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  Another attempt at contractile roots
From: George Tinsley <gtinsley at netside.net> on 1997.09.10 at 03:57:04(1209)
To put the contractile roots issue into layman's terms, here's my
student-minded effort. First check out Krzysztof's page with the
picture of the roots coming out of the tuber.

The roots, which first grow out in length as the ones in KK's picture,
have to anchor this big old leaf by themselves so what they do is grow
in length to grab deeper into the soil. Then a portion of the roots
contract a few millimeters to securely anchor the weight of the leaf
above them. The roots grow in length, then contract enough to
accomplish what they have to do, so the plant should always be anchored
as much as it needs to be. The contraction occurs when cells in the
cortex of the root expand sideways and achieve the "accordion look."
The entire length of the root doesn't contract, though, so you'll see
the bellows in only part of it, probably near the tuber itself. When
the outer layer of the tuber rots away, the plant should adjust itself
continuously as it needs to because the extra space isn't just created
in a few minutes or a day, it takes a while. When the leaf collapses,
the tuber doesn't have any reason to go down any farther or fall into a
hole because the roots should have had it anchored down as tightly as it
needed to be.

If the tuber isn't dug up, it starts the process again the following
growing season and the new roots anchor it even further as the weight of
the leaf requires it. If anyone has anything else to add or correct,
please feel free since there are far more knowledgable botany-types on
this list.

George Tinsley

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