In it, I rather briefly mention Darwin's interest in orchids. Seeing as I have a blog on that subject, I thought it might make an interesting post...
Darwin devoted significant research to this group of plants, as you can see over at Darwin Online, which freely publishes much of Darwin's work online in electronic format. In particular, his interest was in how orchids are fertilised (in the wild), which is indeed a fascinating topic. He spent around 10 months of his time absorbed solely by that subject, which ultimately culminated in a book, On the various contrivances by which British and foreign orchids are fertilised by insects, and on the good effects of intercrossing, which was published after his most famous work. In it, he adds further weight to his concepts around the necessity for sexual reproduction to maintain "fitness" - remember, he made these intellectual connections without any knowledge of genes or DNA:
"THE object of the following work is to show that the contrivances by which Orchids are fertilised, are as varied and almost as perfect as any of the most beautiful adaptations in the animal kingdom; and, secondly, to show that these contrivances have for their main object the fertilisation of each flower. In my volume 'On the Origin of Species' I have given only general reasons for my belief that it is apparently a universal law of nature that organic beings require an occasional cross with another individual; or, which is almost the same thing, that no hermaphrodite fertilises itself for a perpetuity of generations. Having been blamed for propounding this doctrine without giving ample facts, for which I had not, in that work, sufficient space, I wish to show that I have not spoken without having gone into details.Charles Darwin (1862) On the various contrivances by which British and foreign orchids are fertilised by insects, and on the good effects of intercrossing. London: John Murray pp1-2.
I have been led to publish this little treatise separately, as it has become inconveniently large to be incorporated with the rest of the discussion on the same subject. And I have thought, that, as Orchids are universally acknowledged to rank amongst the most singular and most modified forms in the vegetable kingdom, the facts to be presently given might lead some observers to look more curiously into the habits of our several native species. An examination of their many beautiful contrivances will exalt the whole vegetable kingdom in most persons' estimation. I fear, however, that the necessary details will be too minute and complex for any one who has not a strong taste for Natural History. This treatise affords me also an opportunity of attempting to show that the study of organic beings may be as interesting to an observer who is fully convinced that the structure of each is due to secondary laws, as to one who views every trifling detail of structure as the result of the direct interposition of the Creator."
In particular, he was taken in by the extraordinary flowers of the Catasetinae, which to those who are not "orchid geeks" might be unfamiliar - they possess remarkable "hair trigger" mechanisms which effectively "shoot" the pollinator with their polinnia after they touch the mechanism. It's really quite amazing:
Another of the key findings in the book was a prediction - a hallmark of good science:
"I fear that the reader will be wearied, but I must say a few words on the Angræcum sesquipedale, of which the large six-rayed flowers, like stars formed of snow-white wax, have excited the admiration of travellers in Madagascar. A whip-like green nectary of astonishing length hangs down beneath the labellum. In several flowers sent me by Mr. Bateman I found the nectaries eleven and a half inches long, with only the lower inch and a half filled with very sweet nectar. What can be the use, it may be asked, of a nectary of such disproportional length? We shall, I think, see that the fertilisation of the plant depends on this length and on nectar being contained only within the lower and attenuated extremity. It is, however, surprising that any insect should be able to reach the nectar: our English sphinxes have probosces as long as their bodies: but in Madagascar there must be moths with probosces capable of extension to a length of between ten and eleven inches!"Emphasis is mine. Indeed, some time later (1903), this very beast was discovered, initially named Xanthopan morgani praedicta Rothschild & Jordan, 1903. Indeed, fellow "co-inventor" (whose letter on the subject spurred Darwin to get around to publishing his most famous work) of the theory of evolution, and entomologist extraordinare, Alfred Russel Wallace, suggested that it would be a hawkmoth, noting the existence of a moth with a proboscis almost long enough in East Africa; this species and the one from Madagascar are currently considered the same species Xanthopan morgani (Walker 1856). Wikipedia has an article on the beast. And there's also this video:
"If such great moths were to become extinct in Madagascar, assuredly the Angræcum would become extinct. "And indeed, this is a great threat for many such co-dependent species, and one of the many reasons in situ conservation is (wherever possible) always better than captive breeding of the last few of some endangered rarity.
We have an Angraecum sesquipedale - it nearly flowered once... Angraecum longicalcar (which we don't yet have) has an even longer spur - up to 40cm. Somewhere out there in Madagascar must be a moth with an even more impressive "business end"! These interesting relationships are further explored in a 1991 paper by Gene Kritsky, published in American Entomologist, available here.
I won't cover the rest of the book - if this has piqued your interest, you can of course read it yourself!