Erica's Original Notes It should be understood that pollination is NOT necessarily fertilization; however, it is a miracle how the pollen grain finds the unfertilized ovule; in corn it is 18 inches from the end of the silk to the ovule, and that journey is accomplished within a few hours!
Nectar: made by flowers to encourage airmail delivery of pollen by insects and other pollinators. In 1927 von Frisch did research into the peak hours of nectar output by various flowers, using bees as indicators. Brassicas spp. (mustards) peaked at nine a.m., Centaurea (knapweed) at eleven a.m.; clover and fireweed at one p.m., and viper's bluegloss at three p.m. Try it out for yourself an excuse for lazing around outside in the sun! (See Note 1 below)
Nectaries: sometimes on their own; those of hellebores are really modified petals, and the ones found in fritillarias look like tear drops at the base of the petals.
Tricks: played by flowers in order to get the insects, birds and animals to transport their pollen to another flower in the same family. They sometimes imitate insects to act as a decoy, as in orchids which mimic the female fly. It is all an amazing adaptation when you realize that plants were on earth before the insects!
Robbers: birds and insects which try to steal the nectar by piercing holes in the calyx, so that is the reason for hard or swollen calyces. Teasels protect their nectaries from robber ants by water held in leaf cups.
Cross-pollination: promoted by the varying heights of stigmas and anthers; self-pollination is a last resort, as cross-pollination improves adaptation to environment by increasing genetic diversity.
Signs of fertilization: given by some flowers so as to save insects an unnecessary flower-call! The colour usually changes due to oxidation of pigment; trillium turns pink; peyote cactus closes after five seconds, Magnolia virginianum is brown within half an hour; speedwell goes from blue to purple; milkwort gets a redflush; and the erythronium stem becomes erect, while others give off an odour.
Pollinizers and devices: some flowers have an obstacle course before an insect collects its reward. The Aroids generate a warmth within the spathe, releasing an odour and luring the insect which then slips on the oily exudate into the lower chamber where the stigma is. The insect is trapped all night by the hair guards. In the morning the hair guards collapse, and the insect escapes, after inadvertently gathering the pollen. Some flowers, such as gentian and aquilegia, have translucent, window-like areas around the sexual organs to lure insects already in the flower and looking for an exit.
Canadian alpines: study of these flowers early in the season found many insects competing for a meagre supply of pollen and nectar, while later in June, there is a cornucopia of species in bloom with unlimited supplies.
Bees: four wings (flies have two), with 100 times our sense of smell. Red looks black to them; a yellow dandelion is purple; and their eyes are sensitive to ultraviolet light so they see markings (nectar guides) invisible to our eyes. They have a honey crop in their alimentary tract and pollen 'baskets' on their hind legs held on by bristles which are very visible if you watch them in summer. They visit the same kind of flower for several days, thereby wasting no pollen or energy. There are no bees or bumblebees at high altitudes.
Hawkmoths: speedy workers, visiting 106 flowers in four minutes! (See Note 2 below)
Moths: usually work nocturnally on the wing.
Butterflies: sit to feed; like red colours.
Flies: two wings and delight in visiting flowers that smell of carrion, such as skunk cabbage.
Hummingbirds: 70 wing beats per second! They have a tubular tongue which aspirates the watery nectar; they also prefer the colour red. It is interesting to note the placement of pollen that they collect while they are sipping their nectar; with honeysuckle the pollen sticks to the corner of their mouth, while with Indian paintbrush it is found on their forehead.
Wind: for millions of years (before insects and other pollinators existed), the only way to cross-pollinate plants; this method includes nearly all the trees and grasses. The pollen is light and dry to help it fly through the air. Wind pollination is also useful where insects are scarce due to cold. Pollination most often takes place before the emergence of the leaves to facilitate the passage of pollen; petals are small or non-existent, because no landing stage or nectar guides are needed; calyces are tough to protect the early flowers from cold; pistils are furry, rigid and carried above the stamens while they dangle and sway in the wind to release clouds of pollen.
Cleistogamy: 'closed marriage', when self-fertilisation takes place within an unopened flower. We find examples with violets and dandelions. (See Note 3 below.)
NOTES Updated 2013 (RP):
I could not substantiate the details of Erica’s notes on 'Nectar' specifically – as I could not find Von Frisch’s research regarding this. However, different species of plants do have different times during the day that they peak in nectar production, and Von Frisch is famous for his work with bees – particularly describing the 'waggle dance' around 1927.
I could not substantiate the hawk moth speed of visiting flowers (106 in 4 minutes) – but they are known for speed, and I found a references of hummingbirds visiting 50 flowers per minute. Some hawk moths, such as the hummingbird hawk moth, hover in midair while they feed on nectar from flowers, so are sometimes mistaken for hummingbirds. This hovering capability has evolved only four times in nectar feeders: in hummingbirds, certain bats, hoverflies, and hawk moths. This is an example of convergent evolution.
Advantage is the plant can use less of its resources, as development of petals, nectar and large amounts of pollen are not required. The disadvantage is the lack of genetic variation that results.
(MG) Bees use sonication (buzz pollination), especially with tomatoes and blueberries.