This is not as it ought to be. Even if they are otherwise harmless, the weeds use up a large part of the plant food in the soil, and they rob the young oats of the necessary light and air. In this way weeds prove an expensive crop to the farmer. It pays him to study their life-history so as to learn how they may be eradicated, and to spend some labour in the task of doing so. A common pest in the Orkney cornfields is the “runcho” or “runchic,” known elsewhere by the name of charlock or wild mustard. Its pale-yellow flowers overtop the growing oats, and their unwelcome gleam makes some fields conspicuous for miles around. The form of the flower shows that the charlock belongs to the same family as the turnip and the cabbage and the fragrant wallflower of our gardens. The flower has four petals, and the cross-like arrangement of its six stamens, four long and two short, has given them their name of _Cruciferæ_, or cross-bearers. The seed-vessels, like those of the turnip, are in the form of a long, narrow pod with a partition running down the middle. The seeds are small and hard, and they grow only in a freshly-stirred soil with plenty of light and air. When a field is laid down in grass they make no sign of life, but when it is ploughed for the next crop of oats they spring up once more, and make it as gay as a flower-bed. Two kinds of this plant are found—the one, charlock, of a light yellow colour, common in peaty and clayey ground; and the other, wild mustard, of a deeper yellow, found in sandy soil. [Illustration: _Some common weeds._ 1. False oat grass. 2. Chickweed. 3. Ragwort. 4. Prunella. 5. Wild mustard (_Brassica Sinapis_). 6. Charlock (_Raphanus Raphanistrum_). 7. Corn spurrey. 8. Sheep’s sorrel. 9. Common sorrel.] Another showy weed is the yellow corn-marigold. This handsome flower seems more dainty in its choice of soil, and in some districts it is not common. A glance at the open flower shows its kinship to the “wee, modest, crimson-tipped” daisy. The so-called flower is not one, but a host of tiny flowers or florets growing upon a broad green disc called the receptacle. This compound or composite type of flower is found in a large number of common plants, named on this account _Compositæ_. Many of them are found in Orkney, and they are a very interesting as well as a numerous family. One of the best known is the dandelion, a more beautiful flower than many which we grow in our gardens, and only its abundance prevents our admiring it. If we examine the florets of the dandelion, we see that each of them has a corolla forming a long yellow ribbon on the side farthest from the centre of the flower. In the corn-marigold only the outer florets have this ribbon, which forms a halo of rays round the central portion. In the daisy these rays are white, with the tips pink, especially underneath.