The Work of Gregor Mendel.--Fifty years ago, an Austrian monk, Gregor Mendel, found in breeding garden peas that these plants passed on certain _fixed characters_, as the shape of the seed, the color of the pod when ripe, and others, and that when two pea plants of different characters were crossed, one of these characters would be likely to appear in the offspring of the second generation in the ratio of three to one. Such characters as would appear to the exclusion of others in the first crossing of the plants were called _dominant_, the ones not appearing, _recessive_ characteristics. When these seeds were again sown the ones bearing a recessive characteristic would produce only peas with this recessive characteristic, but the ones with a dominant characteristic might give rise to a pure dominant or to offspring having partly a dominant and partly a recessive character; pure dominants being to the mixed offspring in the ratio of 1 to 2. The pure dominants if bred with others like themselves would produce only pure dominants, but the cross breeds would again produce mixed offspring of three kinds in the ratio of one dominant to two cross breeds and one recessive. The feature of this work that interests us is that _unit_ characters are passed along by heredity in the germ cells _pure_, that is, unchanged, from one generation to another, and independently of each other. [Illustration: Illustration of Mendel's Law.] Determiners of Character.--A child then resembles his parents in some definite particulars because certain _determiners_ of characters have been present in the germ cells of one of the parents. If the determiner of a certain character is _absent_ from the germ cells of both parents, it will be _absent_ in _all_ of their offspring. These discoveries of Mendel are of the greatest importance in plant and animal breeding because they enable the breeder to isolate certain characters and by proper selection to breed varieties which have these desired characters, instead of waiting for a _chance_ union of the desired characters by nature. Animal Breeding.--It has been pointed out that the domestication of wild animals, the horse, cattle, sheep, goats, and the dog, marked a great advance in civilization in the history of the earth's peoples. As the young of these animals came to be bred in captivity the peoples owning them would undoubtedly pick out the strongest and best of the offspring, killing off the others for food. Thus they came unconsciously to select and aid nature in producing a stronger and better stock. Later man began to recognize certain characters that he wished to have in horses, dogs, or cattle, and so by slow processes of breeding and "crossing" or hybridizing one nearly allied form with another the numerous groups of domesticated animals began to appear. [Illustration: What has resulted from artificial selection among dogs. (After Romanes.)]