Question for photopro or any others.

Photopro, i direct this question mainly to you because you are the resident expert on aroids but if anyone else out there has input i would greatly appreciate it.

The question is fairly technical so here is some background for those who dont know. Xylem is that structure in a plant that governs the flow of water and minerals from the roots to the shoots.

So...
I was talking to a friend of mine who is a graduate student at the university where i currently go to school for nursing. I was hanging out with my friend in his office and i noticed that he had about a 5-6 foot cutting of a pothos and both ends were in water. I want to point out that this is a single cutting that has both ends cut and both of these cut ends are in water. This cutting is draped over a picture and the water sources are separate and there is a leaf node submerged in each of these glasses of water.

I asked my friend about his arrangement and he informed me that he felt that the two sources of water would help the plant avoid wilting while it rooted better than one source of water only at the base. I told him that i have never encountered a plant that had xylem that could transport water backwards along the stem and that one of the glasses of water would do nothing to provide water for the stem. We got into a discussion about plant physiology and ended up going to ask the nearest biologist.

This PHD had no idea. So we went to the best person on campus we could think of, the resident PHD of plant physiology.

The plant physiologist made alot of appropriate noises and tilted her head in thought and considered what we had asked and then just told us to stick only the one end in water. She never gave any real answer to the question about the flow of xylem.
It was nice that she chose to instruct us to do something that we had already thought of but we are still confused.

So i ask you or anyone else that may know this question ... Have you ever in your experience with aroids ever come across an aroid that has exhibited a backward flow of water. Other plants may exhibit this such as peperomias, begonias, klanchoe (although i am not certain of this either) but i have never known an ariod cutting that has sucessfully reversed the flow of its xylem to the point of yth cutting rooting and growing.

Any thoughts/comments?
Thanks all and sorry for the long story. ;)

 

Excellent observation! There are several plants that qualify for the common name Pothos but I'm going to assume you are speaking of Epipremnum aureum also known as Devil's Ivy. I've observed the same thing many times and frankly don't know the answer. But I'm going to try to find out by asking botanist Pete Boyce for an explanation. Pete has worked with this plant and may know more than any grower.

I have several very large specimens. Some have climbed up to 17 feet (almost 6 meters) to the top of my atrium and now produce leaves 16 inches in width. Once the plant reaches that height there is no place else for it to climb so it just begins to trail. And directly beneath that point is a 2500 gallon pond and once the plant hits the pond it sprouts many large root systems that drop deep into the water and then runs across the surface of the water until it find something else to root and climb.

I've actually got places where it climbs, drops into the water, climbs again to the ceiling, and drops back into the water. The plant is obviously picking up water from three ends, perhaps 4 since one one point it roots in the ground again before it climbs and drops back to the water. That total vine is probably well over 50 feet long!

My immediate guess would be the flow of water depends upon where the plant is capable of getting the largest volume! Obviously there is little volume up near the ceiling so I would guess it is sending water to the highest points from all the lowest points which are in water. In fact, it may be sending all the water upwards from the pond rather than from any of the points rooted in soil since the supply source would be much greater.

I'm going to forward your question to Pete and assuming he responds, and he normally does, I'll post his answer.

 

Steve but the end of your pothos hasn't been cut like riptide frog's though has it?
Even though it has rooted in water in four places at the "growing" end it is still growing, right?
IMHO, and I'm not a botanist by any stretch of the imagination, I don't think it could send water "backwards". The plant would be wanting to suck water from one end and grow from the other end.
Thats my take anyway. It will be interesting to see what Peter says...

Ed

 

Great questions! I don't know the answer, but I'm trying to find out. My plant was potted in soil as a very tiny plant. It then climbed up to the 17 foot level but at the 12 foot level began to send branches in all directions. The ones that went out over the pond then dropped back into the pond and sent out large root systems. Then it grew across to the soil again and climbed another side of the same post. Once it got to the top again it sent another runner back down to the pond. Interestingly, all the leaves up high are very large while all those near the ground or in the water are a great deal smaller.

I really don't know if all the water for the now massive plant is being collected only at the original root system. But I do know it has created some major roots down in the water. I sent the original question to Pete Boyce in Singapore but since his time is way ahead of ours, I'll have to wait for him to catch and read the question. Hopefully we'll get a response before long.

 

Here is my input. I am not a botanist or plant physiologist, but w/out a one-way valve system in the xylem, it's only logical that water would be drawn from the closest source based on osmotic gradients &/or tension produced in the xylem due to evaporation @ the leaves. Evolutionarily, it seems to make sense as well. Wouldn't vascular plants with the ability to sequester water from the closest source to a water deficeit be more likely to succeed? I think your answer would lie in the absence or presence of valve systems in the plant vasculature.

 

Very interesting point of view there Osmosisman. I can see what you are saying...some plants absorb moisture through the leaves also so hmmmm....

Ed

 

I had originally considered the lack of a valve system as well when i was discussing this with my friend. Upon this basis it would seem that water could come from any point along the stem and go in any direction.
However if one were to place a cutting in water or soil upside down would it root and send up new growth from the top, which would really be the plants bottom end, or would it start the new growth under the soil line or water line which would really be the plants top end. This of course broadens the question a bit and plant hormones may come into play at this point.
All i really know is that i have not had success when attempting to root a cutting that was placed upside down in its substrate.

 

The answer to that question is yes. You can take a cutting of any Philodendron stem and regardless of which end you place in the ground, it will produce new growth. Philodendron species also quite commonly produce new root systems along the entire length of the stem and they also take in moisture through their leaves. Since they are epiphytes they are trying to grab moisture from any source possible. I am still awaiting an answer from Pete but in the meantime have sent the same question to two other botanists. Someone will surely give us an opinion, and hopefully a scientific answer.

 

Don't have an answer yet, but I have a suggestion for an experiment from botanist Dr. Tom Croat of the Missouri Botanical Garden, "I think that the vessels work largely by capillary action and it probably would not matter which direction the stem was inserted into the water but I don't know for sure. It would be simple to prove the point. just stick two sample cuttings into a single body of water, one directed upward and directed downward then wait to see what happens."

I've still got the question out to several more aroid botanists.

 

I would absolutely love to see some pictures of this beast, by the way.

 

Very difficult to photograph, largely because my atrium is so crowded and overgrown but you can see a few here:

http://www.exoticrainforest.com/Epipremnum aurenum pc.html

 

I just went out and snapped one. The Epipremnum aureum has leaves almost 18 inches (46cm) while the adjacent plant, Philodendron sagittifolium, has leaves around 30 inches (76cm). The Epipremnum was a standard size "Devil's Ivy" with 3 inch (7.6cm) leaves when we planted it 6 years ago. The beam you see near the top is 12 feet (3.65 meters) off the ground. There are runners that have grown back to the pond and one of those again climbed the post and has again dropped a vine into the pond. The vines can easily reach more than 1 inch (2.6cm) thick.

 

This photo from photopro though very good doesn't begin to show how big some of this guys plants are!! I know, been there. It's amazing!!

 

I'm absolutely in awe! I would love to see this place in person, thank you so much for being so accomodating with the picture. What I especially love about it is that a standard Wal-Mart plant could be so wild, in the right enviroment. It's so beautiful!

 

Too bad you aren't closer. We had to cut quite a few large vines this morning since the plant was growing so fast. We threw away at least 5 or 6 that were 2 meters long (6 feet) with leaves at least a foot long (30cm). There just isn't anyone around here right now to give them a new home! But if you ever find yourself in NW Arkansas stop by, I can cut large vines just about any day of the year! We trim this thing at least once a month!

 

I am no Graduate Biologist, but about 1000 years ago I recall hearing that osmotic pressure allowed for a "lift" of about 32 inches, from one cell, in one direction, to the most extreme reaches allowed by the capability of that cell to "pump" liquid. Of course, there are uncounted cells in between one and the other, and each of these is adding its minute pressure to the 'stream', enabling food and water to reach the top of a 200 foot Sequoia, for example. It seems arbitrary, but I think I'm safe when I pose the presumption that 'there is a check valve capability of some kind' or there would be no ability for the first cell to push that first little bit of sap. My "Plant Bible", L.H. Bailey's 'The Nursery Manual', published originally in 1896, states unequivicably that cuttings (for example) do know up from down. His recommendation, incidently, is to lay Pothos flat, cover the nodes , and when a plant is growing from each, cut the stem fore and aft to end up with the same number of plants as you had nodes.

 

Very likely this is correct. But I've personally tried taking stem cuttings and potting them with the wrong end up and a new plant still grew. Somehow plants, at least Philodendron species, can accommodate and produce a new plant regardless of which end of the stem is placed in the soil.

 

I have not done much with aroid propagation. Working with Cissus quadrangulus whose sections are very symetrical (can't tell up from down unless marked) I have intentionally tried starts in both positions. The ones placed bottom down always sprout from the top. If placed upside down they invariably sprout from under the soil and never have I had one sprout from the "bottom" end which was sticking up. Don't know if this would be true for any other species. Just my 2 cents. Bill

Fascinating thread. Thanks guys!

 

I received this during the night from aorid expert Julius Boos, "I have NO idea! BUT--a few simple experiments might add some information, as Scindapsis or any other vining aroid are readily available. If I had the space and time I`d make a few cuttings say 12"-18" long, smaller that the one described. I`d place a couple of the cuttings ''head-down'' with the base cutting out of the water, and the cut-off top cut placed down into the water, this would test the ability of the shoot to absorb/ suck water from the top down (in this case UP!) and see if it could survive. I`d leave a few leaves on the shoot to be able to observe if and how fast they wilted/died or survived. You could have a couple ''controls'', the same sized cuttings in jars of water with the base cut in the water!

That`s about all I can suggest!"

Uulius has worked with aroid botanists on a number of scientific papers. Obviously, at least on a scientific basis, little experimentation has been done in this regard. But I have personally observed cuttings placed in both soil and water without regard to up or down. I can't say all survived, but certainly the majority did. Looks like you might have an interesting experiment to do and a paper to write!

 

Hey,

Thanks so much for the info and the prompt replies. It seems amazing to me that no one seems to know the answer to this question. It would seem that the function of xylem is one of the more basic of plant functions yet this aspect of it is not clearly understood. Oh well.

Just yesterday my friend and i started an experiment that is very nearly identical to the one outlined above. No conclusive results as of yet. :)

Thanks again, i heartily appreciate and respect your effort and interest.

 

I sure want to know what you learn with your experiments. You may well be on a field of aroid biology that has not been well researched. I say that because Dr. Tom Croat is recognized world wide as the top aroid botanist in the field! If he doesn't know, I'm not sure who might.

 

This is getting very interesting.
IMHO I think it depends on the species, it may work with Philodendrons but I know it doesn't work on say Cordylines, Dracaena and Crotons. Thats why I starting cutting the "bottom" on an angle because the cutting that did nothing I "presumed" were upside down. Maybe it was a coincidence. I didn't have any controls in place.

Ed

 

I am just adding my name so I get notified when next someone speaks. Fascinating stuff.
Liz

 

Glad to have you Liz. Maybe you can teach us something!

I think Ed is on to something here. It appears Philodendron sp. may be unique in their ability to grow from a cutting. I would suspect it is because, even though almost all home growers plant them in soil, in nature they often don't have a root even close to soil! I recently lost a very rare Philodendron species from French Guiana because I tried to grow it in soil! That plant is only known to exist in only two unique places in northern South America and in neither place does it grow with a single root in the soil!

Philodendron species are largely epiphytic plants and simply grow attached to a tree. They are often found as high as 60 feet (20 meters) and have no roots touching soil. Some species are terrestrial and interestingly, those are often very difficult to start from a cutting. One that comes to mind is Philodendron stenolobum which is easily lost if cut too soon. That plant, which is often sold under the name Philodendron williamsii (P. williamsii is a completely different plant) is a member of Philodendron section Meconostigma. And that group is the "tree" Philodendron species. They are capable of standing alone and often are found growing well away from trees. A species of Meconostigma that almost anyone has seen is a plant known by many as Philodendron selloum. That is a name no longer in use in science and is now correctly Philodendron bipinnatifidum.

The vining species sometimes end up on the ground as pieces due to a fallen tree, or a piece of the vine being cut. As a result, they have to struggle to survive and likely will set roots and begin a new plant by any means possible. Those are capable of growing in soil and are often technically known as hemiepiphytes. A hemiepiphyte can begin life as a seed (or cutting) on the ground and climb a tree, or as an epiphyte which eventually extends long roots down to the soil. Those roots can often be many meters long! My point is Philodendron species must be adaptable to survive in the rain forest. And they will survive by any means possible! Ever wonder why they will grow in water?

The Epipremnum originally asked about in this thread is not a Philodendron, but it is the South Pacific equivalent of a Philodendron and a relative. It has never been proven where the plants we all grow originated, but it was likely the Solomon Islands. And more than once I've started cuttings of that species by putting them in water without regard to which end was supposed to be "up".

To those who find this thread of interest, I'd certainly suggest you try Dr. Croat and Julius' experiment. No telling what we might learn together. And I promise, if these two gentlemen don't know the answer, it is an unstudied field!

And if you're interested in Philodendron stenolobum or Philodendron williamsii, check these links:

http://www.exoticrainforest.com/Philodendron stenolobum pc.html

http://www.exoticrainforest.com/Philodendron williamsii pc.html

 

Well as of saturday evening there was no noticeable difference in the turgidity of the leaves in the group that were placed upside down compared to the ones placed right side up in the water. No sign of rooting yet either, kinda early for that.
Its only been 3 days now and the plants are placed in artificial lighting so i wonder if we would see a difference in higher light due to enhanced transpiration. Thats for a future project though.
I'm going to check on them today to see if there is any change.
I'll keep you all posted as time goes on.