vickery at JOLT.MPX.COM.AU
Mon Apr 28 09:16:51 EST 1997
David R Hershey wrote most pertinently about some horrors of botanical
>Most botany texts state that all plant cells are either parenchyma,
>collenchyma, or sclerenchyma, but then don't follow through and use
>those terms to identify all the specialized cell types discussed
>later, such as sieve tube element, guard cell, and cork cell (all
This is a great illustration of problems with botanical nomenclature. The
text books that I know define parenchyma, collenchyma and sclerenchyma as
tissues, consistent with their Greek roots. The corresponding cell types
are parenchyma cells, collenchyma cells and sclerenchyma cells.
Sclerenchyma has two types of cell: fibres and sclereids.
There are precious few examples of real sclerenchyma tissue in plants. The
endocarp of drupes is the only example I can think of, being made up of
sclereids. Fibres are mostly found in xylem tissue or in phloem tissue,
not in a separate sclerenchyma tissue. Sclereids commonly occur as
isolated small groups of cells embedded in parenchyma (tissue). What do
students make of xylem parenchyma cells which have rather strong lignified
walls? What about libriform fibres? Are they parenchyma or sclerenchyma
cells? 'Sclerenchyma' should be abolished.
'Parenchyma cell' should also go. I define parenchyma cells as having
living cytoplasm and only a primary wall at maturity. Cells of very
different functions and origins are caught up in this definition, such as
the sieve tube element and guard cell mentioned by David. (It doesn't
include cork cells except for phelloderm). Some xylem parenchyma cells, I
read somewhere, have secondary walls and should not be included by this
definition. We may need to use several more specialised names such as
'storage cell', 'photosynthetic cell' and 'packing cell'.
'Collenchyma' and 'collenchyma cell type' seem to be consistent, thanks be!
bob at acsusun.acsu.unsw.edu.au
vickery at mpx.com.au
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