单项选择题
| Orchids are unique in having the most
highly developed of all blossoms, in which the usual male and female
reproductive organs are fused in a single structure called the column. The
column is designed so that a single pollination will fertilize hundreds of
thousands, and in some cases millions, of seeds, so microscopic and light that
they are easily carried by the breeze. Surrounding the column are three sepals
and three petals, sometimes easily recognizable as such, often distorted into
gorgeous, weird, but always functional shapes. The most noticeable of the petals
is called the labellum, or lip. It is often dramatically marked as an
unmistakable landing strip to attract the specific insect the orchid has chosen
as its pollinator. To lure their pollinators from afar, orchids use appropriately intriguing shapes, colors, and scents. At least 50 different aromatic compounds have been analyzed in the orchid family, each blended to attract one, or at most a few, species of insects or birds. Some orchids even change their scents to interest different insects at different times. Once the right insect has been attracted, some orchids present all sorts of one-way obstacle courses to make sure it does not leave until pollen has been accurately placed or removed. By such ingenious adaptations to specific pollinators, orchids have avoided the hazards of rampant crossbreeding in the wild, assuring the survival of species as discrete identities. At the same time they have made themselves irresistible to collectors. |