

Underground signals warn neighbouring plants of aphid attack - smaili
http://onlinelibrary.wiley.com/doi/10.1111/ele.12115/abstract;jsessionid=43E51315EFE948C1A0C3617E273ACFDD.d01t01

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a_bonobo
There are many known ways in which plants communicate (if you want to call
that communication):

\- ethylene is a gas, but also a plant hormone that causes (among others)
ripening of fruits. So if you got a field of apple-trees, when the first
tree's fruits starts to ripen and release ethylene there's a chain reaction
where other trees detect the gas and causes the other trees to ripen their own
fruits (and release more ethylene). This is used in the industry so you can
transport unripe fruits and ripen them later with ethylene.

\- Trees of Heaven produce hormones that they use to tell other plants to stop
growing, so to speak [1]

\- When lima beans are attacked by herbivores or parasites, they release
gaseous substances that warn other plants, who then in turn upregulate their
defences [2]

There are many, many, many more examples, it's awesome :)

[1] <https://en.wikipedia.org/wiki/Ailanthus_altissima#Ecology>

[2] <http://www.mpg.de/942876/W001_Biology-Medicine_060_065.pdf>

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kevinwuhoo
IMHO what's even cooler is a type of plant defense where they cooperate with
other organisms to fend off herbivores. Some plants are known to emit organic
volatiles which attracts predators of these feeding herbivores.

For example moth larvae ( _Manduca sexta_ ) feeds on tobacco ( _Nicotiana
attenuata_ ) plants. The tobacco plant releases leaf volatiles which float
through the air to attract a predator (a big eyed bug, _Geocoris_ ) to feed on
the larvae. [1]

[1]: <http://www.plasmyd.com/doi/10.1126/science.1191634>

