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) 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 'anti-oxidants' which the 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 are often scarlet. The seed tissue still protected by the seed coat was in contrast pale…. And then the colours of Autumn; another story.