In 1855 Clark became the gardener at a local boarding school. It was there that he first developed an interest in growing potatoes and became fascinated by the varieties produced by a single root. However, the onset of a life-long heart complaint compelled him to quit this job and take on less arduous gardening work. In the following two seasons Clark saw that one of his new seedlings had survived when other local potato plants had been devastated by blight. He realised that this new variety held great promise, so he nurtured them and in the spring of 1874 he sent some of his seedlings to the noted horticulturist
Shirley Hibberd for him to test at his trial-ground in
Hornsey. Hibberd's tests confirmed the robust good qualities of the new variety and he recommended it to seed merchants
Messrs Sutton & Son of
Reading, who purchased Clark's entire stock and released it to the public as Sutton's Magnum Bonum in 1876. Magnum Bonum indeed proved to be a commercial success and soon became the best-selling variety grown in Great Britain. Its ability to survive hard frosts recommended it to Scottish growers in particular. It was a white, kidney-shaped late maincrop with a floury texture and a blandly sweet flavour that grew vigorously, withstood disease, and gave good yields. In 1880, reporting on the 7th annual Potato Show held at the
Crystal Palace,
The Times said: "To ascertain and announce which is the most serviceable potato would be a great national service. There is a very considerable consensus of opinion that in a great number of soils Messrs. Sutton's 'Magnum Bonum' has survived in bad years, and yielded abundantly in good. It is a recent introduction, and the breeder who first raised it in 1871, Mr. Clark, of Christchurch, was present yesterday at the show. It has been supplied to the Marquis of Lansdowne and other landed proprietors in Ireland, and to one of the Dublin relief funds, and is stated to have answered admirably in the humid soil of Ireland." The popularity of Magnum Bonum peaked in about 1890, after which it degenerated and became susceptible to blight. Nevertheless, it was used to breed numerous other disease-resistant varieties. Clark subsequently produced a number of other varieties released by Sutton & Son. These included Maincrop/Langworthy (1876), Reading Hero (1881), Sutton's Seedling (1886), Abundance (1886), Best of All (1887), Satisfaction (1887), Masterpiece (1887), White Kidney (1888), Early Market (1888), Matchless (1889), Nonesuch (1889), Perfection (1892), Triumph (1892), Supreme (1893), Epicure (1897), No Plus Ultra (1897), Reliance (1897), Ninetyfold (1897), Ideal (1898), Inevitable (1898), Centenary (1900), and Favourite (1902). Of these, Ninetyfold was a successful variety that was grown commercially until the 1960s and Epicure proved an outstanding variety that is still grown today. James Clark died at his Christchurch home on 5 June 1890 aged 65 years. ==References==