Plant Behavior and Nonliving Things
Some parts of a plant grow up and some parts grow down. The things a
plant does are called its behavior. When a seed starts to grow, a tiny
root comes out first. And somehow it always grows in the right direction. It
seems to know where “down” is. A plant knows which way is down because of
the pull of the earth on certain chemicals in the root. These chemicals
help the root grow down. Plant stems play tug-of-war with the earth. The earth
pulls roots toward it. It also pulls stems toward it. But stems grow up, not
down. Growth chemicals in the stems help the stems pull harder. The stems win
the tug-of-war over the earth’s pull. Green plants need light to grow. Some
plants can grow so they get the amount of light they need. Suppose a plant were
getting light from only one side. The stem might then grow so that its leaves
would be turned toward the light. The stem of many green plants can do this
because of growth chemicals in the stem.
plants get water from the soil. The roots help the plant get the water it needs.
But suppose the soil right around a plant is very dry. If there is water
somewhere nearby, a little bit of the water may reach the root. That will cause
the root to grow toward the place where more water can be found.
“breathe” out water vapor. Plants have openings on their leaves for doing
this. But when the air is very dry, the plants give off very little water vapor.
The dry air causes the openings on the leaves to close up.
Plant Behavior and Living Things
Deserts get very little rain. Some desert plants have many roots. These
roots help them get as much water as possible. But if other plants get too
close, there may not be enough water for all of them. One desert plant, the creosote
bush, takes care of this. The roots of this bush give off a poison. Suppose
another plant, even a young creosote bush, started to grow near an older
creosote bush. The poison from the older plant would kill off the younger plant.
This takes care of the problem of crowding for the creosote bush!
plants use poisons to protect themselves from hungry animals. Poison ivy makes a
poison that bothers animals if they rub against it. Animals soon learn to stay
away from poison ivy.
plants have a different way of protecting themselves. A certain grass is found
where animals graze. If animals get near this grass, the grass droops. Then the
grass doesn’t look good to eat. The animals may pass it up. Another plant, the
mimosa, also droops at times. As soon as someone touches it, it draws its
leaves close together.
plants eat animals such as ants and flies. These plants can grow in very poor
soil. The soil does not have to supply all the minerals these plants need. These
plants get some of the minerals they need from the animals they eat. One plant,
the sundew, has sticky hairs all over its leaves. When a fly lands on a leaf,
the fly gets stuck. Nearby hairs bend toward the fly. More sticky stuff pours
over the fly. The fly cannot get away. Juices from the plant turn the fly’s
body into a “soup.” The plant takes in this “soup” through its leaves.
Another kind of animal-eating plant is the pitcher plant. Certain leaves of the
pitcher plant catch rainwater. Ants or other small animals may crawl into these
leaves looking for nectar. They often slip and fall into the water. That’s the
end of the ants! Juices from the plant soon digest them. Another plant also eats
animals. It is called the Venus’s-flytrap. When a fly lands on a leaf of this
plant, the leaf closes up quickly. The fly cannot escape. Soon it is digested.
plants take care of themselves in still another way. They have weapons. The
cactus has spines all over its stems. Spines help the kapok tree, too. Sometimes
birds have mistletoe seeds stuck to their feathers. They rub the seeds onto some
plants. The mistletoe then starts to grow on these plants. But the mistletoe can
be harmful to these plants. It steals the water these plants take in from the
soil. But, because of the kapok’s spines, birds don’t rub mistletoe seeds
off on the kapok tree. This protects the kapok tree from mistletoe.
“friends.” At certain times some plants have flowers on them. Some
flowers have bright colors. The colors attract insects like bees. The flowers
also make sweet nectar that many insects like to drink. In return, you might say
the insects do a favor for the flowers. The insects carry pollen from a flower
to another flower of the same kind. Pollen is the white or yellow dust made by
certain parts of flowers. Pollen is needed by the flowers to make their seeds.
One plant, the yucca plant, has a special friend. It is the yucca moth.
The yucca flower opens up just once. It opens one evening. It stays open all
that night. The next morning it closes, never to open again. Because it stays
open only at night, day insects, like bees and butterflies, cannot carry its
pollen. But the yucca moth flies at night. At night the yucca flower, which is
white, shines in the moonlight. It also gives off a sweet smell. These things
attract the yucca moth. The yucca moth then carries pollen from one yucca flower
to another. At the same time, the yucca moth lays its eggs in the yucca flower.
often, insects eat plants. People often spray the plants with insecticides.
Insecticides kill the insects. But they often kill other living things, like
birds and mammals. Sometimes the insecticides stay on the plants. They can get
into the vegetables you eat. There is a better way to keep insects and worms
away from some plants. Certain plants can be used to chase away insects and
worms from other plants. Marigold plants make a poison. Because of this poison,
insects and worms leave marigolds alone. This poison is also helpful to
rosebushes growing near marigolds. The roots of rosebushes are often destroyed
by roundworms. But the poison from the marigolds chases the roundworms away.
Rosebushes which grow near marigolds are healthy. Rosebushes also grow better
when garlic plants are near. The garlic keeps beetles away from the roses.
Asparagus plants keep worms away from tomatoes. Onion plants keep carrot flies
away from carrots.