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Colours that protect in spring |
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Monday, 10 March 2008 |
This cameo of colour breaks the muted
shades of grey and green of the winter
woods. On a log is a bright yellow jelly fungus
(Tremella mesenterica) surrounded by
reddened leaves of ivy, and a turquoise green
morsel of lichen, which has fallen from the
tree above. The
consistency of the
fungus is akin to an
ill-solidified lump
of jelly. It has
neither taste nor
smell. In dry
weather, it shrivels
to a tiny mass, but
when it rains it will
expand tenfold.
When the sun
returns, spores are
produced and are
shot a very short
distance so that a
breeze can carry
them away. In the
economy of Nature,
it is a valuable
decomposer of dead
wood.
Does anything
eat it? I detected minute creatures, millipedes
and springtails, grazing the surface, but as far
as I know nothing larger eats it. This jelly
fungus is common throughout the year but
stands out strikingly in winter.
Yellow is the colour of spring (gorse,
primroses, daffodils); is this significant? The
colour comes from chemicals called
carotenoids. Arguably, the carotins in the
flowers and in this fungus are a chemical
protector against too much sunlight. This
pigment acts in the same manner as the ‘antioxidants’
which nutritionists these days urge
us to eat to keep our youthful appearance.
The red colour of the ivy leaves is due to
another group of chemicals, the anthocyanins,
which are also anti-oxidants protecting the
tissues from sunlight. They are themselves
created through the chemistry of sunlight
acting on sugars and proteins in the tissues.
Where one leaf shades another, the red is not
formed. Other factors though must be
involved. The ivy leaves at the top of a tree are
rarely reddened.
The anthocyanin is
only red if the cell
sap is acid. In this
respect it acts like
the litmus of
school chemistry,
changing colour
from red if acid
to green/blue if
alkaline. Ivy leaves
contain much
oxalic acid, which
is why they are
poisonous (as
also with rhubarb
leaves). Ivy berries
also contain
anthocyanins but
are less red and one
supposes less acid.
If you extract in hot
water (plus a little
alcohol) the colour from ivy berries or red
leaves like these, then the liquid which is a
dirty green will turn red if a little white
vinegar is added.
But surely cold is also playing a part in
these colours of the ivy. Young leaves of many
plants in spring are red. It is possible that the
red pigment helps the leaves to resist frost, or
perhaps bright sunlight is more damaging to
cold plant tissue. These leaves on the ground
were most certainly subject to frost, as were
the many acorns in the area. These seeds were
germinating and where the sun shone on the
bare flesh of the acorn they were often scarlet.
The seed tissue still protected by the seed coat
was in contrast pale…. And then the colours
of autumn; another story.
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Downtime 
