Plants: Nastier Than You Thought
A fly happens into a fly trap’s sticky leaves, and within seconds the Leaves of Death close over the fly. Who knew a plant could hustle so fast? This rapid plant movement is called haptonasty (from the Greek for nasty happenstance).
I’ve mentioned in another post that in our animal imaginations, plants don’t get credit for being fully alive. Why? Partly, because we think of them as unmoving. However, many plants exhibit rapid movements, like the leaf-closing mentioned above, or the instant collapse of leaflets in the shy Mimosa, or the closing of flowers at night. These “nastic” movements are caused by rapid chemical or pressure changes in the cells.
Nastic movements remind us of the twitchings of our own nervous systems. Add carnivorism to that, and a plant like the Venus fly trap gets elevated to near-animal status. But to really appreciate plant movement, we have to think a little differently. Most plant movements are tropisms, or growth movements. It is an elegant concept: instead of running, creeping, crawling or skedaddling, plants grow toward or away from a stimulus.
One visit to the Hoh Rain Forest in Olympic National Park, Washington, will show you how desperately alive plants are. Witness the epic battle as two Western Red Cedars vie for the nutrient-rich real estate of a nurse log! Avert your eyes from two Douglas Firs fused into a lewd position! See a severed tree come back from the dead, zigzagging toward the light! All this from growth movements.
I used to work on a farm in New York. Lettuce seeds were very stubborn in the summer, but they would have a much higher germination rate if we put the flats in the cool basement. The trick was to remove them from the basement as soon as they broke soil. Otherwise we would end up with 20 flats full of ghostly pale, thin stems, tilting toward the sunny chink in the wall. The legginess would weaken the plants permanently, and they would go to waste.
Our neglected lettuce seedlings still thought they were underground. When a newly germinated shoot is still below ground, it puts all its energy into the elongation of its stem. When it breaks ground, the sensitive phytochrome receptor senses light, and the plant begins “greening.” The stem slows its elongation, the roots begin to develop, the leaves expand and start producing chlorophyll, and the mitochondria develop environmentalist sentiments and strive toward an Energy Star rating.
Plants will not only move in response to light, but also to touch, gravity, and chemical stimuli. In (the awesomely named) thigmomorphogenesis, plants move in response to touch. Like a baby wrapping its hand around a finger, a pea plant will wrap its tendril around a support.
Botanical drama isn’t limited to the Hoh Rain Forest. As we know, plants can’t change location to defend themselves. But they have their sneaky ways. Some plants carry out elaborate sabotage against their enemies. When a corn leaf detects the drool of a munching caterpillar, it sends out a smell that attracts parasitoid wasps, which lay their eggs in caterpillars so the newly-hatched wasp larvae can eat them from the inside out. Talk about underhanded. But plants can’t throw punches. They do everything slowly and cleverly.
Once the word gets out that plants are exciting movers and shakers, maybe a botanical Steve Irwin will emerge. I can see it: a boisterous, khaki-clad outdoorsman wrestles a sedge to the ground while sucking on poison hemlock root. This is gonna be big!