There is evidence that plant roots grow along moisture gradients. This is called hydrotropism; here's a link to a Trends in Plant Science review paper on it: <http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.129.6385&rep=rep1&type=pdf>. Following gradients is exactly what animals do when hunting by scent or sound, and I don't think anyone would object to the use of the word "seeking" in that context. So I think it's perfectly reasonable to say that plant shoots seek light and plant roots seek water (among other things).
Regards, Jane Shevtsov On Sat, May 21, 2011 at 1:01 PM, David L. McNeely <[email protected]> wrote: > ---- Amartya Saha <[email protected]> wrote: >> There are many experiments with pots divided into wet/dry and nutrient >> enriched/depleted zones, and most of them show greater root growth and >> density in wetter, high nutrient zones. >> The idea of consciousness is an animal-centric one; plants must be just as >> conscious in their own way, as ultimately a part of consciousness is >> recognition and adaptation to the environment, allowing species survival and >> reproduction. >> Genetically programmed to seek water -- don't all organisms seek water ? > > > If a seed or a seedling is planted in the dry zone of the above experiment, > roots will not grow into the moist zone. Only if the seed or the seedling is > planted in the moist zone will roots grow in the moist zone. > > Now, if the "dry" zone is sufficiently moist for that kind of plant, > including sufficiently moist to promote germination when using seeds, then > the roots will grow in the dry zone. When they reach the moist zone, there > will be increased growth. Such a result might appear to support the idea > that the roots "sought" the water. But in fact, they just grew more with > more water, less with less water. > > If you doubt that the statement is true, set up such an experiment and > determine the results. Let me know what you find out. > > What does "seek" mean? If you wish to define the word in terms of the above > experiment (which would not fit the normal meaning of the term) then you > might say the roots sought the water. But only roots actually in a zone > where moisture was adequate grew. I know of no experiments that have > demonstrated an ability of plant roots to grow from a zone of dryness toward > a zone of wetness due to some sensory mechanism. There are tropisms for > gravity, for surfaces, for light. I do not know of one for water, nor how it > would work. For that matter, true tropisms work by differential growth due > to unequal auxin distribution, so far as I know. > > mcneely > >> Sent on the Sprint® Now Network from my BlackBerry® >> >> -----Original Message----- >> From: "Pekin, Burak K" <[email protected]> >> Sender: "Ecological Society of America: grants, jobs, news" >> <[email protected]> >> Date: Sat, 21 May 2011 11:30:09 >> To: <[email protected]> >> Reply-To: "Pekin, Burak K" <[email protected]> >> Subject: Re: [ECOLOG-L] Communication Science to Public Plant Roots >> >> This seems to me more like a philosphical issue, rather than a scientific >> one. there are obviously several mechanisms that allow plants to actively >> "seek" water. However, unlike the mechanisms that allow an animal to seek >> water, such as detecting moisture in the wind using smell, they do not >> require a conscious desicion, i.e., the animal may decide to follow or not >> follow the scent, the plant does not have a choice. So the question is >> whether "seeking" requires a conscious desicion to be made by the >> individual. It could also be argued to what extent the desicions made by >> animals, such as humans, are conscious versus subconious and whether a >> subconcious desicion satisfies the definition of "seeking". >> >> -Burak >> >> >> Subject: Re: [ECOLOG-L] Communication Science to Public Plant Roots >> >> Well, I can't say what the narrator was basing his/her statement upon, but >> it can be justified. Roots are, for the most part, programmed to grow >> downward (positive geotropism), and in many if not most soil environments, >> water is more abundant at lower levels. Thus, growing downward means >> growing toward water. (One situation where this doesn't hold true is right >> after a rain, when the upper level of soil may be wetter then a lower >> level.) >> >> Additionally, roots (like all protoplasm-based structures) need water to >> grow. Thus, roots that are tentatively entering a wet zone (assuming it's >> not too wet) will grow faster than roots entering a dry zone, thus setting >> up a positive feed-back loop regulating root growth, which obviously has a >> genetic component. >> >> Finally, you may consider differential mortality of root cells in wet verus >> dry soil regions as also being a genetic program that causes the root SYSTEM >> to grow toward water. >> >> I think this is enough to justify the statement. Of course, the statement >> is a bit misleading in that it may call up the image of a little root tip >> sniffing first in one direction, and then in another, and finally saying, >> "Ah, the water's over there; I'd better grow in that direction." But this >> sort of imagery often colors our understanding of mechanistic processes in >> biology, even for scientists (for me, at least). >> >> Martin M. Meiss >> >> 2011/5/19 Wayne Tyson <[email protected]> >> >> > Ecolog: >> > >> > I just surfed across a "science" program on the "History" channel. The >> > narrator said "Plant roots are genetically programmed to seek water . . ." >> > >> > Will someone please inform me of the basis for this statement? >> > >> > WT > > -- > David McNeely > -- ------------- Jane Shevtsov Ecology Ph.D. candidate, University of Georgia co-founder, <www.worldbeyondborders.org> Check out my blog, <http://perceivingwholes.blogspot.com>Perceiving Wholes "In the long run, education intended to produce a molecular geneticist, a systems ecologist, or an immunologist is inferior, both for the individual and for society, than that intended to produce a broadly educated person who has also written a dissertation." --John Janovy, Jr., "On Becoming a Biologist"
