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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Fertilisation of Orchids | 5/9 | https://en.wikipedia.org/wiki/Fertilisation_of_Orchids | reference | science, encyclopedia | 2026-05-05T08:30:38.882356+00:00 | kb-cron |
A poet might imagine, that whilst the pollinia are borne from flower to flower through the air, adhering to a moth's body, they voluntarily and eagerly place themselves, in each case, in that exact position in which alone they can hope to gain their wish and perpetuate their race. This is followed by descriptions of the differences in the mechanisms of several other orchids. In Orchis pyramidalis, the adhesive balls are combined into a strap or saddle shape, which curls round the thin proboscis of a moth or butterfly to attach to it the pair of pollen masses, illustrated in the book by figure 4 showing a moth's head with seven pairs of pollen masses attached to its proboscis.
While the bee orchid showed adaptation for self-fertilisation, its mechanism also enabled occasional cross-fertilisation, creating the biological diversity that Darwin felt was needed for vigorous survival, which could not be provided by self-fertilisation. As an example of "how beautifully everything is contrived", Darwin described how he had found that in Spiranthes flowers the pollen is ready for collection before access is open for the female organ to receive pollen. At Torquay he had watched bees visiting spires of these flowers, starting at the bottom of the spire and working their way up to the topmost flowers. He speculated that if bees moved from top to top of the spires, the pollen clusters they collected from the most recently opened flowers would be wasted as the topmost flowers on the next spike would not be ready to receive pollen. A bee starting at the lowest flowers on the first spire it visited would continue up until it reached flowers that still had their pollen masses to attach to the bee, then would fly to the mature lower flowers on another plant, and fertilise them. By this co-ordinated process, the bee would add "to her store of honey" while perpetuating the flowers "which will yield honey to future generations of bees".
=== Exotic orchids ===
The book moves on to the various foreign orchids Darwin had received from others. His experiments showed that the "astonishing length" of the 111⁄2 inch (290 mm) long nectary hanging from Angraecum sesquipedale flowers implied the need for an as yet unknown moth with a proboscis 10–11 inches (250–280 millimetres) long to pollinate these flowers in Madagascar. He viewed this as the outcome of a coevolutionary race, writing that "there has been a race in gaining length between the nectary of the Angræcum and the proboscis of certain moths". This wastefulness is familiar in modern terms as the idea of an evolutionary arms race, but was disturbing to biologists of the time who believed that adaptations were the outcome of benevolent divine purpose. Darwin described "the most remarkable of all Orchids", Catasetum, and showed how in these flowers, "as throughout nature, pre-existing structures and capacities [had been] utilised for new purposes". He explained the mechanism in which the pollen masses of the pollinium were connected by a bent stalk or pedicel to a sticky disc kept moist at the back of the flower. When an insect touched an "antenna" projecting from the back of the flower, this released the bent pedicel which sprang straight and fired the pollinium, sticky disc first, at the insect. In experiments, Darwin had imitated this action using a whalebone spring. He vividly illustrated how the flower ejected the pollinium with considerable force: "I touched the antennæ of C. callosum whilst holding the flower at about a yard's distance from the window, and the pollinium hit the pane of glass, and adhered to the smooth vertical surface by its adhesive disc."