Specificity of Categories: tissue vs organ

Antony Patchett piwy at dna.bio.warwick.ac.uk
Thu Oct 28 10:57:57 EST 1999

> From:          E.Kinsman at roehampton.ac.uk ("E.Kinsman")
> Firstly, roots (etc) are organs until they are ground up in the lab, when
> they become root tissue, etc!

I don't really understand why this argument is occuring, looking at
animals, the liver is an organ, but is then liver tissue when ground
up, and what is the problem saying that certain organs are made up of
certain tissue types? To me your argument is non-sensical (no
offence intended).  Tissue types define the make up of the cells at
one level, and organs define groups of possibly disparate cells in
terms of their gross function at another level. The distinctions
between organs may be less precise in some cases in plants compared
to other organisms, but the terms are not mutually exclusive.

> 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
Antony Patchett Bsc GIBiol
Dept. of Biological Sciences
University of Warwick
Tel: (01203) 523523 ext. 22556
Mobile: 07775 513814
Email: piwy at dna.bio.warwick.ac.uk

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