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as far as I have seen, the labellum is either thick and fleshy or is furnished with excrescences. The labellum, for instance, of Oncidium and of Odontoglossum offers all sorts of singular protuberances. In Calanthe we have (Fig. XXIV.) a cluster of odd little spherical warts on the labellum, together with an extremely long nectary, which does not include nectar; in Eulophia viridis the short nectary is in the same condition, and the labellum is covered with longitudinal and fimbriated ridges. In some also of the Ophreæ, which have no nectary, the labellum, as in the Fly Ophrys, has two shining protuberances at its base, placed beneath the two pouches. Lindley has remarked that the use of these strange and diversified excrescences is quite unknown.
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<section begin="chapter6"/>
as far as I have seen, the labellum is either thick and fleshy or is furnished with excrescences. The labellum, for instance, of Oncidium and of Odontoglossum offers all sorts of singular protuberances. In Calanthe we have (Fig. XXIV.) a cluster of odd little spherical warts on the labellum, together with an extremely long nectary, which does not include nectar; in Eulophia viridis the short nectary is in the same condition, and the labellum is covered with longitudinal and fimbriated ridges. In some also of the Ophreæ, which have no nectary, the labellum, as in the Fly Ophrys, has two shining protuberances at its base, placed beneath the two pouches. Lindley has remarked that the use of these strange and diversified excrescences is quite unknown.
From the position, relative to the viscid disc of the pollinium, which these excrescences hold, and from the absence of nectar, it seems to me highly probable that they afford food, and thus attract either Hymenoptera or flower-feeding Coleoptera. I mention this belief because a close examination of the flowers of the Vandeæ, which in their native country have had their pollinia removed, would soon settle this point. There is no more inherent improbablity in a flower being habitually fertilised by an insect coming to feed on the labellum, than in seeds being habitually disseminated by birds attracted by the sweet pulp in which they are embedded. But I am bound to state that Dr. Percy had the thick and furrowed labellum of a Warrea analysed for me, by fermentation over mercury, and it gave no evidence of containing more saccharine matter than the other petals. On the other hand, the thick labellum of Catasetum, and even the bases of the upper petals in Mormodes ignea, had, as previously stated, a slightly sweet, rather pleasant, and nutritious taste.
From the position, relative to the viscid disc of the pollinium, which these excrescences hold, and from the absence of nectar, it seems to me highly probable that they afford food, and thus attract either Hymenoptera or flower-feeding Coleoptera. I mention this belief because a close examination of the flowers of the Vandeæ, which in their native country have had their pollinia removed, would soon settle this point. There is no more inherent improbablity in a flower being habitually fertilised by an insect coming to feed on the labellum, than in seeds being habitually disseminated by birds attracted by the sweet pulp in which they are embedded. But I am bound to state that Dr. Percy had the thick and furrowed labellum of a Warrea analysed for me, by fermentation over mercury, and it gave no evidence of containing more saccharine matter than the other petals. On the other hand, the thick labellum of Catasetum, and even the bases of the upper petals in Mormodes ignea, had, as previously stated, a slightly sweet, rather pleasant, and nutritious taste.
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great vertebrate class of Fish, or still more appropriately with tropical Homopterous insects, which seem to
great vertebrate class of Fish, or still more appropriately with tropical Homopterous insects, which seem to
us in our ignorance as if modelled by the wildest caprice.
us in our ignorance as if modelled by the wildest caprice.
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{{larger|'''CHAPTER VII.'''}}
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<section begin="chapter7"/>
{{larger|'''CHAPTER VII.'''}}
Homologies of Orchid-flowers—The great modification which they have undergone—Gradation of organs, of the rostellum, of the pollen-masses—Formation of the caudicle—Genealogical affinities—Mechanism of the movement of the pollinia—Uses of the petals—Production of seed—Importance of trifling details of structure—Cause of the vast diversity of structure for the same general purpose—Cause of the perfection of the contrivances in Orchids Summary on insect-agency Nature abhors perpetual self-fertilisation.
Homologies of Orchid-flowers—The great modification which they have undergone—Gradation of organs, of the rostellum, of the pollen-masses—Formation of the caudicle—Genealogical affinities—Mechanism of the movement of the pollinia—Uses of the petals—Production of seed—Importance of trifling details of structure—Cause of the vast diversity of structure for the same general purpose—Cause of the perfection of the contrivances in Orchids Summary on insect-agency Nature abhors perpetual self-fertilisation.
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The importance of the science of Homology rests in its giving us the key-note of the possible amount of difference in plan within any group; it allows us to class under proper heads the most diversified organs; it shows us gradations which would otherwise have been overlooked, and thus aids us in our classification; it explains many monstrosities; it leads to the detection of obscure and hidden parts, or mere vestiges of parts, and shows us the meaning of rudiments. Besides these practical uses, to the naturalist who believes in the gradual modification of organic beings, the science of Homology clears away the mist from such terms as the scheme of nature, ideal types, archetypal patterns or ideas, etc.; for these terms come to express real facts. The naturalist, thus guided, sees that all homological parts or organs, however much diversified, are modifications of one and the same ancestral organ; in tracing existing gradations he gains a clue in tracing, as far as that is possible, the probable course of modification during a long line of generations. He may feel
The importance of the science of Homology rests in its giving us the key-note of the possible amount of difference in plan within any group; it allows us to class under proper heads the most diversified organs; it shows us gradations which would otherwise have been overlooked, and thus aids us in our classification; it explains many monstrosities; it leads to the detection of obscure and hidden parts, or mere vestiges of parts, and shows us the meaning of rudiments. Besides these practical uses, to the naturalist who believes in the gradual modification of organic beings, the science of Homology clears away the mist from such terms as the scheme of nature, ideal types, archetypal patterns or ideas, etc.; for these terms come to express real facts. The naturalist, thus guided, sees that all homological parts or organs, however much diversified, are modifications of one and the same ancestral organ; in tracing existing gradations he gains a clue in tracing, as far as that is possible, the probable course of modification during a long line of generations. He may feel
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<section end="chapter7"/>