Men watched the natural pastures where cattle get fat on the wild grass, as they do in the Fens, and many other parts of England.

And then they saved the seeds of those fattening wild grasses, and sowed them in fresh spots.
Often they made mistakes.

They were careless, and got weeds among the seed--like the buttercups, which do so much harm to this pasture.

Or they sowed on soil which would not suit the seed, and it died.

But at last, after many failures, they have grown so careful and so clever, that you may send to certain shops, saying what sort of soil yours is, and they will send you just the seeds which will grow there, and no other; and then you have a good pasture for as long as you choose to keep it good.
And how is it kept good?
Look at all those loads of hay, which are being carried off the field.