Nature has several interesting ways of bringing about pollination. In
the corn, willow, and pine the pollen is picked up by the wind and
carried away. Much of it is lost, but some reaches the stigmas, or
receptive parts, of other corn, willow, or pine flowers. This is a very
wasteful method, and all plants using it must provide much pollen.
Many plants employ a much better method. They have learned how to make
insects bear their pollen. In plants of this type the parts of the
blossom are so shaped and so placed as to deposit pollen from the stamen
on the insect and to receive pollen from the insect on the stigmas.
When you see the clumsy bumblebee clambering over and pushing his way
into a clover blossom, you may be sure that he is getting well dusted
with pollen and that the next blossom which he visits will secure a full
share on its stigmas.
When flowers fit themselves to be pollinated by insects they can no
longer use the wind and are helpless if insects do not visit them. They
therefore cunningly plan two ways to invite the visits of insects.
First, they provide a sweet nectar as a repast for the insect visitor.
The nectar is a sugary solution found in the bottom of the flower and is
used by the visitor as food or to make honey. Second, flowers advertise
to let each insect know that they have something for it. The advertising
is done either by showy colors or by perfume. Insects have wonderful
powers of smell. When you see showy flowers or smell fragrant ones, you
will know that such flowers are advertising the presence either of
nectar or of pollen (to make beebread) and that such flowers depend on
insects for pollination.
A season of heavy, cold rains during blossoming-time may often injure
the fruit crop by preventing insects from carrying pollen from flower to
flower. You now also understand why plants often fail to produce seeds
indoors. Since they are shut in, they cannot receive proper insect
visits. Plants such as tomatoes or other garden fruits dependent upon
insect pollination must, if raised in the greenhouse where insects
cannot visit them, be pollinated by hand.
Exclude insect visitors from some flower or flower cluster, for
example, clover, by covering with a paper bag, and see whether the
flower can produce seeds that are capable of growing. Compare as to
number and vitality the seeds of such a flower with those of an
uncovered flower. Observe insects closely. Do you ever find pollen
on them? What kinds of insects visit the clover? the cowpea? the
sourwood? the flax? Is wheat pollinated by insects or by the wind
or by some other means? Do bees fly in rainy weather? How will a
long rainy season at blossoming-time affect the apple crop? Why?
Should bees be kept in an orchard? Why?
Next: Crosses Hybrids And Cross-pollination
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