Fungi have been called 'Earth's natural internet':

Around 90% of land plants are in mutually-beneficial relationships with fungi. The 19th-century German biologist Albert Bernard Frank coined the word "mycorrhiza" to describe these partnerships, in which the fungus colonises the roots of the plant.

In mycorrhizal associations, plants provide fungi with food in the form of carbohydrates. In exchange, the fungi help the plants suck up water, and provide nutrients like phosphorus and nitrogen, via their mycelia. Since the 1960s, it has been clear that mycorrhizae help individual plants to grow.

Fungal networks also boost their host plants' immune systems. That's because, when a fungus colonises the roots of a plant, it triggers the production of defense-related chemicals. These make later immune system responses quicker and more efficient, a phenomenon called "priming". Simplyplugging in to mycelial networks makes plants more resistant to disease.

But that's not all. We now know that mycorrhizae also connect plants that may be widely separated. Fungus expert Paul Stamets called them "Earth's natural internet" in a 2008 TED talk. He first had the idea in the 1970s when he was studying fungi using an electron microscope. Stamets noticed similarities between mycelia and ARPANET, the US Department of Defense's early version of the internet.

Film fans might be reminded of James Cameron's 2009 blockbuster Avatar. On the forest moon where the movie takes place, all the organisms are connected. They can communicate and collectively manage resources, thanks to "some kind of electrochemical communication between the roots of trees". Back in the real world, it seems there is some truth to this.

Paul Stamets TED talks:

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http://pandawhale.com/post/60289/fungus-network-plays-role-in-plant-communication