Read it through once

Thus our grasslands in Britain are unnatural and artificial productions. If the field drains are choked, moss or fog and rushes appear. Still more interesting, however, is what happens if the farmer is not careful to destroy the taller weeds, such as Dock, Ragweed, Cow Parsnip, Thistles, and the like. If you walk over a grass-field in early spring, you are sure to see some of these pests. At this stage they have a very humble, weak, and innocent appearance: they are quite small rosettes or tufts. Yet they are crowded with leaves, which are hard at work busily manufacturing food material. Soon they begin to shoot up. Their leaves overreach all the neighbouring grasses. Their roots spread in every direction, taking what ought to go to the "good green herb intended for the service of man." They finally accomplish their wickedness by producing thousands of seeds, which are scattered broadcast over the fields.