necessary consequence? That of the myriad seeds produced only a few will develop into seed-bearing plants; each seed needs a certain proportion of soil, moisture, air, light; if they fall round the parent stem and sprout into seedlings, they so crowd each other that the weaker perish; every gardener knows that his seedlings need thinning if any are to grow into useful plants, that his plantations must be thinned out, if any tree is to have full development; an overcrowded plantation, an overcrowded garden-bed, gives a crop of dwarfed, stunted, weak, and useless plants. These facts are so commonplace that they pass continually before our eyes, and the simple inference from them is unregarded. There is another check of a severe character on vegetable increase. Birds eat the seeds; animals browse on the plants; man uses many kinds for his own support; the wheat sown in one year, not only produces the seed corn for the ensuing season, but also affords so vast a multiplication as to supply the world with bread; the animal world preys on the vegetable, and so is made a check which destroys the mature, as well as the check of want of room and nourishment which destroys the infant, growth. Out of 357 seedlings of English weeds, carefully watched by Mr. Darwin, 295 were destroyed. On some heaths near Farnham, in the portions enclosed during ten years previously, self-sown firs were observed by him springing up so closely that all could not live, while in the unenclosed portions not one young tree was to be seen. On close examination, Mr. Darwin found, in one square yard, thirty-two little trees, no higher than the heather, one with twenty-six rings of growth: the check here was the browsing of cattle over the open parts of the heath. In the animal kingdom the same class of checks is found: the rabbit which in Australia has become an intolerable plague, is kept down to a fair level in England, not because he multiplies less rapidly, but because the check of destruction is brought to bear upon him; food is scarcer in the more cultivated land; guns and traps send him to the market in millions; hawks, weasels, cats, prey upon his young; he produces life rapidly, but the check of death waits upon him and keeps him down. The swift increase of plants and animals under favourable circumstances, dealt with in Chapter I., shows the enormous power of the destructive checks which generally keep in subjection the life-producing force. Once more turning to Mr. Darwin, we read:—
"Of the many individuals of any species which are
