Re: Anchomanes ID, root quest.

From: Jonathan Ertelt <jonathan.ertelt at vanderbilt.edu> on 1999.04.06 at 21:25:08(3240) At 3:11 PM -0500 4/5/99, Neil Carroll wrote: >Second question... > >I am having an argument on another list. Can anyone help me? I have never >heard of any plant anywhere that has roots that could be considered >phototropic. Is this a correct assumption?? > Neil, I believe that you are correct that there are no roots acting through phototropism. I don't think that roots which are responding negatively to gravity (I forget the term, but essentially anti-geotropic) as many orchids and some aroids, especially bird's-nest Anthurioum spp. do, in order to fashion a trash-basket root system, could be called phototropic. I haven't seen any studies done, nor noted any growth which would indicate that this is the response. Neither would luring roots with water towards a light source work for calling the roots phototropic. One would expect to see this especially with epiphytes, even more especially with leafless epiphytes, as has been mentioned, but that is not what you see - rather, the roots are generally following a moisture gradient. True, when moist, the roots will green up and become a photosynthetic organ, but moisture is key here, not light. Other examples of roots or root structures (which lets go the potato, a stem) which become photosynthetic upon exposure to light do not then continue to grow toward the light - at least I've seen no examples of this, and plenty where it is not what happens. Likely it is true we do not fully understand roots, or any other plant structure as fully as we can, but from all the evidence and suggested evidence presented, I think that you are correct in your assumption. - Jonathan Ertelt

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