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Show 418 HABITS OF INSECrrs CHAP. XI. surface of the bag. I then gathered a spathe and breathed hard into it; ~everal flies soon crawled out, and. all without exception were dusted with arum pollen. These flies quickly flew away, and I distinctly saw three of them fly to another plant about a yard off; they alighted on the inner or concave surface of the spathe, and suddenly flew down into the flo:wer. I th~n opened this flower, and although not a single anther had burst, several grains of pollen were lying at the bottom, which must have been brought fro1n another plant by one of these flies or by some other insect. In another flower little flies were crawling about, and I saw them leave pollen on the stigmas. I do not know whether Lepidoptera generally keep to the flowers of the same species; but I once observed 1nany minute moths (I believe Lampronia Cfi1~e~) calthella) apparently eating the pollen of Merc~~rwl~s annua, and th y had the whole front of their bodies covered with pollen. I then wont to a fon1ale plant some yards off, and saw in the cours~ of fifteen ~inutes three of these moths alight on the stigmas. Lepidoptera are probably often induced to frequent ~he Ho':m·s of the same species, whenever these are provided with a long and narrow nectary, a(; in this case other insects cannot suck the nectar, which will thus be preserved for those having an elongated proLoseis. No doubt the.! ucca 1noth * visits only the flowers whence its nam~ IS derived, for a most wonderful instinct guides this moth to place pollen on the stigma, so that the ~vules may be developed on which the larvm feed. vVIth ~espect to Coleoptera I have seen Meligethes covered w1th pollen flying from' flower to flower of the same spem. es; an d * Describe<l hy 1\lr. Riley in the ' A mm·1· ean Naturalist,' .vol. vii. Oct. 1873. CHAP. XI. IN RELATION TO CROSS-FERTILISATION. 419 ~~is must often o.ccur, as, according to M. Brisout, many of the species affect only one kind of plant."* It ~ust not be.supposed from these several statements that. Insects stnctly confine their visits to the same species. They often visit other species when only a few plants of the same kind grow near together. In a flower-garden containing some plants of CEnothera the pollen. of which can easily be recognised, I found' not only s:ngle grain_s ?ut masses of it within many flowers of Mimulus, Digitalis, Antirrhinum, and Linaria. Other kinds of pollen were likewise detected in these same flowers. A large number of tho stigmas of a plant of Thyme,i~ which the anthers were completely aborted, were examined ; . and these stigmas, though scarcely larger than a spht needle, were covered not only with polle~ of Thyme brought from other plants by the bees, but with several other kinds of pollen. · That insects should visit the flowers of the same species as long as they can, is of great importance to the plant, as it favours the cross-fertilisation of distinct individuals of the same species; but no one will suppose that insects act in this manner for the good of the plant. The cause probably lies in insects being thus enabled to work quicker; they have just learnt how to stand in the best position on the flower, and how far and in what direction to insert their proboscides.t They act on the same principle as does an artificer who has to make half-a-dozen engines, and who saves time by making consecutively each wheel and part for all of them. Insects, or at least bees, seem 1nuch influenced by habit in all their manifold operations; and * As quoted in' American Nat.' May 1873, p. 270. t Since these remarks were written, I find that H. Miiller has come to almost exactly the same conclusion with respec.t to the cause of insects frequenting nA long as they can the flowers of the same species: ' Bienen Zeitung,' July 1876, p. 182. 2 E 2 |