30 DARWINISM chap. 



from the West Indies, M'hich a})pears to have found in Ceylon a 

 soil and climate exactly suited to it. It now covers thousands 

 of acres with its dense masses of foliage, taking complete 

 possession of land where cultivation has been neglected or 

 abandoned, preventing the growth of any other plants, and 

 even destroying small trees, the tops of which its subscandent 

 stems are able to reach. The fruit of this plant is so accept- 

 able to frugivorous birds of all kinds that, through their instru- 

 mentality, it is spreading rapidly, to the complete exclusion of 

 the indiii;enous vegetation where it becomes established. 



Great Fertility not essential to Bapid Increase. 



The not uncommon circumstance of slow-breeding animals 

 being very numerous, shows that it is usually the amount 

 of destruction which an animal or plant is exposed to, not 

 its rapid multiplication, that determines its numbers in any 

 country. The passenger-pigeon (Ectopistes migratorius) is, or 

 rather was, excessively abundant in a certain area in North 

 America, and its enormous migrating flocks darkening the sky 

 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-hatch, the nut-cracker, the hoopoe, and many other birds, 

 lay from four to six or seven eggs, and yet are never 

 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 buttercups 

 occur in immense profusion over extensive areas, although each 

 plant produces comparatively few seeds ; while several species 

 of bell-flowers, gentians, pinks, and mulleins, and even some 

 of the composite, which produce an abundance of minute seeds, 

 many of which are easily scattered by the wind, are yet rare 

 species that never spread beyond a very limited area. 



The above-mentioned passenger-pigeon affords such an 

 excellent example of an enormous bird-population kept up by 

 a comparatively slow rate of increase, and in spite of its 

 complete helplessness and the great destruction which it 

 suffers from its numerous enemies, that the folloA\ing account 

 of one of its breeding-places and migrations by the celebrated 



