Re: Fasciation (was Taro Anomaly (Pictures)

Richard Dufresne wrote:
> 
> At 10:09 PM 9/5/2002 -0700, you wrote:
> 
> >
> >Side view showing "conjoining"
> >
> >Anyway, there you have it. What the pics don't show is
> >that the stem is much thicker than usual, and it looks
> >like there are spots where new leaves can emerge on
> >either side of the stem. It's like the terminal bud
> >developed two leaves at the same time and they fused.
> 
> I've seen various instances of fastigation (from Latin 'sloping to a point')
> where multiple branches emerge from a node and have connective tissue
> between them for  part of the distance.  This feature reminds me of sci-fi
> modified humans with webbing between their fingers as if they were modified
> to live underwater.
 
Webbed digits on humans is not confined to Sci-Fi stories. When young I
was at boarding school with a a pair of sisters (not twins) who both had
extensive webbing between their toes. The younger one was a pretty good
athlete, but not i think particularly interested in swimming.

> 
> I once had an Aloe vera that showed a spectacular example of this.  Most of
> the pot was taken over by a wavy ridge of short conjoined stems.  It became
> my favorite stock plant, since I could break off the short stems and root
> them nicely.

I have occasionally seen fasciation in my garden. Once I had a Lilium
formosum produce almost spectacular ribbon of stem more than an inch
wide and several feet high with attenuated flowers up both sides and I
have had a similar effect with an heirloom cucumber, where the wide vine
grew several feet high, but though it flowered copiously I don't think
it set any successful fruits.
The lily reverted to its normal grwoth in the following year and I think
this can quite often happen to perennials which show such anomalies, but
on some they do indeed recur and the plant may need to be discarded.
>
> 
> I seem to remember that this effect is at least sometimes caused by a
> bacterial infection.  I once had a Salvia purpurea that developed an
> apparent callus growth where the lowest nodes should have been.  Instead of
> one or a few main stems, there were a plethora of small stems with stunted
> leaves.  Many of these would die off, leaving a few more normal stems to
> grow.  The effect persisted with plants made from these cuttings, and I
> eventually replaced my stock.

Some examples are certainly pathologic and usually ascribed to bacterial
action, but many seem to be produce withut any such agent and are
probably just a form of genetical mis-coding, which is of course usually
known as a mutation.

The many miniature conifers beloved by Alpine gardeners are nearly all
derived from witches brooms (another manifestation of fasciation) which
have originally grown on full-sized trees. They will normally stay in
character indefinitely, but need to be watched as occasionally the
dwarfing effect wears off and a normal shoot of the parent tree will
grow out and swamp the "tiny" if not quickly removed.

If the fasciated section of the parent tree is completely removed normal
growth will usually then develop from the cut.

While I suspect many if not all of the conifer abberations are simply
mutations and not pathological in origin, I am not so sure about those
which occur quite commonly here on certain individuals of Silver Birch
and the Tokyo Cherry (Prunus yedonesis), and are most unattractive and
disfiguring.. 
> 
> Perhaps there are biological agents producing compounds like gibberelic acid
> that cause these effects.  Comments by plant pathologists will be welcome.

Unfortunately, if this aspect (the basic mechanism of broom formation)
has been investigated, I have not myself been so far able to find any
trace of the details. If I manage to come up with anything useful later
I will let you know.

Moira

-- 
Tony & Moira Ryan,
Wainuiomata, North Island, NZ.     Pictures of our garden at:-
http://mywebpages.comcast.net/cherie1/Garden/TonyandMoira/index.htm
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