Mutation
in plant and animal breeding, the theory that new varieties and species arise without intermediate forms. Darwin taught that new forms are evolved slowly; according to the mutation theory they come at a jump. The father of the mutation theory is Hugo de Vries, professor of botany in the University of Amsterdam. He began experiments in 1886 with common toadflax, the irregular "butter and eggs" of the wayside. One side of the corolla is spurred. A fold in the corolla closes the throat. Noting an occasional flower with a five-spurred corolla, De Vries set to work to see what he could do toward producing a five-spurred toadflax. He removed to his garden the roots of a few plants that had been observed to bear a five-spurred blossom or two. The seeds of these plants were saved and planted. Omitting accounts of pollination, in the third generation he had a plant that produced as usual many flowers, one of them a five-spurred flower. Seeds from this plant only were sown. In the next generation, the fifth, there were two plants with a five-spurred flower or two. Seed from these only were saved. In the sixth generation, all the flowers were plainly one-spurred. No progress had been made seemingly. In 1894, however, there were scattering peloric flowers on eleven different plants, and there was one plant bearing five-spurred flowers only. This plant and its descendants continued to bear five-spurred flowers only. De Vries in this way established a new variety of toadflax, and it came, not by a gradual change, but at a leap, and De Vries was there to see it.
Extended experiments were conducted by this distinguished botanist with other plants, notably the common cornflower or corn-marigold of Europe. Observing that the florets in the ring around the head varied in number, he undertook to produce corn-marigold with heads covered with florets. Out of three hundred plants, he selected six whose heads bore on an average twenty-one florets. The seeds of each were sown in a plot, and two of the best plants in the best plot were selected--best in this case meaning the plants whose heads averaged the greatest number of florets. Proceeding year by year, in 1897, the number of rays suddenly began to increase by leaps, 21, 34, 48, 66, the florets scattered over the disk; 100, 200, in a word a completely double variety had been produced, practically at a jump.
De Vries has taught that we may expect sports to appear suddenly, and that by watching for them and by caring for them, we may obtain new varieties and new species. De Vries conducted experiments, also, with Lamarck's evening primrose. He sums up his theory of mutation or change as follows:
1. New elementary species appear suddenly without intermediate steps. 2. New forms spring laterally from the main stem and leave the old species to go on in the same old way. 3. New elementary species attain their full constancy at once. Constancy is not the result of selection or of improvement. It is a quality of its own. The tendency must be present in the old species as the tendency to produce five spurs or double flowers. It cannot be forced, if wanting. It needs no help, only a chance, if present. 4. Some of the new strains are species; some merely varieties. 5. The new species and varieties may be obtained again and again by repeating conditions. 6. Mutation is not mere variation. It is the establishment of a new center, an independent new type. 7. Mutations take place in all directions. The new types may be larger; they may be smaller; they may be stronger; they may be weaker; they may be more brilliantly colored; they may be duller in color; they may be better suited to the life to be led; they may not be so well suited as is the parent species. It is as though the species were sending out colonies, making experiments in all directions.
The theory of mutation is quite in harmony with the observations of gardeners. The parent of Ephraim Bull's Concord grape was a wild grape. Bull simply took care of the sport. John Adlum found the Catawba grape growing wild in the woods of Buncombe County in extreme western North Carolina. It was simply a mutant, a sport. The Clinton arose from a vine planted in the grounds of Professor Noyes of Hamilton College. A number of domestic plums are mutants of wild plums, that is to say, they have not been improved gradually. They have appeared all at once. The Deering gooseberry, to quote Bailey, "is the standard of excellence in American gooseberries, and yet it is only two removes from the wild species." New forms are obtained by crossing or hybridizing, but the leading varieties of our domestic fruits are mutants--voluntary sports--but sports that have been taken care of, and not allowed to be lost.