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Show 318 DARWINISM CHAP. insects that most abound where they grow. Thus the gentians of the lowlands are adapted to bees, those of the high alps to butterflies only; and while most species of Rhinanthus (a aenus to which our common "yellow rattle" belongs) are beeflowers, one high alpine species (R. alpinus) has been also adapted for fertilisation by butterflies only. The reason of this is, that in the high alps butterflies are immensely more plentiful than bees, and flowers adapted to be fertilised by bees can often have their nectar extracted by butterflies without effecting cross-fertilisation. It is, therefore, important to have a modification of structure which shall make butterflies the fertilisers, and this in many cases has been donc.t 9. Economy of time is very important both to the insects and the flowers, because the fine working days are comparatively few, and if no time is wasted the bees will get more honey, and in doing so will fertilise more flowers. Now, it has been ascertained by several observers that many insects, bees especially, keep to one kind of flower at a time, visiting hundreds of blossoms in succession, and passing over other species that may be mixed with them. They thus acquire quickness in going at once to the nectar, and the change of colour in the flower, or incipient withering when fertilised, enables them to avoid those flowers that have already had their honey exhausted. It is probably to assist the insect. in keeping to one flower at a time, which is of vital importance to the perpetuation of the species, that the flowers which bloom intermingled at the same season are usually very distinct both in form and colour. In the sandy districts of Surrey, in the early spring, the copses are gay with three flowers-the primrose, the wood-anemone, and the lesser celandine, forming a beautiful contrast, while at the same time the purple and the white dead-nettles abound on hedge banks. A little later, in the same copses, we have the blue wild hyacinth (Scilla nutans ), the reel campion (Lychnis dioica), the pure white great starwort (Stellaria Holosteum), and the yellow dead-nettle (Lamium Galeobdolon), all distinct and well-contrasted flowers. In damp meadows in summer we have the ragged robin (Lychnis Floscuculi), the spotted orchis (0. maculata), and the yellow rattle (Rhinanthus 1 " Alpenblumen," by D. H. Muller. See Natu1·e, vol. xxiii. p. 333. XI THE SPECIAL COLOURS OF PLANTS 319 Crista-ga~li); ·while in drier meadows we have cowslips, ox-eye daisies, and buttercups, all very distinct both in form and colour. So in cornfields we have the scarlet poppies, the purple corn-cocl~le, the yellow corn-maryg-old, and the blue cornflower; while on our moors the purple heath and the dwarf gorse make a gorgeous contrast. Thus the difference of co~our v~hich enables the insect to visit with rapidity and unerrmg mm a number of flowers of the same kind in succession, serves to adorn our meadows, banks, woods and heaths with a charming variety of floral colour and fo;m at each season of the year. I Fe1·tili ·at ion of Flowers by Bin! s. In the temper.ate regions of the Northern Hemisphere, insects are the chief agents in cross-fertilisation when this is not effected by the wind ; but in warmer regions, and in the Southern hemisphere, birds are found to take a considerable part in the operation, and have in many cases led to modifications in the form and colour of flowers. Each part of the globe has special groups of birds which are flower-haunters. America has the humming-birds (Trochilidre), and the smaller group of the sugar-birds (Crerebiclre). In the Eastern tropics t~e sun-birds (Nectarineidre) take the place of the 4ummingb1rds, and another small group, the flower-peekers (Dicreidre ), assist them. In the Australian region there are also two flower-feeding greups, the Meliphagidre, or honey-suckers, and the brush-tongued lories (Trichoglossidre). Recent researches by American naturalists have shown that many flowers are fertilised by humming-birds, such as passionflowers, trumpet-flowers, fuchsias, and lobelias; while some, as the Salvia splenclens of Mexico, are specially adapted to their visits. We may thus perhaps explain the number of very large tubular flowers in the tropics, such as the huge brugmansias and bignonias; while in the Andes and in 1 This peculiarity of local distribution of colour in flowers may be compared, as regards its purpose, with the recognition colours of animals. Just as t~ese latter colours enable the sexes to recognise each other, and thus avoid sterile unions of distinct species, so the distinctive form and colour of each species of flower, as compared with those that usually grow around it, enables the fertiliRing insects to avoid carrying the pollen of one flower to the stigma of a distinct species. |