This is from the Simple Tractors website.
"In 1939, the first riding tractor appeared, which was a walker with a sulky attachment. In the mid-1950痴 the first riding lawn mowers appeared. The "Wonderboy" rear engine models stayed in the line up through the 1970痴, eventually becoming the Coronet, which is still made. The first 4 wheel garden tractor was the 7 horsepower Wonderboy 700, introduced in 1959. In order to avoid confusion with the rear engine models, this tractor became simply the 700 for 1960. In 1961 a slightly more powerful engine was installed and it became the 7.25 horsepower 725. The 725, with yellow paint and minor sheet metal changes, became the Allis-Chalmers B-1. During the rest of the 1960痴 the tractor line was greatly expanded. The 725 evolved into the 9 horsepower Landlord in 1963 and the 10 horsepower Landlord 101 in 1965. The 12 horsepower Sovereign was introduced in 1966. New squared off hoods appeared in 1967. The hoods became rounded with the 3300 series of 1970 and 3400 series of 1972. In 1974 the 7000 series was introduced, being superseded by the 7100 series in 1979. The 7100 series evolved into the Sovereign, which sadly, was discontinued in June of 2000, thus ending over 40 years production of the same basic design."
