Monday, 1 October 2012
Autumn reds and yellows
Most trees are still green but the odd patch of bramble, elder and dogwood is beginning to turn.
The framework of most leaves is brown and they only look green because they are full of chlorophyll. The chlorophyll is such a strong colour that it masks the yellow xanthophyll and orange beta-caroteine, which are actually there all through the summer but hidden. So when the leaves stop producing chlorophyll at the end of the growing season, these yellow and orange colours show through.
The red and purple colours, though, are caused by the breakdown of sugars producing pigments called anthocyanins. This occurs most when sunny days are followed by cold nights.