How plants sound the alarm about danger. Just like humans and other animals, plants have hormones. One role of plant hormones is to perceive trouble and then signal to the rest of the plant to respond. A multicenter team is reporting new details about how plants respond to a hormone called jasmonic acid, or jasmonate. The findings could help researchers develop crops that are hardier and more able to withstand assault, especially in an era of rapid climate change. Source 9q.
Plants send signals into the atmosphere to communicate with other plants and with animals: when a plant is attacked by a pathogen or herbivore it releases certain compounds into the air that "Warn" other plants of impending danger, so they can prepare to receive it.
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Isn't that why we have the distinct smell of cut grass? It's that warning chemical.
And what I find even more fascinating is that forests have their own 'communication network', linked through their roots. I could be wrong, but I think you have the 'mother' tree, all of its saplings, a few neighbors, and the resident fungi all tapped into the party line.