Wayne, I think the notions that have been expressed on the list represent semantic differences rather than differences in understanding how roots function. I think that those who have written accept the following:
Roots are hydrotropic, but the hydrotropism acts along a gradient, and acts over a very small distance. Rather than individual roots turning or growing toward water at some distant location, they grow differentially in different moisture fields. Whether one calls this behavior "seeking" or simply differential growth is dependent on one's application of the term to inanimate behavior or not. I can no longer speak for what is being taught, but I always taught that roots exhibit positive gravitropism but negative phototropism, while the shoot exhibits the opposite, and described classic experiments (and in elementary courses had students carry out such experiments) that demonstrate such behavior. Those tropisms do result in roots 'moving' toward moisture in soil. So far as hydrotropism, I did not teach it, because I did not recognize that the enhanced growth under higher moisture conditions compared to lower moisture conditions was a tropism. I now know that hydrotropism is involved, though it is minor compared to the differential growth along a gradient. I would teach that, were I still teaching. mcneely ---- Wayne Tyson <[email protected]> wrote: > Honorable Ecolog Forum: > > What does it matter, for the advancement of science and ecology in > particular, whether or not the root of the matter is resolved such that the > state of knowledge in this matter is articulated with clarity to the public > and those who inform the public (such as science writers, TV and movie > producers, reporters, etc.)? > > There seems to be at least two schools of thought (or at least opinion) > concerning whether or not roots are genetically programmed to seek water. > > What is actually being taught in the schools with respect to this issue? > What have you, as an ecologist, been taught and what do you teach (if you > teach)? > > WT -- David McNeely
