GARDENING : Nature Plants the Seeds for Survival Instincts to Take Root and Flourish
Most plants take part in a great lottery, producing hundreds of thousands of seeds and gambling that they will find fertile ground in which to grow--and, in fact, fewer seeds come up winners than people win lotteries.
Seed dispersal is a matter of life and death for plants, and for them to perpetuate their species their seeds must be tough enough to survive severe weather, hungry animals and the odds against being dropped in the right spot.
Plants all over the world employ a variety of inventive schemes to disperse their seeds. A great many of them--from sunflowers to oak trees--simply drop their seeds or nuts in the soil beneath the parent plant where they may germinate if they are not eaten first.
Being a favorite food of squirrels is not necessarily anti-survival for oaks, hickories and walnuts. The squirrels may actually become gardeners when they forget about nuts they buried. Blue jays may plant sunflowers by caching them in fertile soil.
Some plants literally toss their seeds to the wind. From dandelions to cottonwoods, these plants form little parachutes on each seed, which the wind carries away to new areas. Heavier seeds, like those on maples and ashes, grow beautiful sets of wings called “samaras,†that twirl the seeds as they drop from the trees, slowing their descent and allowing them to ride the wind.
Pines and other conifers release winged seeds from dried cones. The tumbleweed uses the wind to roll broken-off plants across the countryside, depositing seeds as they turn.
Other plants eject their seeds in a kind of explosion. The jewelweed, for example, grows its seed pods in such a way that when they are mature the slightest touch of the plant’s tip will cause the pod to “explode,†hurling seeds up to six feet away.
The witch hazel shoots its seeds even farther--20 to 30 feet--before falling to the ground.
Other plants depend on animals to transport their seeds to a new location. Among them are fruits--cherries and berries, for example--whose fruits contain seeds that are eaten by bears, raccoons and birds, later to be deposited in their droppings some distance away.
The same thing happens when birds eat the seeds of poison ivy, ragweed and pokeberry. That’s why so many of these plants are found growing next to fences and fence posts where the birds perched.
Mistletoe, a parasite on trees, depends on birds to eat its berries and then wipe their bills on tree branches to remove the sticky substance that contains seeds, planting the seeds on the tree branch.
