Specificity of Categories: tissue vs organ

E.Kinsman E.Kinsman at roehampton.ac.uk
Wed Oct 27 11:01:59 EST 1999

Tobias Baskin wrote

> 	Sorry to be a pedant, but could the distinction between organ
> and tissue please be maintained? Roots, sepals, leaves, etc, are
> organs; epidermis, xylem, sclerenchyma, etc, are tissues. This is a
> very useful distinction and ought to be preserved.

I don't entirely agree.

Firstly, roots (etc) are organs until they are ground up in the lab, when
they become root tissue, etc!

Secondly, sclerenchyma is not a tissue type, as such, but a
descriptor for a cell type based on its cell wall characteristics.  A
cell is sclerenchymatous if its wall is secondarily thickened.  Thus,
the xylem consists primarily (but not entirely) of sclerenchyma
cells.  Co-ordinated differentiation may give rise to
sclerenchymatous tissue, but sclerenchyma cells may also
occur singly as sclereids.  How then are they to be classified?

I suggest that the plants that we work with themselves defy our
attempts at pedantic classification, because of a lack of absolute
distinction between the various plant organs.  (Where do sepals
finish and petals begin, etc?).

It is important to correct errors where they occur, and to this end
I heartily recommend Katherine Esau's definitive text, 'Plant
Anatomy' (Wiley & Sons, 1953) for those who wish to reaquaint
themselves with the topic.  However, classification which obscures
rather than clarifies is surely to be avoided.

Liz Kinsman

e.kinsman at roehampton.ac.uk

Liz Kinsman
Lecturer in Plant Biology
School of Life Sciences
Whitelands College
Roehampton Institute London
London SW15 3SN

0208 392 3534

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