Garden flowers have a sense of smell? I don't think so. The vegetables growing in my backyard have an aversion to being touched? Surely not. Trees remember the weather? You're kidding. So how does a cherry tree "know" when to flower? Or is it programmed by evolution to switch on flowers in spring?
Do not underestimate plants. On a genetic level plants are more complex than many of the animals that share our planet. Plants have the ability to sense what is going on in the outside world and to share that information among flower, stem, leaf and root. The flower may sense the sun's direction, but it's the stem that must twist in response.
Plants can feel. A burr cucumber vine can detect and respond to a weight of .25 grams. If humans, who can barely detect two grams, possessed the same level of sensitivity, a lover's kiss would resemble a slap in the face. The Venus flytrap feels its prey; one touch and snap! The cause is a chemical reaction that is triggered by two hairs on the inside surface when touched. The hairs can differentiate between the touch of a raindrop and that of an edible fly. There is also the Mimosa plant whose frilly leaves momentarily wilt when touched. The Mimosa uses the same chemicals for neural communication as humans.
Plants can smell. A hard avocado placed in a brown bag with a ripe banana will ripen because the avocado "smells" the ripe fruit's chemicals. This has the ecological advantage of ensuring all the fruits on the tree ripen together. A full display of ripe fruits guarantees a 'ready -to - eat" market for foraging animals, which then disperse the seeds as they go about their daily business.
Plants also sense gravity. Scatter corn kernels over the soil and shoots grow up and roots down. Aerial roots of a banyan tree always grow down, even though they start several feet up in the air. Trees can detect not only insect damage to their neighbors but even the presence of torn leaves. They respond by releasing self-protective chemicals to make their own leaves less palatable.
We pay too little attention to the sophisticated sensory machinery in flowers and trees. On a broad scale, we share biology not only with chimps and dogs but also with begonias and sequoias. So next time you are out in the garden ask yourself: Can that tree see me? Will that vine know where the nearest support is? Does the flower feel the bumble bee? Maybe it's time, as Joni Mitchell sang at Woodstock, "to get ourselves back to the garden" and take a closer look at the plants.
Responding to gravity, the aerial roots of a banyan tree knows up from down.
Trees warn each other of imminent leaf-eating-insect attack.
A sunflower can sense a change in their environments
(gravity, light or smell) and bend in response.
Mimosa is native to South and Central America but is now grown world-wide as an ornamental because of its fascinating moving leaves.
