At 9:02 AM 9/23/96 -0700, jperry at UWC.EDU wrote:
>Stump the anatomist time...
>>I have a block of oak wood (no bark) in front of me that has a very unusual
>pattern within its growth increments. It was given to me with a question of
>why this pattern exists. I'll do the best I can to describe it.
>>Looking at the cross section, *all* the growth increments (and I can count
>16 of them in this block) between two multiseriate rays are displaced in a
>radial direction (toward the pith). The displacement is such that the early
>wood of the displaced increments fall in the late wood of growth increments
>on either side. I'll try to create another way of explaining this:
>>"early" = early wood
>"msr" = multseriate ray
>"late" = late wood
>>Imagine you are following the circumfernce of the growth increments.
>> ... msr early msr early msr late msr early msr early msr ...
> ... msr early msr early msr late msr early msr early msr ...
> ... msr early msr early msr late msr early msr early msr ...
> ... msr early msr early msr late msr early msr early msr ...
> ... msr early msr early msr late msr early msr early msr ...
> ... msr early msr early msr late msr early msr early msr ...
> etc...
>>Note that the late wood is in the displaced growth increment.
>>I can't imagine how the vascular cambium could be so perfectly displaced to
>cause this to happen in *one single* radial file of growth increments.
>>Does anyone know for certain (speculation is fine, but I'm hoping for a
>definitive answer) how this occurs?
Jim,
My speculation: the cambial initial that gave rise to this sector of
secondary xylem has mutated in some gene critical to radial expansion of
the derivatives. Perhaps a microtubule-orienting gene now causes the
extrusion rosettes to migrate only radially in the cell so that all
cellulose microfibrils are oriented around the cells (with respect to
stem). Since cells cannot expand radially, the cambium must simply produce
more cells to stay "synchronized" with the adjacent populations of meristem
cells. There is a theory about pressure-induced cell divisions that might
explain the accelerated production of derivatives in this sector of the
cambial zone to compensate for lack of radial cell expansion. I think Paul
Green was the author on that.
Anyway, it is interesting!
ross
______________________________________________________________
|
Ross Koning | Koning at ecsu.ctstateu.edu
Biology Department | http://koning.ecsu.ctstateu.edu/
Eastern CT State University | Phone: 860-465-5327
Willimantic, CT 06226 USA | Fax: 860-465-5213
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Plant Physiology is Phun!
/\|___/\ //\______COOH NH-CH2-CH=C-CH2OH \/OH
| | | | | | || //\___ \CH3 /\|/\\/\\COOH
\/ \/|\/| \\/ \ / N || N | |
/\ | |__|= NH | || || //\//\
| COOH \\ /\ / O
COOH H2C=CH2 N NH
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