Roots.—Roots, such as potatoes which flower uncertainly and mangolds whose varieties freely intercross in the field, are diffi cult subjects. But mangolds and swedes have yielded to that sys tematic patience which has done so much in Danish agriculture. Helweg, in Denmark, first made clear that the only sound basis of estimation for mangolds was yield of solid matter per acre and not mere wet bulk. Next he demonstrated that different forms or strains within any one variety might be widely divergent in gross yield and percentage of solid matter. Indeed, two strains of the same variety might correspond to a difference of L6 to L8 in value of feeding material from one acre. The best strains were picked out, and by persistent teaching all bad strains were forced out of cultivation; good seed was ensured, and roots came to have a greater feeding value per acre than corn. In Denmark the area under roots has steadily grown, and when the World War stopped the importation of feeding-stuffs it was roots that saved Den mark. There was a time when wart disease (Synchytrium endo bioticum) appeared to threaten wholesale destruction of British potato crops. But steady production of immune varieties, rein
forced by appropriate legislation, may now be said to have brought security to the one great crop in which this country is still self -supporting.