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Show 30 DARWINISM CHAP. from the West Indies, which appears to have found in Ceylon a soil and climate exactly suited to it. It now covers thous;LIHh of acres with its dense masses of folbge, taking complete possession of land where cultivation has been neglected or abandoned, preventing the growth of any. ot~er plants, arHl even destroyinO' small trees, the tops of whiCh 1ts subscandeni sterns are able to reach. The fruit of this plant is so ace pt able to frugivorous birds of al.l kinds that, through their i~1 strnmentality, it is spreading rap1dly,. to the complete ~xclus10n of the indigenous vegetation where 1t becomes established. Great Fertility not essen tial to Rapid Inc1·ease. The not uncommon circumstance of slow-bre cling anim:.tls beinO' very numerous, shows that it is usually the ttmonnt of d~struction which an animal or plant is expo eel to, not its rapid multiplication, that determines its nnmb rs in nny country. The passenger-pigeon (Ectopistos migratorius) is, or rather was, excessively abundant in a certain area in North America, and its enormous migrating flocks darkening tho sl\y for hours have often been described; yet this bird lays only two eggs. The fulmar petrel is supposed to be one of the most numerous birds in the world, yet it lays only one egg. On the other hand the great shrike, the tree-creeper, the nut-batch, the nut-cracker, the hoopoe, and many other bircls, lay from four to six or seven eggs, and yet arc n ver abundant. So in plants, the abundance of a species bears little or no relation to its seed-producing power. Some of the grasses and sedges, the wild hyacinth, and many bnttercnps occur in immense profusion over extensive areas, although each plant produces comparatively few seeds ; while seveml species of bell -flowers, gentians, pinks, and mulleins, and even :ome of the compositre, which produce an abundance of minnte seeds, many of which are easily scattered by the wind, m·e yet rare species that never spread beyond a very limited :u·e;t. The above-mentioned passenger-pigeon affords snch :m excellent example of an enormous bird-popnlation kept np lly a comparatively slow rate of increase, and in ·pite of il s complete helplessness and the great destruction whidl iL snffers from its numerous enemies, that the following :H:cmutt of one of its breeding-places and migrations by the celebrated II THE STRUGGLE FOR EXISTENCE 31 American naturalist, Alexander Wilso11, will be read with interest:- " Not far from Shelbyville, in the State of Kentucky, about five years ago, there was one of these breeding-places, which stretched through the woods in nearly a north and south direction, was several miles in breadth, and was said to be upwards of 40 miles in extent. In this tract almost every tree was furnished with nests wherever the branche~ could accommodate them. The pigeons made their first appearancD there about the 1Oth of April, and left it altogether with their young before the 25th of May. As soon as the young were fully grown and before they left the nests, numerous parties of the inhabitants from all parts of the adjacent country came with waggons, axes, beds, cooking ute?sils, J?~ny of them accompanied by the greater part of thmr fam!lJCs, and encamped for several days at this immense nursery. Several of them informed me that the noise was so great as to terrify their horses, and that it was difficult for one person to hear another without bawling in his ear. The ground was strewed with hroken limbs of trees, eO'O'S and b . h' bb' young squ~ p1geons, w 1ch hau been precipitated from above, and on whiCh herds of hogs were fattening. Hawks, buzzards and eagles were sailing about in great numbers, and seizin~ the squabs from the nests at pleasure; while, from 20 feet upwards to the top of the trees, the view through the woods presented a perpetual tumult of crowdinO' and flutterinrr multitudes of pigeons, their wings roarin~ like thunder mingled with the frequent crash of falling timber; for no"~ the axemen were at work cutting down those trees that seemed most crowded with nests, and contrived to fell them in such a manner, that.in their descent they might bring down several o.tbers ; by whiCh means the falling of one large tree sometr. mes produced 200 squabs little inferior in size to the old btrds, and almost one heap of fat. On some single trees upwards of a h~ndred nests were found, each containing one squab only; a Circumstance in the history of the bird not generally known to naturalists.1 It was dangerous to walk ·ou~ La:er observers. have proved that two eggs are laid and usual~ two ) g.ploduced, but 1t may be tl1at iu most cases only one of these cou1es to matunt y. |