sclerenchyma/prosenchyma

Bob Vickery vickery at JOLT.MPX.COM.AU
Mon May 5 00:27:06 EST 1997


On 2 May, Rod Savage wrote:


>No, I was not assuming that sclerenchyma is the name of a cell type.  I
>said that sclerenchyma conveys the concept of secondary-walled and
>lignified cells lacking bordered pits.  For wood anatomists, sclerenchyma
>comprises sclereids and fibres, and both subdivisions have been subdivided
>further into quite a number of cell types.

Can we agree that 'sclerenchyma' is being used as a 'meta cell type'.

>To my knowledge, the term
>`sclerenchyma' as originally conceived was never intended to be used to
>designate either a tissue or any particular cell type, rather as a
>convenient way of distinguishing one class of cells from another, i.e.,
>secondary-walled and lignified cells which are not capable of conducting
>water from another (viz., tracheary elements) which are.

This is an important point. Could you give me a lead (reference etc) to the
original conception of 'sclerenchyma'.  It may take me a couple of months
to follow up as I will be away for a while.

>(This is not to
>say, however, that there are not some tissues, such as the woody coats of
>many seeds, which are made up nearly entirely of sclerenchyma.  The seed
>coat is the tissue, the various kinds of sclerenchyma constituents of the
>tissue.)
>
>I think the same reasoning applies to parenchyma and prosenchyma.  It has
>never been correct to consider any as either a tissue or a cell type.  If
>folks are making that mistake today, should we argue that words that have
>been used properly over two centuries should now be discarded because of
>ignorant misuse, or should we argue that education in the areas of plant
>anatomy and morphology is not being done adequately?
>

The following definition comes from:

Biology
Knox, B., P. Ladiges, B. Evans (Eds)
McGraw-Hill Book Company: Sydney (1994)

Sclerenchyma: Plant tissue that has a support role; cells with thickened
lignified secondary walls that impart rigidity as well as strength;
includes sclereids, branched or more-or-less even-shaped stone cells that
form the hard tissue of fruits and seedcoats and fibres; elongate cells.

Tissues: Groups of similar, differentiated cells and associated
extracellular matrix, which, together carry out a particular function.

These definitions are similar, as far as I remember, to those in lots of
other text-books.

An older definition:

Willis, J. C.
A Dictionary of the Flowering Plants and Ferns
Cambridge UP: Cambridge (1957)
sclerenchyma: tissue with thick hard walls.

I agree with Rod that these definitions of 'sclerenchyma' are useless since
cases of pure simple sclerenchyma tissue are limited to endocarps and seed
coats.  However, these definitions are in the text books.  I should have
qualified my plea to abolish 'sclerenchyma' by adding 'from the text books
and undergraduate teaching'.

Cheers

Bob Vickery
bob at acsusun.acsu.unsw.edu.au
vickery at mpx.com.au





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