When Plants Cry
When I was about 9 or 10, I read a book of short horror stories. In one of the stories, a man developed a machine that allowed him to hear out of the range of normal hearing limits for humans. He took the machine outside to test it out and kept hearing shrieking at different intervals. When he looked around he realized that his neighbor was pruning roses, and he heard a cry each time his neighbor clipped a rose.
To determine whether plants really were making the sounds, he took an axe out to a park and found a big, old tree. He swung the axe into the tree and the tree let out a long, low moan of anguish and pain. The sound upset the man so much, he called his doctor to come hear the sound. Unfortunately, before the doctor could hear, a branch crashed down and destroyed the machine.
This story has stuck in my mind for years, and I was again reminded of it about a month ago.
I was doing some research on gases released by plants for a client. Plants release different chemicals in gas form – these are the floral scents that allow us to discriminate between a lily, for example, and a rose.
I never gave a lot of thought about plant scents beyond whether I enjoyed them or found them to be noxious (lilies!).
It turns out that instead of just smelling nice (or not), the scents released by plants have a purpose.
Plants undergoing stresses, such as those caused by the environment (for example drought) will give off different scents than plants that are receiving everything they need.
Plants will also release different scents if they are mechanically damaged – think of the nice fresh-cut grass smell that happens after you mow your lawn. Different scents will be released if plants are being attached by insects or fungus.
Some gases are stored in the plants and are immediately released when the plant is damaged (grass cutting) but other scents aren’t made until the plant senses danger and are released hours to days after the plant is attacked.
Why would plants do this?
Some scents act as chemical messengers, an SOS signal that is delivered to other parts of the plant or to neighboring plants. Plants respond to these signals by boosting their own ability to prevent damage by insects or other dangers.
Other gases act as natural pesticides, chasing bugs away. Wintergreen oil is released as a gas by the majority of plants in response to insect attack.
More fascinating however, is the fact that some scents attract other insects that will feed on or repel the insects that are attacking the plant. An extreme form of this is when a plant is eaten by caterpillars, it will release scents that attract a certain type of wasp. The wasps will sting the caterpillars and at the same time deposit their eggs inside the caterpillars. The caterpillars’ growth will be halted and the caterpillars will become incubators for the wasp larvae. It’s a win-win situation for the plants and the wasps!
It’s amazing to me that plants have developed a form of communication using scents. But it is also a little unnerving to think that the smells I enjoy so much could be plants crying for help.
Note: I found the story! It is a story by Roald Dahl called The Sound Machine. The book I read it in was Alfred Hitchcock Presents: Stories for Late at Night.