Saturday, June 09, 2012
  What a Plant Knows

In the last few months I've been thinking and writing a lot about plants, and acquiring a new respect for their talents. My overall view of life has expanded to encompass the plant-y way of doing things. Before this I had simply paid no attention to plants and knew nothing about them. They're green. Some of them taste good. That was about it.

Realized last week that I've been walking into territory already claimed by Daniel Chamovitz. I immediately got his book What a Plant Knows. Reading it gives me the intellectual tickles!



Chamovitz has been opening his mind in the same direction, and the book is a careful exploration of current knowledge about plant 'thinking', never going beyond what has been strictly observed and experimented. Some of this knowledge has been familiar forever to farmers and gardeners, but the internal details have only recently been uncovered.

The plant versions of sight, smell and touch are unfamiliar, and Chamovitz fills in plenty of surprises, such as how plants sense exactly the right colors to distinguish sunrise from sunset, or how one leaf tells another leaf to get ready for an insect attack.

The 'muscles' of alfalfa and clover, which I've been marveling about, are not nearly as amazing as the touch response of mimosa. Plants don't use explicit neurons and muscles; instead they run the same electrochemical processes in more generalized cells.

Chamovitz's 'life-view expansion' goes farther than mine in some ways and not quite as far in others. I suspect the not-so-far parts result from insufficient knowledge.

For instance, his account of proprioception and balance is complete, and his overall life-view is fully expanded in that area. His analysis of hearing (which involves some of the same organs) is incomplete, and he's unwilling to extend the analogy there.

Plant proprioception is familiar: seeds obviously know how to send roots downward and shoots upward. Anyone who has thought even briefly about plants has realized there must be a mechanism... but how does it work?

Amazing answer:
How do these specific groups of plant cells in the root tip and in the endodermis sense gravity? The first answers came from microscopic studies of the root cap... Cells in the central area of the root cap contain dense ball-like structures called statoliths, which -- similar to the otoliths in our ears -- are heavier than other parts of the cell and fall to the bottom side of the cells.


In discussing the human version of hearing Chamovitz makes one important mistake, which may lead him to underestimate the potential of plants. He says:
The hair cells in our ears convey two types of information: volume and pitch. Volume is determined by ... the amplitude of the sound waves reaching our ears. The higher the amplitude, the more the stereocilia [on the hair cells] bend. Pitch, on the other hand, is a function of frequency. The faster the frequency of the incoming wave, the faster the stereocilia bend back and forth.


Nope, that theory was rejected 60 years ago ... along with a directly parallel bad theory about speech.

What really happens in the cochlea is much more astonishing.

Here's the outer and middle ear responding to an incoming sound wave. The changes in air pressure cause the eardrum to move in and out (in real life MUCH smaller moves than shown here!) and the moves are transferred through the three tiny bones into the snail-shaped cochlea.




Here we have a schematic version of what happens inside the cochlea. The stapes (stirrup) moves in and out, causing a pressure wave in a fairly dense and viscous fluid. The hair cells are between the upper and lower parts, with their sensitive ends effectively reading the width of the upper part.


The wave goes around the bend, then bounces off the 'back end' of the chamber. Interference between the forward and reflected waves results in a standing wave in the upper part of the chamber, pushing against the hairs.


Here's the same schematic with a higher frequency. Note that the standing wave moves closer to the stirrup when the pitch is higher. A different set of hair cells are now being pushed by the upper part of the cochlea. Thus we sense frequency by determining which part of the cochlea is moving, not by counting the actual moves.



Could a plant also use a 'place response' to detect an interesting sound? The mechanism could involve the same statoliths that sense orientation. A low rumble in the earth might be interesting to a plant because it indicates gophers or water-table movements. The low-frequency wave would move the roots slightly; the statoliths would tend to hold still by inertia, and their relative movement within the cell could be sensed. Roots of different diameters would tend to resonate at different frequencies. An earlier thought on plant hearing.

= = = = =

At the end Chamovitz pulls it together in an epilogue, with a summary of the analogies and a caution against too much anthropomorphizing.
The construct of a brainless plant is important. If we keep in mind that a plant doesn't have a brain, it follows that any anthropomorphic description is at its base severely limited. While we can use the same terms -- "see", "smell", "feel" -- we also know that the overall sensual experience is qualitatively different for plants and people.

Hmm. Not sure about that. Seems to me that Chamovitz is actually doing the anthropomorphizing here, in assuming that a centralized brain must exist in order to have things like awareness, attention, and suffering. Those phenomena can't be externally observed. We may be able to identify specific centers in our brains that correlate with those emotions, but that doesn't tell us anything about the internals of other critters. (The fact that our moods are partly controlled by the bacteria in our colon should inspire humility!) We assume, probably accurately, that our fellow social mammals share most of those qualities because we can translate their external signs and cues pretty well. But that's just an assumption, and there's no objective reason to declare that those qualities are absent because the external cues are absent, nor because our peculiar form of centralized neural structure is absent.

Labels: ,

 


<< Home

blogger hit counter
My Photo
Name:
Location: Spokane

Polistra was named after the original townsite of Manhattan (the one in Kansas). When I was growing up in Manhattan, I spent a lot of time exploring by foot, bike, and car. I discovered the ruins of an old mill along Wildcat Creek, and decided (inaccurately) that it was the remains of the original site of Polistra. Accurate or not, I've always liked the name, with its echoes of Poland (an under-appreciated friend of freedom) and stars. ==== The title icon is explained here. ==== Switchover: This 2007 entry marks a sharp change in worldview from neocon to pure populist. ===== The long illustrated story of Polistra's Dream is a time-travel fable, attempting to answer the dangerous revision of New Deal history propagated by Amity Shlaes. The Dream has 8 episodes, linked in a chain from the first. This entry explains the Shlaes connection.

My graphics products:

Free stuff at ShareCG

And some leftovers here.

ARCHIVES
March 2005 / April 2005 / May 2005 / June 2005 / July 2005 / August 2005 / September 2005 / October 2005 / November 2005 / December 2005 / January 2006 / February 2006 / March 2006 / April 2006 / May 2006 / June 2006 / July 2006 / August 2006 / September 2006 / October 2006 / November 2006 / December 2006 / January 2007 / February 2007 / March 2007 / April 2007 / May 2007 / June 2007 / July 2007 / August 2007 / September 2007 / October 2007 / November 2007 / December 2007 / January 2008 / February 2008 / March 2008 / April 2008 / May 2008 / June 2008 / July 2008 / August 2008 / September 2008 / October 2008 / November 2008 / December 2008 / January 2009 / February 2009 / March 2009 / April 2009 / May 2009 / June 2009 / July 2009 / August 2009 / September 2009 / October 2009 / November 2009 / December 2009 / January 2010 / February 2010 / March 2010 / April 2010 / May 2010 / June 2010 / July 2010 / August 2010 / September 2010 / October 2010 / November 2010 / December 2010 / January 2011 / February 2011 / March 2011 / April 2011 / May 2011 / June 2011 / July 2011 / August 2011 / September 2011 / October 2011 / November 2011 / December 2011 / January 2012 / February 2012 / March 2012 / April 2012 / May 2012 / June 2012 / July 2012 / August 2012 / September 2012 / October 2012 / November 2012 / December 2012 / January 2013 / February 2013 / March 2013 / April 2013 / May 2013 / June 2013 / July 2013 / August 2013 / September 2013 / October 2013 / November 2013 / December 2013 / January 2014 / February 2014 / March 2014 / April 2014 / May 2014 / June 2014 / July 2014 / August 2014 / September 2014 / October 2014 / November 2014 / December 2014 / January 2015 / February 2015 / March 2015 / April 2015 / May 2015 / June 2015 / July 2015 / August 2015 / September 2015 / October 2015 / November 2015 / December 2015 / January 2016 / February 2016 / March 2016 / April 2016 / May 2016 / June 2016 / July 2016 / August 2016 / September 2016 / October 2016 / November 2016 / December 2016 / January 2017 / February 2017 / March 2017 / April 2017 / May 2017 /


Major tags or subjects:

Carbon Cult
Defensible spaces
Ethics
Experiential education
Grand Blueprint
Гром победы
Heimatkunde
Language updates
Metrology
Natural law = Sharia law
New toys
Skill-estate
Switchover

Powered by Blogger