It's also worth mentioning that most tap water contains lots of dissolved minerals that are left behind when the water evaporates. This means that leaves that are frequently moistened and then let dry develop mineral buildups that can destroy their function. This problem is most acute in plants that take in a significant amount of water through their leaves. It can easily be fatal to things like bromeliads for which the leaves are the primary source of water uptake.

Patrick Alexander

In general, it sounds like a bad idea. Another drawback is that root acquired moisture will contain nutrients for growth. Foliage applied moisture does have what the plant needs. It is possible to foliar feed plants with fertilizer, but that is more often recommended as a quick fix for a nutrient deficit or soil problem. It is not intended as a long-term approach.

--Bob

Thanks for all your help!

I understand that there are two structures in the epidermis of plants called stomata and lenticels. These allow for the passage of gases.
Someone explain the mechanism by which foliage can take up water, fertilizer or pesticides unless it is in the form of a gas.
Sam

The mechanism: Water & its accompanying solutes are transported through the cuticle or epidermal cells of some leaves & twigs by diffusion, where it is adsorbed on the surface of plasmallene (a kind of protoplasm that forms cell walls) where, by osmosis, it passes through cell membranes to cytoplasm. In some plants, water is taken in through open stomata. How much water can be absorbed through leaf & twig tissues varies by species, & within species, cultural conditions have great influence. Ambient temperature, relative humidity, leaf senescence (age), light intensity, nutritional status of the plant all have impact on how readily water is taken in through leaves & twigs. Using a surfactant (wetting agent) also facilitates diffusion. The primary factor creating a barrier to diffusion through leaf cuticle tissues is the amount of (epi)cuticular wax present in epidermal tissues.

Al

With some plants, water absorption through the leaves is the primary way they get water. Bromeliads in general are such a group. PF

where it is adsorbed on the surface of plasmallene (a kind of protoplasm that forms cell walls) where, by osmosis, it passes through cell membranes to cytoplasm.

By plasmallene are your refering to the plasmalemma?

I posted from memory. It's not unusual for it to fail me when using uncommon words. Thank you for correcting me.

Al

Plasmalemma = Plasma membrane is the membrane that surrounds a cells protoplast. Perhaps you mean Plasmodesma which are holes in primary cell wall that allow the protoplast of different cells to be connected and surrounded by a single plasma membrane.

The pathway would be accross the cuticle first ... then either through cell walls ( apoplastic movement ) or accross the Plasma membrane and through the protoplast of different cells via plasmodesma ( symplastic movement ).

Good Day ...

I meant to say exactly what I said, except that I got a little inventive when I substituted plasmallene for plasmalemma. I'm not sure how I did that - I am familiar with the term, though I almost never have occasion to use it. Aside from that, I believe the info I provided is accurate.

Al

Just a little precision : in land plants water enters thru cracks and stomata into leaves. There is no way that water could cross a cuticle otherwise. Remember that a cuticle is made of long chain fatty acids that are hydrophobic, ie the repell water. So the only open doors are the stomata.
Naz

I agree .. but still .. leaves wilt with stomata closed ?? .. the low solubility of water in cuticle would suggest water does not move easily through cuticle... even more so with a thick cuticle.

I have seen detached Agave leaves go months with little wilt... still there is some cuticular transpiration... but not the route in general prefered for aquiring water.

Good Day ...

Now you've made me go searching. In a 1997 text by T. Kozlowski and S. Pallardy, "Physiology of Woody Plants", ISBN 0-12-424162-X, on page 234, under the heading "Absorption by Leaves and Twigs", it clearly states that water transport through epidermis is by diffusion. The text goes on to say that "In addition, some nutrients enter the intercellular spaces of leaves through stomatal pores" which leads me to believe this is a secondary path. This doesn't say, nor did I, that all plants are able to efficiently absorb water and/or solutes via foliar pathways. In fact, I stated the opposite in my first post with reasons following in one subsequent.

Since the question was asked about leaves, I limited my response to including them only, but lenticels and leaf scars along with cracks are also open pathways.

I'm not sure what purpose combing through minutiae looking for potential flaws serves, so unless Andy has an additional question directed to me, I'll happily move along. ;o)

Al

"I have seen detached Agave leaves go months with little wilt... still there is some cuticular transpiration... but not the route in general prefered for aquiring water"

Agave are CAM plants so stomatal opening and closing to prevent water loss is highly regulated. I vaguly remember a study of Opuntia wher the pads were hung out in the desert and lived for something like 7 years. The pads weren't taking up water but because they were CAM plants they were far better at managing the existing water in their tissue.

Hello Happy Hoe ...

I don't think CAM is playing a role here but the thick cuticle that some plants with CAM photosynthesis often have like Cactii and Agave ...

CAM plants open stomata at night which in a whole plant is a water saving scheme. The cut off leaf was inside and not exposed to sun.

Good Day ..

I wouldn't rule it out. Cam plant will open stomata in the day if water is plentiful and keep stomata closed at night when severly drought stressed. Also, suberization of the wound would decrease water loss that you would witness other plant material.

I'm late piping in on this one, so forgive me if you want it dropped and forever forgotten. It's been a long time since I've taken a plant anatomy or physiology class, but if memory serves me right, most plants take up little water through their stomata. Rather, wetting the leaves or misting plants increases humidity, slows transpiration and conserves water taken up by the roots. Remember transpiration is a physical process similar to osmosis (across a membrane) where water attempts to reach an equilibrium. In a dry environment water in the leaves is much more highly concentrated, so it diffuses through the stomata. That's why the leaves and stems of xeric plants often have a thick, waxy epidermis and sunken stomata, or are covered with lots of long trichomes having a fuzzy or hairy appearance. Both these conditions help slow transpiration by shielding the stomata from an arid environment. And yes, plasmodesmata are protoplasmic connections between adjacent cells - Really cool. Don't get me started...

I think it does take in water through its leaves because of the stomata.

Atacama Desert @ National Geographic Magazine
Although rain rarely falls on the Atacama's coastline, a dense fog known as camanchaca is abundant. The fog nourishes plant communities called lomas, isolated islands of vegetation that can contain a wide variety of species, from cactuses to ferns.

The leaves of a plant are covered in cuticles and stomata. The cuticles are a waxlike substance that waterproof the leaves, making it difficult for them to absorb water. The stomata are small pores that release water vapor and oxygen and, in turn, take in carbon dioxide. However, the concentration of the water vapor in the leaf drastically exceeds the concentration outside of the leaf (aka the humidity outside). This causes the water vapor to be 'sucked' out of the pores of the stomata (sing. stoma) and into the air, a process known as transpiration. As a result, water absorbed from the roots is pulled up the xylems (the plant's tissue that transports water) and distributed to the stem and leaves of the plant for photosynthesis to be achieved. To summarize, plants generally do not take in water through their leaves, but rely on their root system for this. There are some advantanges to watering a plant's foliage, such as preventing it from becoming too dry (and potentially becoming susceptible to fires), but also cleansing the plant of accumulated dust.

Patrick ./ paalexan
you said...

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"It's also worth mentioning that most tap water contains lots of dissolved minerals that are left behind when the water evaporates. This means that leaves that are frequently moistened and then let dry develop mineral buildups that can destroy their function. This problem is most acute in plants that take in a significant amount of water through their leaves. It can easily be fatal to things like bromeliads for which the leaves are the primary source of water uptake."

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I thought most plants benefit from foliar dressing,
which, it was my understanding, was basically minerals sprayed on the leaves with water ?

isnt most tap water have trace minerals like
Ca, Mg, iron, Cu ?