to my daughter Charlotte for allowing me to use her photos here.)
