Pneumathodes?

[wirtlo]

Hi all. I didn't realize this 'science matters' forum was on here (pretty cool!), and I think its the perfect place to ask my question:

What are the white dots on orchid roots called (I've seen them on Angraecums, Phalaenopsis, and Dendrophylax)? I was curious as to their function, but I have to know what they're called before I can find that. The only thing I could find was a 1957 Dycus and Knudson article that mentioned them as "pneumathodes," and that didn't bring up much in a search.

Is there another name they go by? Or do you know what they do?

Thanks!

[tuvoc]

Maybe albino freckles? Sorry I can't answer your question, but just wanted to say 'Hi'. I haven't seen anyone else from Reno here until now.

Kim

[kavanaru]

Can you post any pics? I am not very sure to understand what you mean... I have even rechecked my Phals and they do not have "white dots"

[sucuz]

Never really noticed the "dots" before. Examined the roots of my phals and there were dots. Just watered this morning and many of the dark green roots had lines of spots that were more like dashes. They resembled "topstitching" along the seams of clothing. They were linear and followed the length of the root until they disappeared into silvery white as the vellum dried. Pores of some kind?

Different roots had some white mottling resulting from uneven drying as the roots returned to white, but I think that Wirtlo is referring to the "dashes" described above. Did not observe this on the thinner rooted orchids as mine tend to stay white when watered. If they are "spotted" or "dashed" also, it wouldn't show.

[wirtlo]

"They resembled "topstitching" along the seams of clothing. They were linear and followed the length of the root until they disappeared into silvery white as the vellum dried. Pores of some kind?"

Sucuz, thats exactly what I'm talking about! And I also don't see them on the thin rooted plants. I came across a description long ago, but can't recall what it said about them. Pore of some kind seems reasonable. Gas exchange for when the rest of the velamen is wet?

kavanaru, couldn't get a picture. I tried with my built-in computer camera but it wouldn't focus close enough to see the spots.

Here's a link to the only image I could find. It shows three 'dots' there, which seem larger and less numerous than the ones on my angraecoids, but it gets the idea cross.
red-weevil-2.jpg (image)

And Hi Tuvoc -- how're you and the plants enjoying the cloudy weather?

[sucuz]

Plant pores are stoma, plural stomata. Dictionary says that they are found on plant leaves (more thickly on the undersides) and on plant stems. Roots are not mentioned. Does not say that roots do not have them, the issue simply was not addressed. It says that the function is for the exchange of gasses.

[wirtlo]

Originally Posted by kavanaru

Can you post any pics? I am not very sure to understand what you mean... I have even rechecked my Phals and they do not have "white dots"

Originally Posted by sucuz

Plant pores are stoma, plural stomata. Dictionary says that they are found on plant leaves (more thickly on the undersides) and on plant stems. Roots are not mentioned. Does not say that roots do not have them, the issue simply was not addressed. It says that the function is for the exchange of gasses.

I was able to borrow a camera and get a nice close-up image of the spots on a Dendrophylax lindenii seedling. Here's the link:
Dendrophylax lindenii on Flickr - Photo Sharing!

I don't think they are stomata just because they are 'space' surrounded by two cells - which is really small and would be hard to see (although I think I can see stomata on bulbophyllum leaves - as they are on the underside and pretty evenly dispersed through out the entire leaf). I guess the spots could be a cluster of stomata. Still wish I had a name for these 'structures'.

Anyway, take a look at the picture link - I'm excited, it shows the spots really well!

[Ray]

In reading about vascular epiphytes, I came across the term "pneumathodes", and a Google search directed me back here, after all this time (last post was Nov 2008).

Sure enough, those are the white spots on roots, and they are apparently a non-saturating part of the velamen (and apparently it is unknown how they stay that way) that allows gas exchange to continue when the velamen is otherwise saturated and would block it, suffocating the roots.

[lepanthes89]

I dont have the definition, but etymologically the word is composed of pneuma - from the Greek,wind,air,breath,and thodes ,pertaining to.

[greenbean]

I remember this topic coming up before. Ray has it down. Pneumathodes function in the same capacity as stomata on leaves or lenticels on woody stems, aiding in gas exchange.