do aerial roots avoid light?

[Roberta]

Originally Posted by donna133501

Kind of hard to tell in a pic, but the pots on that fence all look level to me, and the one on the far left is actually tipped away from the direction the mass of roots are on??

Mine? That basket with all the new roots is nearly directly overhead. Any tipping is due to the camera angle, not quite straight up.

[donna133501]

No..I'm referring to the OP's pics, Dirty coconuts..her first pic she posted..in the background you can see her other orchids on a fence in pots, all have roots growing in the same direction as the plant she was asking about. I was wondering why their roots are also facing the same direction with no house to shade the roots or hold humidity? I was wondering if the roots could be growing away from hot afternoon sun, that's why I asked for the bearings, so I could see where west and south was relative to her plants in the pic.

[DirtyCoconuts]

Gotcha.

I’m a he, not a she, not that it matters for any real purpose.

The plants on the fence are not orchids they are lilies and the right (orientation) is the north and the wind wraps around the house pushing to the south there.

What look like roots are old dead leaves. I did that just for extra privacy

[ArronOB]

The plant hormone auxin governs directionality of the growing tip (root or stem) in combination with a bunch of other hormones.

Auxin can provide phototropic, geotropic or hydrotropic response, or any combination.

This is a good summary on hydrotropism : Hydrotropism - Wikipedia , which I believe has mainly been studied in plants with air roots, which can detect and grow towards the higher side of a humidity gradient. This mechanism is very sensitive and can be to a gradient we growers would have no hope of detecting with ordinary instruments.

I have never seen vandas growing in nature, but I often see their smaller relatives like sarchochilus that grow around here. They scramble, the roots nearly always angling back to the growing surface from which they get moisture, nutrient and stability. Some plants have a high percentage of roots growing in the air, particularly when there is a drop-off immediately below the plant, but this is not ideal and is associated with a high risk of desiccation in dry times.

So my view, yes, I would expect them to grow towards the nearest darker or moister surface. I think the response would be both phototropic and hydrotropic, but I believe the latter would be much stronger as a phototropic response seems to me to be just too easily fooled into a really unhelpful growth habit.

And yep, there must be a geotropic response going on as well, evidence by the fact the roots grow downwards, not up.

A mechanical hold is an inevitable byproduct of this strategy.

Coconuts, it’s time for you to do some experiments and maybe you could report your findings somewhere. I would do it but vandas grow so slowly in our climate we would never get to see the results.

Auxin - Wikipedia

[donna133501]

DirtyCoconuts..I apologize for my mistake.
ArronOB..great info, thank you.

[DirtyCoconuts]

Originally Posted by ArronOB

The plant hormone auxin governs directionality of the growing tip (root or stem) in combination with a bunch of other hormones.

Auxin can provide phototropic, geotropic or hydrotropic response, or any combination.

This is a good summary on hydrotropism : Hydrotropism - Wikipedia , which I believe has mainly been studied in plants with air roots, which can detect and grow towards the higher side of a humidity gradient. This mechanism is very sensitive and can be to a gradient we growers would have no hope of detecting with ordinary instruments.

I have never seen vandas growing in nature, but I often see their smaller relatives like sarchochilus that grow around here. They scramble, the roots nearly always angling back to the growing surface from which they get moisture, nutrient and stability. Some plants have a high percentage of roots growing in the air, particularly when there is a drop-off immediately below the plant, but this is not ideal and is associated with a high risk of desiccation in dry times.

So my view, yes, I would expect them to grow towards the nearest darker or moister surface. I think the response would be both phototropic and hydrotropic, but I believe the latter would be much stronger as a phototropic response seems to me to be just too easily fooled into a really unhelpful growth habit.

And yep, there must be a geotropic response going on as well, evidence by the fact the roots grow downwards, not up.

A mechanical hold is an inevitable byproduct of this strategy.

Coconuts, it’s time for you to do some experiments and maybe you could report your findings somewhere. I would do it but vandas grow so slowly in our climate we would never get to see the results.

Auxin - Wikipedia

What do you think i turn two around??

I can’t imagine it would HURT them and if it see them make giant U turns, then it supports the hypothesis

Also, if they go up or down to get there lol

[ArronOB]

Originally Posted by DirtyCoconuts

What do you think i turn two around??

I can’t imagine it would HURT them and if it see them make giant U turns, then it supports the hypothesis

Also, if they go up or down to get there lol

Well, no, not really. If you turn a couple around you still haven’t proven whether they are growing away from the light or towards the moisture - as we can almost assume both strategies would lead to growing towards the wall.

It gets confusing. One of the vanda-relatives that grow in our district has a certain percentage of aerial roots that grow upwards and outwards from the surface, in a loose tangle like a basket. Not surprisingly it’s called the tangle orchid. Apparently the role of these roots is to trap leaf litter, building shelter and moisture retention over the orchid. Presumably these roots are programmed to do the exact opposite of the rest of the same plant’s roots. Maybe vandas do the same, i don’t know.

[Roberta]

Quite a few orchids also will grow a set of roots that point upwards ("bird's nest roots) Some Cymbidiums, Ansellia africana, Den speciosum are examples. I figure that they're catching falling detritus for nutrition, also would be well positioned to capture morning dew.

[DirtyCoconuts]

i see the distinction between the two possible causes....i missed that the first read.....i suppose that i could add a reflective surface to the wall so the light was relatively equal and only the temp/humidity would be different but 1) that still leaves temp and humidity as variables and 2) mama Coconuts aint letting me mirror an outside wall of the house LOL

[Dollythehun]

Originally Posted by DirtyCoconuts

Gotcha.

I’m a he, not a she, not that it matters for any real purpose.

The plants on the fence are not orchids they are lilies and the right (orientation) is the north and the wind wraps around the house pushing to the south there.

What look like roots are old dead leaves. I did that just for extra privacy

I'm assuming you mean daylilies, Hemerocallis? Not Lilium?