Where It's Needed
One of the most interesting things to do when you meet a new kind of blossom is to figure out what its "pollination mechanism" is -- how does pollen get from another blossom to this other?
For example, once in Mexico while watching a hummingbird pollinating a Salvia flower I noticed something interesting. When the bird inserted its beak into the flower, the flower's male stamens bent down and dusted pollen atop of the bird's beak and forehead! When the hummingbird left, I opened up a flower to see how the stamens had been able to move. As the drawing at the top of this page shows, each stamen's filament bear a little pivot about midway its length. The stamen is almost like a seesaw. When the backend of the seesaw is nudged by the bill being inserted, the front end with the pollen-bearing anther swivels downward, dousing the bird with pollen. When the bird visits the next flower, that flower's female style, with the stigma at its end, is held just beyond the top petal and thus will be the first part of the flower to touch the bird, and will receive the pollen from the last flower. Can you see how it all works?
If you have blossoming Scarlet Sage at your place, you should open a blossom and see how its stamens are hinged a little like seesaws, as shown in the drawing at the right. When a bee moves beneath the seesaw and her head pushes up the seesaw's back side, the filaments front end with the anthers attached moves down, dousing the bee with pollen. The Salvia mentioned above and Scarlet Sage are in the same genus, the genus Salvia, so it's not surprising that they would have similar workings inside them.
When you try to figure out who or what is pollinating the blossom before you, pay special attention to these features:
Let's review some parts of a typical flower using the Japanese Honeysuckle flower at the right.
In that picture, over at the right, the slender, horizontal thing is the style, and the small, roundish item at the far right, almost touching the picture's edge, is the stigma. The items that curve downward then back up are stamens.
Now visualize a pollinator buzzing into the flower, gathering some energy-rich nectar, then flying away doused with pollen. When you see such a thing you are witnessing a pollinator in the act of pollination -- even though all the pollinator wants is the nectar. Pollination is the act of depositing pollen onto a flower's stigma.
Once a flower has been pollinated and has pollen on its stigma, a pollen grain germinates, sends down a rootlike tube through the flower's style, and the male sex germ migrates from the grain through the tube to an ovule in the ovary, where the female sex germ resides. When genetic information in the male and female sex germs combine, fertilization takes place.
There are many animal pollinating agents other than flying insects. For example, some blossoms, such as those of phlox, possess throats so narrow that many pollinating insects can't enter. Often the pollinators of such flowers are moths or butterflies equipped with very slender, straw-like proboscises, or perhaps hummingbirds, which possess long, slender beaks.
Some flowers stink, so they attract flies or beetles who visit, expecting to find carrion or dung. When the frustrated insects fly away, they carry the stinking flower's pollen with them, perhaps to another blossom smelling the same way.
One of the most common pollinators is not a living thing at all, but rather the wind. Wind-pollinated plants tend to produce prodigious quantities of pollen, and their stigmas are often large and feathery, to increase the stigma's surface area, and the chance of windblown pollen landing there. Grasses are typically wind pollinated, as hay-fever sufferers can attest.
Above you see a cross-section of a flower a Yellow Jessamine vine, Gelsemium sempervirens. Notice how the ovary has such a long style, with its two-lobed stigma held high above the corolla. Pollen-producing stamens are attached to the corolla wall deep inside the blossom's tube. Having the stigma held so high above the stamens helps prevent pollen from the stamens from landing on the blossom's own stigma.
Sometimes the female stigma projects just a tiny distance beyond the male stamens. However, that tiny distance serves its purpose, keeping self pollination from taking place. The picture at the left shows a cut-away view of a Paulownia flower, which is just such a flower.
Another common strategy to avoid self pollination is to have the male stamens mature at one time, and the female pistil at another time.
Sometimes nature makes absolutely sure that no self pollination occurs by placing male flowers on one plant, and female flowers on another, as with the Red Maple, Acer rubrum, shown at the right. In that picture, the branch at the left female stigmas emerging while on the right you can see clusters of emerging stamens. To make things more complex, sometimes you'll see on the same Red Maple one branch that is entirely one sex, but other branches that are entirely of the other sex!
Here are some profoundly important points to keep in mind when thinking about pollination:
Therefore: It's clear that the welfare of pollinators is critically important to the welfare of all the Earth's terrestrial ecosystems.
Yet, today, many pollinators are endangered, especially because of habitat destruction and the use of chemical pesticides.