There remains still another type of variability which has been noticed from very early days, and received the name _sport_, because quite suddenly, from a crop of otherwise similar specimens, one or a few plants showed marked and permanently transmitted differences from the average condition. Such sudden offshoots, which occur rather frequently in many plants, are known as mutants, the process as mutation. Hugo de Vries, a Dutch botanist of world-wide fame, was the chief modern figure who drew attention to mutants, and explained how they differ from fluctuating variants in that while these tend to revert to the average or mass conditions the mutant, once it appeared, held true to type. A well-known example of mutation is the cabbage, brussels sprouts, cauliflower, and kohl-rabi, all of which are sports or mutants from a weedy seaside plant of the mustard family, native in Europe. Since their appearance, hundreds of years ago, they have held their essential characters. If they had been environmental variants they would in all probability have reverted to their weedy ancestor. Hundreds of sports or mutants have been recognized and isolated, so that many of our most valuable garden plants have arisen through this ability of plants to vary in often sudden and rather startling degree. The gardener and horticulturist, from long observation and a keen sight for valuable novelties, have always known that sports are fruitful sources of new forms of plants, but De Vries first scientifically studied them and worked out the principles by which they apparently react. The cause of them is still unknown.