Why are there “dew drops” at the tips of leaf veins?
❦ Have you ever seen clear orbs of water glisten along a leaf edge? You may have mistaken them for dew drops, which are caused by moisture from the air condensing on cool surfaces. But these drops are only found at the edges of leaves and if you look around- they won’t be found on dead leaves. So what are they?
❦ Plants use a plumbing system of xylem tubes to move water and nutrients. During the day, transpiration (water evaporation) from leaves creates a vacuum that pulls the column of water up from the roots to the leaves. At night, the stomata (leaf pores) close, transpiration stops and salts accumulate in the xylem of roots, drawing in water from the surrounding soil by osmosis. The excess water rises up the xylem tubes and is forced out at the leaf tips through openings called hydathodes. This exudation of plant sap is known rather inelegantly as guttation, and only happens at night. The water pressure is not strong enough to rise beyond 3 feet, so guttation is not seen on tree leaves. The thermal image (inset) taken by infrared photography shows the cooler temperature (blue) in the guttation droplets.
❦ When the drops dry, they sometimes leave behind a residue of salts and minerals. This is not a problem, unless the soil is over-fertilized resulting in fertilizer burn of leaf tips. In the same way, guttation droplets in corn seedlings were shown to have high levels of neonicotinoid compounds, used as pesticidal coatings on the seed. These concentrations could be a lethal dose for honey bees that sip on guttation drops as a water source. While shedding toxins through guttation drops protects the plant, it may have repercussions – both beneficial and harmful, on insects and other animals.
Inset of thermal image: http://thermal-imaging-blog.com/index.php/page/13/#.Vq1LIvkrLcs
REF on neonicotinoids in guttation droplets #openaccess: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4284396/
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Richard Taylor if it’s raining, I’m sure the runoff ends up at the leaf tips as well 🙂
https://goo.gl/photos/eShGmiM5vnuPqKLs7
That pic is of wheat grass
Ramesh Sistla grasses also show guttation, although none of the images is of wheat grass. Unfortunately, they’ve been shared too often to track down the original photographer, and I have to apologize for that. EDIT: oh I see, your photo in the linked comment is that of wheat grass. Got it, thanks!
Thanks Rajini Rao I had previously thought that surface tension had something to do with dews on the leaf tips.
That is fascinating. 🙂
I was unaware of the osmosis role in the cycle.
Thank you Rajini.
Merci pour ces explications passionnantes. Belle journée ou nuit à vous.
Fascinating information (and photos) Rajini Rao. I thoroughly enjoyed reading that! Haha…I can’t even explain how much..as satisfying as a favorite food!
Now that’s high praise indeed Debashish Samaddar 🙂
Great description and explanation. The way you wrote about the topic makes it more interesting.
Out of curiosity, why is guttation considered “inelegant”?
Nice
Johnathan Chung hah, you have caught me inserting my unscientific opinion into science writing! I think the word guttation sounds akin to guttural and not terribly pleasant. It’s not what I would use to describe these delicate beauties 🙂
As an adolescents in rural north India we, bunch of kids, used to sap on these dew drops on wintry morning dripping from wheat leaves thinking the were sacred and pure drops infused with some healing power. Much later in high school that could be explained scientifically to me but its sacredness remained engrained and enshrined in some synaptic knots in my brain. Reading your post gave a deja vu feeling and visit to memory lane!! Thanks Dr Rajini Rao
Dr. Umesh Yadav that’s a particularly evocative memory, thanks for sharing it here!
Remarquable…et intéressant…
Rajini Rao Oh ok, I didn’t want to assume anything. I figured you were thinking of “gutting”, so guttural is less gruesome in comparison 🙂 although inelegant would be an understatement for that…
Guttation probably comes from “guttae”, which means “drops” in Latin. I’m not sure if rain gutter comes from the same root or not.
(If you ever get a prescription for liquid medicine delivered by eye dropper, you might see the abbreviation “gtts”, akin to p.o., i.v., and other routes of administration.)
Johnathan Chung how interesting, I was wondering what the root word was, would not have guessed. I’ll keep an eye out for the abbrev. of guttae the next time I’m prescribed eye drops 🙂
I realize I never saw a drops like that with the Plants I have indoors…I wonder why? Are there plants that dont “gut”?
Good question, Rashmi Pahuja . I think there are two reasons: it’s not cool enough at night inside your home and the soil in the pot is probably not water saturated (that’s good!). Also, as you say, not all plants will show this (supposedly all “vascular” plants are capable of it). People have observed this in houseplants and become alarmed, judging by questions on gardening forums. Houseplants like Ficus, Diffenbachia and Philodendron can exude sap from leaf tips.
Ah! that makes sense. Thank you! for this info. Sometimes I never know what I am curious about, until I come upon something….I like reminders of being a child :).
Awesome post, Rajini Rao, and very timely. My 7 year old had a similar question. Thank you.
Curiosity is a wonderful thing at any age, especially fulfilling when we can find an answer 🙂 Rashmi Pahuja , Azlin Bloor
Rajini Rao indeed. I have used so many of your old posts with the kids,we truly appreciate them. 😊
Azlin Bloor thanks, I’m so glad to hear that!
Really clear and informative (and right up my alley). 🙂
Curious if you’ve noticed these in your potager garden or on grass, Michelle Beissel ?
If I did, I would have thought it was dew. I will keep a careful eye out for guttation. Rajini Rao.
Another refreshingly informative post. Thanks~^^
I never knew but also never saw this before. Thanks for sharing.
Rajini Rao You might be interested in this paper [ http://www.nature.com/articles/srep16790 ] about the height limit of a siphon. By degassing the water, they discovered that the siphon can reach greater heights and, as stated in the Summary, “These experiments also lend support to the cohesion-tension theory of sap ascent in trees.”
Beautiful
Kam-Yung Soh Ever since 1905, scientists have been debating how water reaches through the xylem to the top of tall trees. The cohesion-tension theory is one of the leading theories, and the complex structure of xylem bundles keeps the column of sap from breaking and prevents gas bubbles forming. Evaporation from leaves (transpiration) creates a negative pressure, keeping the sap moving. I found a historical overview here: http://plantsinaction.science.uq.edu.au/content/321-cohesion-theory-ascent-sap
This one looks like a great review, although I am unlikely to have time to read it: http://arxiv.org/pdf/1404.3066.pdf
Rajini Rao thanks a lot for clarifying this. The first time I noticed it was when I sowed some wheat last year so that the grass can be used to deck up our Golu (a colony of dolls put up during Dussera). At the time my children and I debated if these were dew drops; October was too early for dew but we thought may be dew came early! 🙂 And that is the picture I had put in the link. Apologies for not referring to it correctly. It is my own shot. Once more here for completeness.
https://goo.gl/photos/eShGmiM5vnuPqKLs7
Great answer, I agree MU-Peter Shimon .
Maybe this is connected to all the failing bees.
Rajini Rao I was 17 when I first understood this and found it so ingenious and magical!
nomad dimitri why am I not surprised that you were only 17 when you noticed this? 🙂
Christine Still not to all, but this could play some small part in declining bee population. Studies show many causes, including viral and fungal pathogens, mites and beetle pests, loss of habitat, pesticides, etc.
Johnathan Chung Rajini Rao
gTTS – Google Text to Speech
Aghhhhhh
I learned something new again, Nick James ! 🙂
Rajini Rao New, but a lot less shiny and interesting than the things you post:-)
Nick James as an aside, natural selection ensures that academics who survive have #shinyscience skills thanks to evolutionary pressures of grants, papers, and seminars 🙂
Rajini Rao As well as being charming people?
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Wow!!
Amazing! Can this happen anywhere in the world or with only specially shaped leaves?
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Now I know .thanks for the input.
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Rajini Rao So toxins in the guttation is what is poisoning/killing the honeybees
Mike Barzgari in some part. There appear to be multiple causes to honey bee declines, including viral and fungal pathogens, mites and beetle pests, loss of habitat, pesticides, etc.
Ahh so thats the cause of nutrient burn build up of salts cause burnt leaf tips from the droplets.
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Wow! And I thought it is something like perspiration !
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Hi Sonali Dalal , nice to meet you too 🙂 At any rate, it’s a lot prettier than our perspiration.
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At night, transpiration usually does not occur because most plants have their stomata closed. When there is a high soil moisture level, water will enter plant roots, because the water potential of the roots is lower than in the soil solution. The water will accumulate in the plant, creating a slight root pressure. The root pressure forces some water to exude through special leaf tip or edge structures, hydathodes or water glands, forming drops. Root pressure provides the impetus for this flow, rather than transpirational pull.Guttation fluid may contain a variety of organic and inorganic compounds, mainly sugars, and potassium
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Drops of DEW IS at the TIP OF leaf veins FROM LOving EASY AND FREE
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