Erica's Original Notes Flowers of today are the end result of slow evolutionary pressures down through millions of years of growth and natural selection.
Flowers are the ephemeral sexual display in the yearly cycle of the plant's life; the design of flowers is complex, with some flowers even indicating where the nectar/pollen is to be found and where the insect should land and taxi in (nectar guides). Some have quite an obstacle course to complete before the insect gets its reward! As to shape, they are either zygomorphic (bilaterally symmetrical) or actinomorphic (regular/radially symmetrical).
Parts of the flower have changed by slow adaptation over the ages >>
Calyx protects the flower bud and is formed of sepals.
Corolla: made up of the petals which are the flower's advertising billboard to the pollinators flying by.
Stamens: the male organ of the flower producing pollen.
Stigma: the receptive surface for pollen which is part of the female carpel.
Position of ovary:
hypogynous: sepals and petals attached below the ovary, e.g. tulip;
epigynous: sepals and petals inserted above the ovary, e.g. daffodil;
perigynous: sepals and petals inserted around the ovary, e.g. rose; flowers remain in bud until the ovules are old enough to consider matrimony; male and female parts may mature at different times to avoid self-pollination; some stigmas inhibit pollen from the same plant.
Nectar: made by flowers to encourage air mail delivery of pollen by insects and other pollinators.
Sparks of light and luminosity have been observed during warm summer nights, presumably when essential oils are evaporating, from tuberoses, sunflowers, evening primroses and red poppies. The daughter of Linnaeus saw sparks of light coming from nasturtiums on a warm, stormy night. (See Note 1 below):
Conifers do not have flowers but strobili, or cones. The female cone is composed of loosely fitting ovule-bearing scales with narrow slits (micropyles, like little doors), near which the pollen grain falls, the scales fill with resinous fluid which dries and draws the pollen into the slit, which then closes. In the first spring the pollen enters the cone; in the second, spring fertilization takes place; this is a complicated arrangement, but it must work, otherwise Nature would have given up the practice! (See Note 2 below.)
Primitive flowers can be recognized by the fact that they have many stamens and no honey guides, such as magnolias and buttercups.
Flower clocks: Some flowers have regular 'opening times': Kalanchoe opens and closes according to day length; some flowers won't open unless the day temperature reaches 68 degrees Fahrenheit firs. The dandelion starts to open at 50 degrees, and is fully open at 64 degrees, making us all feel sunny. Others open with special humidity conditions, when pollinators are abroad and in response to internal rhythms.
Flower colours are made of the same chemical pigments that colour the leaves, only with the leaves the colour is masked by the chlorophyll; anthocyanins which are the pigments responsible for flower colour in most flowers are seen as blue, red, purple depending on the acidity in flowers. A purple tulip is different – it has cells of red and blue much like a Seurat painting. White flowers have no colour pigments. Air spaces scatter light rays, making them more striking, just as in birds' feathers, and known as molecular colouring. Ultraviolet bands of colour found, for example, on daisies, are invisible to the human eye, but are seen by the bee who uses them as a nectar guide.
NOTES Updated 2013 (RP):
Sparks of light caution. Although references matching Erica’s notes and dating to late 1800s were found, no recent scientific explanations were found for this phenomenon in the more recent literature.
Some conifers lack the pollination droplet mechanism that Erica describes. Douglas-fir pollen grains land on an enlarged, stigma like growth of the micropyle, from which the pollen tubes grow to fertilize the ovule. The pollen grains of the Araucariaceae land on the scales of the female cone, and the pollen tubes reach the micropyle by growing into the cone scales. The time from pollination to fertilization can exceed a year but this is not the case for all conifers.