Re: How Does a VFT Shut?

From: John Green (
Date: Fri Sep 03 1999 - 08:38:05 PDT

Date: Fri, 03 Sep 1999 09:38:05 -0600
From: "John Green" <>
Message-Id: <aabcdefg3132$foo@default>
Subject: Re: How Does a VFT Shut?

>>Concerning the VFT, the
>>article says that after the trigger hairs have been set off, the
>>plant pumps water rapidly around the leaves partially closing them
>>by hydraulics. They then fully close by the cells on the outside
>>multiplying. "The trap actually grows shut" quotes Paul. My
>>understanding had been that the trapping of the insect is caused by
>>rapid cell growth, not hydraulics. Which is right?

I'm an accountant, not a botanist, so I don't know if this is correct
or not, but no one responed yet on this. My understanding was that the
initial closing of the trap was caused by turgor (sp?) pressure. As I
understand it, turgor pressure is the pressure in the plant from the
water in it's tissues that holds the leaves erect. For example, the
little bean seedlings my son planted in a styrofoam cup haven't been
watered recently (in other words, they're de-hydrated) and they're
beginning to wilt. So, my understanding was that this pressure in the
leaves, and also that the two halves of the trap are convexly curved
away from the midrib, that causes it to "snap" shut on the insect. I
guess after that, it's been found that the cells on the outside of the
trap multiply rapidly (I don't know what it's called) and cause the trap
to finish closing. In Don Schnell's book "CP of the USA and Canada" he
says that the midrib in the center of the trap doesn't actually move in
the initial "fast" phase of closing, but it's more a matter of the
halves being convex before closing and concave after closing, but the
midrib does appear to move in the later closing phase as the leaf halves
are actually brought together. The only part of this "rapid cell
growth" that I don't understand is it doesn't explain why the halves
press against the insect (IMO). I can understand how it would close the
opening around the edges, but it seems that would only make the trap
halves more concave around the prey, rather than seeming to squeeze it,
or press tight against the insect body. Also, what about the next time
it catches something, as each trap can catch several insects before
dying? Wouldn't all those new cells on the outside of the trap make it
harder to re-open?

So anyway, I don't know about the word "hydraulics" being used by the
magazine, but I guess that's pretty much what it is. Hopefully, someone
with better knowledge can update us on what is believed to cause the
trap to shut.

John Green
Salt Lake City, Utah

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