There you go, learn something new every day!
http://www.telegraph.co.uk/earth/earthn ... utumn.html
Traditional thinking believes that leaves fall as temperatures drop during the autumn, allowing the plant to enter a resting phase and save energy.
But Professor Brian Ford, a scientist, writer and broadcaster, believes leaf drop occurs in order to excrete waste products from the tree.
The president of the Cambridge Society for the Application of Research said: We have long understood the importance of the leaf as the organ of energy capture, through photosynthesis, and of homeostasis, via transpiration.
But the leaf is also an excretophore a means of consigning unwanted wastes to the void. This is why plants all drop leaves.
He found that, shortly before they are shed, levels of potentially harmful components such as tannins and oxalates in leaves increase.
"The levels of heavy metals in abscised leaves are also raised, and they are clearly there to be excreted rather than stored."
Prof Ford argues that leaves do not simply die when plants run low on water, as plants which live in water, such as water lilies, also shed leaves.
He said: "In autumnal landscapes, when plants leaves turn red and brown and are suddenly shed it is important to bear in mind what is happening. The plants are having their annual, well, excretion.
"It does, though, mean that the colouration of leaves in autumn will never seem quite the same again."