Water-soluble copolymers having a K value of from 15 to 120 (determined according to H. Fikentscher in an aqueous solution of their sodium salt at 25.degree. C., a pH of 7 and a polymer concentration of the Na salt of 1% by weight) contain, in polymerized form,(a) not less than 80 mol % of one or more monoethylenically unsaturated C.sub.3 -C.sub.6 -monocarboxylic acids,(b) from 0.5 to 20 mol % of a comonomer which possesses two or more ethylenically unsaturated, non-conjugated double bonds and one or more --CO--OX groups and/or their salt with an alkali metal, ammonium or alkaline earth metal base, and, if required,(c) not more than 10 mol % of one or more comonomers which differ from (b) and possess two or more ethylenically unsaturated, non-conjugated double bonds, and the said copolymers are prepared by copolymerization of the monomers (a), (b) and, if required (c) in aqueous solution and are used for coating seed.