roots dont absorb water?!!!

[digitalgate]

I am reading a book by Zdenek Jezek, from Rebo publisher. 2nd edition 2006. The complete Encyclopedia of Orchids
This is an abtract from the book.
The importance of Roots.

....The existence of aerial roots that hang down freely into space, has been
questioned by some botanist;in their opinion, this phenomenon only occurs if
a plant has insufficient life space and is therefore searching for a new
support.
It is only the young root tips that absorb water and minerals (hur?)
;the older parts are later covered with... velamen gives the dry roots their
white color, servingas an insulant and thus faciliatating water
savings...In wet weather , the velamen absorbs water and transmits more
light????!!(what is this!?) to the chlorophyll that is , to a limited extent,
functional even in older roots..

guys, is this true? This guys has a degree in phytotechnics and
phytogenetics from Brno University. I am very confuse about this comment in
his book.

I know older roots absorb water as well what he said is older roots don't ?
I read some research papers about root doing photosynthesis. It is proven.
but to "transmits light"????!!!

[Anton]

A lot of people have opinions, not ALL are correct, even those with degrees, as I will attest in my profession of Ophthalmology.

Take everything with a pinch of salt until others verify the same thesis.

[pikevi]

I think it would be right to say that not all parts of the roots absorb water and or minerals. Whether it be roots beneath the soil or aerial, only 'growing' parts of the roots have the potential to take part in 'osmosis', the process by which the nutrients and water are aborbed (through root-hairs).

Just like our skin (epidermis) the orchid roots are covered with a layer of tissue , velamen, I think and this layer is impermeable to water. I am not sure if it can allow xfer of moisture/nutrients when wet. It may behave just like our skin which is protected by about 6-8 layers of dead tissue that makes it almost impermeable to water . But once wet it WILL allow xfer of moisture and some chemicals too.

I have read that aerial roots in orchids are for absorbing nutrients. I still don't know if the entire surface of the roots can absorb moisture and nutrients in some cases. I doubt that very much.

I hope someone else will help you further.

[tom499]

I belief was that the aerial roots have an impermeable layer to reduce water loss, until the roots get wet, and the impermeable layer becomes transparent, allowing the roots to photosynethise, which would mean they have stoma to take in CO2 and release O2, with the side effect of losing water, so they only do it in high humidity, aka the aerial roots go green when you spray them.

But as said, they are all theories and need to be taken as such. It takes a long time for theories to become facts, so the author cant be proven right for some time yet.

But on the idea of this, the ghost orchid, and other leafless orchids do all there respiring and photosynethesis, and nutrient and water intake in their roots, so the roots must be capable of doing alot.

[kmarch]

He is saying:

1) One of the functions of velamen is to reduce water loss through the roots. I suppose that could be true, some of our biologists can address this question.

2) He's saying that when the velamen gets wet, it becomes translucent/transparent and allows light to reach the chlorophyll underneath. This is correct. On many orchids the velamen layer looks white when dry but becomes translucent or transparent when wet revealing the green layer of the root beneath.

3) I have heard the theory from others that orchid roots grow out into the air looking for something to anchor the plant too. It sounds possible. Others think roots grow into the air because the medium is stale or unpleasant in some way. Still others are of the opinion that roots grow into the air seeking moisture, trying to absorb it from humidity in the air.

So it would seem that some things in the excerpt are a matter of opinion, while other things are rather awkwardly stated, but correct. I had not heard that root tips absorb better than older segments of roots but whether true or not it probably willnot change the way I grow my orchids.

[PhalPal]

I think that all these theories and facts make the plant kingdom all the more fascinating.

[11Orchid126]

I find it interesting that soaking the roots for an hour or more in warm water make them more pliable. How can this be if they don't absorb water?

[Tobi]

The velamen is a multilayered structure composed of dead cells with special thickenings
in the cell walls. These thickings seem to prevent cellular collapse and provide the root
with some protection from cold and heat as well as mechanical injury. When the root
gets wet, the velamen fills with water, aided by perforations or tears in the walls from
when the roots went through a drying cycle. When the roots are dry, the velamen may
provide a barrier to water loss by way of transpiration from the wet, internal cells of
the root. From what I have read, and I may not know the most recent studies on
this, the aerial roots may serve as photosynthetic organs, but the reason of how
carbon dioxide diffuses into the root cortex and how the velamen influences light
transmission is still uncertain.

[evagentry]

I also read lately that only the tips of the roots absorb water and nutrients which was a little confussing, I think Kmarch said it well.