experiments on a large scale on variability in plants, and the results of those experiments have enabled him to formulate gradually his own thoughts and to compare them with the teachings of Darwin, Wallace and others. Those who are acquainted with the patient experiments of the Amsterdam professor and have assimilated his results, will agree that, by the publication of this book, a new leaf has been turned *in the history of evolution. A set of new facts has been gathered with which all those who of late years have theorized about Darwinism must reckon, and which will undoubtedly prove to be the starting-point for further experiments in the direction they so clearly indicate.
I shall now try to point out: (1) in what respects de Vries's work is such a very decided step in advance; (2) in how far it might be supposed that there is any conflict between Darwin's opinions and those of de Vries; and (3) to what extent a teleological interpretation of nature might draw upon the results of de Vries's investigations.
Supposing there existed no variability in nature, life would lose a good many of its attractions. Fancy men and women resembling each other like so many drops of water, both physically and morally! Fancy all dogs constructed according to one pattern, all flowers, all trees of one species being absolutely identical as to their branches, number and shape of leaves, etc.! Fortunately, from our very childhood we have learnt to see nature in a different light, and we have all contracted the habit of giving our preference to the finest and best horses, flowers and playfellows; permanent selection is thus being exercised by us, which can add much to our happiness in life. In effecting it, we make use of what variability offers, and, consciously or unconsciously, we always tend to favor the better and to decline the worse.
Yet more intensely than in the way just sketched, the variability of living organisms is utilized by those who make their livelihood by the rigorous application of selective principles to plants and animals. Dealers in seeds of improved plants, nursery gardeners who cultivate rare varieties of flowers, breeders of birds and domestic animals, all these have a direct interest in every change for the better or for the worse, and are very keen at increasing the former and eliminating the latter. Any one who sells corn or maize, which, when sown under the same conditions, produces ears doubly full or yielding flour of a better quality, may be certain of a substantial gain. One who cultivates beet-roots containing a greater amount of sugar gains equally. Again, a man who lays out a considerable amount of money in purchasing mares and stallions beautifully fit for racing purposes, and who breeds from these with care, will not only be paid back the money he spent, but find means of quickly doubling his capital.
The improvement of our domestic animals, the development of our wheat, the diversity in color and in shape of our decorative plants,