mimosa

I've been growing some mimosa seedlings (you might know it as 'shy grass') on my desk for a while now, and the new pinnate leaves have unfurled. I spend a few minutes of each day tormenting the poor leaflets, making them fold up by poking them. It's said that this is a defence mechanism, to hide the leaves from herbivores and generally making them less accessible for munching. I'm not sure if this is the real evolutionary reason, but if I were a sheep, I would definitely be a little taken aback if my lunch started to curl up before I took a bite. At least the birds won't mistake the moving leaves for lunch - worms and caterpillars of such a lucid green tend to be poisonous.