Even more curious that a useful service, which has a magnet in agriculture, helping farmers to purify the seeds of cultivated plants from weed seeds. Weeds have hairy seeds clinging to the fur of passing animals and because of this extends far from the mother plant. This feature of weeds, produced in their millions of years of struggle for existence, used agricultural machinery, in order to separate using the magnet rough weed seeds from smooth seeds such useful plants as flax, clover, alfalfa. If clogged seeds of cultivated plants sprinkle iron powder, the grains of iron firmly stuck to the seeds of weeds, but will not stick to a smooth seeds of useful plants. Getting in the action of a sufficiently strong electromagnet, a mixture of seeds will automatically be split into pure seeds and foreign material: magnet catches from a mixture of all those seeds that are covered with iron filings.