The _O. sativa bifera_ is but a variety of the _O. sativa_, as by long continuance of growth from the same seed in this country it reverts to the common form; and hence the giant sort should be frequently renewed from an imported stock. Sainfoin has been much cultivated on calcareous soils, more especially on the free-stones of the oolite rocks, and on the chalk, off which formations it is scarcely known, except on some calcareous sands in the eastern counties. In the limestone and chalk districts sainfoin is grown as a permanent crop, and formerly lasted six or eight years. In the eastern counties the little there grown is by way of a shifting crop, in the same place and manner as common clover. The permanency of sainfoin is yearly becoming greatly diminished from the circumstance that its seed is so much mixed with that of the burnet, _Poterium sanguisorba_, var. _muricata_. To such an extent does this evil occur, that we have examined samples of sainfoin seed in which there were at the rate of from twenty to forty thousand of burnet seed-pods per bushel; and when we consider that these pods have for the most part two ripened seeds, and those of a plant growing so much more rapidly than the sainfoin, we can form some notion how the desired crop is soon smothered and overpowered by the burnet, which at best is but a rank weed, of no agricultural value; for whatever of good there may be in our ordinary native salad burnet, which is a smaller and more succulent plant, this sticky foreign interloper cannot possibly have any claim to our regard. The reason why it has gone on so long unchallenged is that the burnet-seed, though of an entirely different shape from the sainfoin, is somewhat of the same colour; and then in their growth both plants have winged leaves, and the difference between the entire leaflets of the sainfoin and the toothed leaflets of the burnet did not at first strike the farmer; now, however, the difference is better understood, and farmers begin to require that the burnet-seed shall be sifted from the sainfoin. This of course will demand the payment of a better price for the better sample, as in the process of sifting many of the smaller sainfoin seeds go through with the burnet; but this will be well worth a better price, as the larger seeds will undoubtedly tend to produce a better crop. If, however, there should be any doubt about pure sainfoin seed, we should recommend the decorticated seed being used, as in it the burnet could not possibly escape detection. As the history of burnet is so important in connection with the sainfoin crop, it cannot be out of place to introduce the following description of this weed:—