The smell of freshly cut grass brings to mind summer vacation and picnics in the park - pleasant
associations, at least for us. For plants, that same scent is a harbinger of serious
danger.
When a plant is injured - say, by the spinning blades of a lawnmower or a very hungry caterpillar,
pungent chemicals pour out of the wounds, waft into the air and stick in our noses - and
also, to the leaves and stems of nearby plants. Over many generations, eavesdropping plants
have evolved to interpret each different combination of compounds as the signature of a specific
imminent threat. The scent that corresponds to "caterpillar," for example, prompts plants
like tomato and tobacco to churn out bitter toxins in their leaves -- making them yucky
.
Plants can actively communicate, too. Some -- like corn and cotton -- can summon other
animals as defenders: they emit bouquets of chemical compounds that attract parasitic
wasps, which inject their eggs into the nutritiously plump caterpillars so the larvae can eat them
from the inside out. Teamwork!
Plants gossip below ground as well. If you seal the tops of tomato plants in airtight
plastic bags and expose one of them to a harmful leaf disease, the healthy plants will detect
their neighbors' illness and begin making antibiotic compounds. We don't know exactly
how this communication happens, but it's probably through the extensive network of beneficial
fungi that help plant roots absorb and share water and nutrients
However, plants can also use what they learn about their neighbors for nefarious purposes.
Parasitic dodder vines sniff out and steer towards their preferred hosts instead of flailing
around blindly. Another vine somehow grows leaves of different shapes and sizes to match
those of the tree or shrub it's climbing on, using its host for both support and camouflage.
Whatever the purpose - self defense, parasitism or mimicry - plants have been chatting and
eavesdropping in complex social networks since long before Facebook, texting or even -- beep.
If anything, we took a leaf from their book.