BEN # 122

Adolf Ceska aceska at CUE.BC.CA
Sat Dec 16 10:28:53 EST 1995


                                                   
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No. 122                              December 16, 1995

aceska at freenet.victoria.bc.ca        Victoria, B.C.
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 Dr. A. Ceska, P.O.Box 8546, Victoria, B.C. Canada V8W 3S2
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IN SEARCH OF THE FERN SEED (PART 3 OF 3)
From: "Robbin C. Moran" <biobrm at aau.dk>
  originally published in the Fiddlehead Forum 22: 37-40. 1995

We  smile  at  these questions today, knowing that they are com-
pletely misguided, but they were valid questions to botanists in
the 1700s and early 1800s. It wasn't until 1844  that  Karl  von
Naegeli,  a  German  botanist,  steered questions about the fern
seed in the right direction. By focusing his microscope  on  the
undersurfaces  of  the  prothalli  (the membranes or scales that
Lindsay originally reported), von Naegeli saw  globose  papillae
containing dark, spiral filaments. He noticed that the papillae,
when  wet,  burst  at the tip and released the spiral filaments,
which then began to wiggle and swim away. He knew  that  similar
papillae  and filaments had been found in mosses and liverworts,
where they were called antheridia, in  allusion  to  the  "male"
anther  of  the  flower.  Thus, von Naegeli adopted the name an-
theridia for the papillae he saw on fern  prothalli.  But  where
did the spiral filaments swim to?

This  question  was answered in 1848 by Michael Jerome Leszczyc-
Suminski, a Polish count with a botanical bent.  He  found  that
the  spiral  filaments  swam to another kind of papilla also lo-
cated on  the  undersurface  of  the  prothalli.  This  type  of
papilla, which we now call an archegonium, was flask-shaped with
a long neck and a single, large cell at the base. When the sperm
swam to the archegonium, they wiggled downwards between the neck
cells  and  penetrated  the large basal cell. After penetration,
this cell (now known to  be  an  egg  cell)  developed  into  an
embryonic  fern  with  roots,  stem, and leaves. This baby plant
eventually grew into a mature fern with spore-bearing leaves.

What developed from  Leszczyc-Suminski's  observations  was  the
picture  of fern reproduction still taught today. In a series of
quick nutshells this is it: The spores (fern dust) are  produced
on the undersides of the leaves in sporangia. They are liberated
from the sporangia, land on a suitable substrate, and germinate.
They grow into prothalli that bear the sex organs-archegonia and
antheridia-which   produce  egg  and  sperm,  respectively  (the
prothalli of some ferns produce only one kind of sex organ). The
sperm are released from the antheridia when water is present and
swim to the archegonia and  fertilize  the  egg.  The  resulting
cell,  the zygote, develops into an embryo with stem, roots, and
leaves. This embryo grows by widening  its  stem  and  producing
larger  and  larger leaves until a spore-bearing leaf eventually
appears. At this point the process is complete.

This sequence of events is known  as  the  fern  life  cycle-the
bugbear  of  many  Introductory Botany students. It has two dis-
tinct  phases,  or  generations.  The  first   is   called   the
gametophyte  generation  because  it produces the gametes or sex
cells. The second is called the sporophyte generation because it
produces the spores. The gametophyte consists of the prothallus,
and the sporophyte consists of the "normal" fern plant we  typi-
cally  think  of-the  one  with  roots,  stems, and leaves. Each
generation develops from a single cell: the gametophyte  from  a
spore, the sporophyte from a zygote.

One  point  must  be  made  about these two generations, a point
often dimly understood: The gametophyte is the sexual generation
because it produces the sex cells, egg and sperm.  In  contrast,
the  sporophyte  is  the  asexual generation because it produces
asexual spores; it does not produce sex cells. Remember this the
next time you spot a leafy fern luxuriating in  the  wild.  What
you  are  looking  at is an asexual being, one that does not and
cannot engage in sex. This point is difficult to  grasp  because
we  tend to equate, erroneously, our own bodies with that of the
fern sporophyte. But unlike plants,  humans  and  other  animals
produce  their gametes directly by meiosis; we have no interven-
ing  gametophytic  (sexual)  stage  that  produces  gametes   by
mitosis.

But  to  return  to  the fern-seed. Botanists today realize that
spores and seeds are completely different structurally. A  spore
consists  of  a  single cell and contains no preformed embryonic
parts. In contrast, a seed (typically) consists of  hundreds  or
thousands  of cells and contains stored food (the endosperm) and
an embryo. Moreover, spores and seeds differ in what  they  give
rise  to.  A  fern  spore  gives  rise  to the prothallus of the
gametophyte generation; a seed, to the baby  plant  of  the  new
sporophyte generation.

These  differences  between  spores and seeds seem so great that
most of us are astonished when we  learn  that  early  botanists
once  seriously  considered spores were seeds. But our astonish-
ment is only proof that botany has progressed. Nowadays,  it  is
the belief in the fern seed that walks invisible.

Selected References and Notes.

The  history  of  ideas  about sexual reproduction in plants and
animals, especially how it reflects prevailing social  attitudes
about  sex,  is  treated by John Farley, Gametes & Spores, Ideas
about  Sexual  Reproduction,  1750-1914  (Baltimore:  The  Johns
Hopkins University Press, 1982).

John  Lindsay described his observations on fern reproduction in
"Account of the Germination and Raising of Ferns from the Seed,"
Transactions of the Linnean Society 2: 93-100 (1794).

The  life  of  Leszczyc-Suminski  is  documented  by  Cezary  W.
Domanski  in  "M.J.  Leszczyc-Suminski  (1820-1898),  an Unknown
Botanist-Discoverer," Fiddlehead Forum 20: 11-15 (1993).

Author's address: Dr. Robbin  C.  Moran,  Dept. of  Systematical
                  Botany, University of Aarhus, Denmark


UNIVERSITY OF BRITISH COLUMBIA HERBARIUM CLOSED FOR FUMIGATION
From: Olivia Lee <ubc at unixg.ubc.ca>

University  of British Columbia Herbarium (UBC), Vancouver, B.C.
will be closed for fumigation from December 18, 1995 to  January
2, 1996.


NEW RECORDS OF LICHENS FROM THE QUEEN CHARLOTTE ISLANDS
Brodo,  Irwin  M.  1995.  Lichens and lichenicolous fungi of the
      Queen Charlotte  Islands,  British  Columbia,  Canada.  1.
      Introduction  and  new  records for B.C., Canada and North
      America. Mycotaxon 56: 136-173.

Abstract. The Queen Charlotte Islands lie off the west coast  of
North  America,  and  are  characterized  by  a strongly oceanic
climate, coniferous rain forest and rocky  shores,  with  a  low
mountainous  region raising to 1100 m. Its lichen flora is abun-
dant and diverse,  with  numerous  disjunctions  and  new  taxa.
Fifty-four crustose lichens and lichenicolous fungi are reported
as  new  for British Columbia, among them six are new to Canada,
and 18 are new to the North American flora. The new  combination
Porpidia ochrolemma (Vain.) Brodo & R. Sant. is made.

[The  most interesting reports: Lecidea crassilabra - previously
known only from Australia and New Zealand; Pyrenopsis  tasmanica
- previously known from Tasmania and New Zealand.- AC]

oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo
HAVE  A NICE HOLIDAY SEASON AND ALL THE BEST IN 1996! - A. CESKA
oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo

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