In Darwin's famous book
titled "The Various Contrivances by which British and Foreign Orchids are Fertilised by Insects and on the Good Effects of Intercrossing
" (Published in London by John Murray (1862
.) the frequently referred to but by most of the referrers hardly if ever cited text runs as follows.
"The Angraecum sesquipedale
, of which the large six-rayed flowers, like stars formed of snow-white wax, have excited the admiration of travellers in Madagascar, must not be passed over. A green, whip-like nectary of astonishing length hangs down beneath the labellum. In several flowers sent me by Mr. J. Bateman
I found the nectaries eleven and half inches long, with only the lower inch and a half filled with nectar.
What can be the use, it may be asked, of a nectary of such disproportionate length? We shall, I think, see that the fertilisation of the plant depends on this length, and on nectar being contained within the lower and attenuated extremity. It is, however, surprising that any insect should be able to reach the nectar. Our English sphinxes have proboscides a long as their bodies; but in Madagascar there must be moths with proboscides capable of extension to a length of between ten and eleven inches! This belief of mine has been ridiculed by some entomologists, but we now know from Fritz Müller that there is a sphinx-moth in South Brazil which has a proboscis of nearly sufficient lenght, for when dried it was between ten and eleven inches long. When not protruded it is coiled up into a spiral of at least twenty windings."
Then Darwin describes how he experimented with a "... a cylindrical rod one tent of an inch in diameter
..." to imitate the proboscis of a large moth and how he succeded in removing then attaching the pollinia to the stigma. Darwin was so elated by his success that the last, uninterrupted paragraph closing this subject became a stylistics monster running through more than one full page of the small format book.
True to his form, here Darwin is highly anthropocentric and teleological
again. Realizing his underlying presuppositions would call for supernatural mental abilities enabling living creatures to modify their genetically determined properties at will - by dreaming up and setting aims then undretaking transformations pointig towards specific goals. Of course in Darwin's time the biochemistry of genetical processes was absolutely unknown. Having said so, here comes a lengthy tirade on the supposed co-evolution of this orchid and at the time of writing still unknown giant moth:
"If such great moths were to become extinct in Madagascar, assuredly the Angraecum
would become extinct. On the other hand, as the nectar, at least in the lower part of the nectary is stored safe from the depredation of other insects, the extinction of the Angraecum
would probably be a serious loss to these moths. We can thus understand how the astonishing length of the nectary had been acquired by successive modifications. As certain moths of Madagascar became larger through natural selection in relation to their general conditions of life, either in the larval state, or as the proboscis alone was lengthened to obtain honey from the Angraecum
and other deep tubular flowers, those individual plants of Angraecum
which had the longest nectaries (and the nectary varies much in some Orchids), and which, consequently, compelled the moths to insert their proboscides up to the very base, would be fertilised. These plants would yield most seed, and the seedlings would generally inherit long nectaries; and so it would be in successive generations of the plant and of the moth. Thus it would appear that there has been a race in gaining length between the nectary of the Angraecum
and the proboscis of certain moths; but the Angraecum
has triumphed, for it flourishes and abounds in the forests of Madagascar, and still troubles each moth to insert its proboscis as deeply as possible in order to drain the last drop of nectar."
The speculations of Darwin based on his experiments concerning the existence of a giant moth in Madagascar were corroborated only eleven years later, when the indeed nocturnal hawk-moth, the pollinator of Angraecum sesquipedale
was discovered and described for science no less than fifty-five years after Darwin's prediction. Since then the valid scientific name of this hawk moth is Xanthopan morganii praedicta
Rothschild et Jordan (1903
.), in honor of Darwin's prediction.
, so far neither Angraecum sesquipedale
nor Xanthopan morganii praedicta
seem to be aware of the genial breeding program Darwin devised for them. Which is a great pity because in that way their evolution remains exposed to the vagaries of unpredictable mutations - not controllable by occult powers at will ...