Bill Williams bwilliam at oyster.smcm.edu
Sat Dec 18 13:14:24 EST 1993

In article <2etd1i$aes at pinyon.libre.com>
woody at pinyon.libre.com (Woody Harper) writes:

> Is rhubarb really poisonous? I have heard that the leaves are toxic but
> the rest is ok. How would the plant know to keep the two parts seperate?

The leaves contain sharp, hard crystals of oxallic acid called "raphe"
that can damage soft mouth parts, both physically and chemically. The
petioles (the part that's usually eaten) have plenty of oxallic acid,
but fewer raphe.  As to how the plant "knows" to keep the two parts
separate, that's either very simple or virtually unknown, depending on
how you mean the question.  The plant does make very different
chemicals, cell types, and structures in different parts (think of a
potato in comparison with the above-ground plant that makes it), a
process called "differentiation," and it's a very complex process under
intense study by plant biologists of many specializations.

Hmmm... sounds a bit text-book-ish, but then I'm a professor, what do
you expect?
William E. Williams
Department of Biology
St. Mary's College of Maryland

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