Re:Tropica site and Jave fern black spots

Tropica now has an article available at their site about air and water
movements in aquatic plants.  I highly recommend it to everyone on this
list. It can be located at   http://www.tropica.dk/aqh1.htm

>From: Jeff & Denise Dietsch <dietsch at voicenet_com>
>Date: Wed, 14 Aug 1996 22:57:34 -0400
>Subject: Java fern black spot

>Hi all,
>       At the risk of seeming pushy I am reposting my question from a few
>nights ago.  I am concerned for my Java fern and hope someone could assist
>me.  I hope the original post was just missed.  TIA
...................rest snipped.................

The next digest will probably be inundated with info and advice about Jave
ferns better than this, but, based on my limited experience with Java
ferns, here is what I think:

The black areas on the older leaves are said to be a result of nutrient
deficiency, but it is hard to tell which nutrient. I doubt that CO2
fertilization could cause the development of the black areas.   I see
development of the black areas a lot in floating Java ferns, but the ferns
seem to grow better and have much fewer black areas if they can actually
get their roots into gravel.  I have not tried to grow them on driftwood or
rocks, but people claim that they can attach their roots like ivy.  It
would be interesting to know if their ability to get nutrients is improved
when they get themselves attached.  I always see a clear area at the
growing tip of a new leaf.  That is natural and normal.  It is caused by
the absence of any air between the upper and lower epidermis of the leaf.
I have not seen clear areas form in older leaves.  If the older leaf gets a
black area that then turns clear, what is probably happening is that the
tissue dies and turns black, then much of the dead tissue sloughs off,
leaving just a clear epidermal layer.

Under very poor lighting conditions, Java fern can revert to a form that
resembles the gametophyte form.  Ferns have an alternation of generations,
the sporophyte and gametophyte generations.  In the usual fern life cycle,
the sporophyte is the large plant with leaves and roots.  Its cells are
diploid, that is, they have two sets of chromosomes.  On their leaves they
have places where meiosis (reduction division) takes place, producing
haploid cells that become spores.  These spores are released, germinate,
and grow into the haploid gametophyte plant, whose cells have only one set
of chromosomes. The gametophyte is a small flattened plant that has no true
leaves, stems, or roots.  It is a thin, translucent piece of tissue, that
has no air-filled spongy tissue between the upper and lower epidermis.
Instead of roots, it has tiny, hair-like rhizoids like those produced by
moss.  Usually, one never notices fern gametophytes, because they are so
samll.  The gametophyte produces---guess what---gametes, eggs and sperm.
The egg is retained in a little cup of tissue, and is fertilized by a sperm
to produce a diploid cell that grows into the sporophyte.  While
developing, the sporophyte is nourished by the gametophyte, but it soon
develops a leaf and a root, and then starts making its own food.  Soon the
growing sporophyte obliterates its tiny gametophyte "parent".  As I started
to say at the beginning of this paragraph, the Java fern sporophyte can,
under very poor lighting conditions or sometimes when nutrients are in poor
supply, revert to a thin green ribbon with only rhizoids that resembles the
gametophyte.  When light or nutrient supply is improved, it starts
producing true leaves and roots, again.

Paul Krombholz                  Tougaloo College, Tougaloo, MS  39174
In steamy Mississippi.