[chidg]

You're right about the language, but the mechanism is real The evolution of gaseous defense hormones in plants is thought to actually benefit the same plant, but has a side effect of 'warning' the plant's neighbours. Because plants don't have a bloodstream, chemical diffusion of messenger molecules throughout a plant is pretty slow. So some plants just use the air around them as a signalling medium, and when they are damaged, release gases into the air which their other leaves can detect. Of course, the gases also affect their neighbours.