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 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 indigenous vegetation where it becomes established. 
Great Fertility not essential to Rapid 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 following account 
of one of its breeding places and migrations by the celebrated 
