The influence of this plant on weed destruction when grown for hay is greater than with the other varieties of clover. This is owing in part to the shade resulting from its rapid growth and in part to the two cuttings which are usually made of the crop. These two cuttings prevent the maturing of the seeds in nearly all annual weeds, and to a very great extent in all classes of biennials. The power of this crop to smother out perennials is also considerable, and when this is linked with the weakening caused by the two cuttings, it sometimes proves effective in completely eradicating for the time being this class of weeds. [Illustration: Fig. 2. Medium Red Clover (_Trifolium pratense_) Oregon Experiment Station] =Distribution.=--Medium red clover is thought to be native to Europe. It was probably introduced into England some time early in the seventeenth century. That it was attracting attention about the middle of the century or a little later, is rendered probable by the fact that it is discussed at considerable length in the third edition of Blyth's "Improver Improved," published in 1662, while it is not mentioned in the first edition, published in 1650. It was doubtless introduced into the United States by the early colonists and at sundry times. Medium red clover will grow in good form only in the temperate zone, since it cannot stand excessive heat or excessive cold. The northerly limit of its successful growth in North America is somewhere about 50 deg. north latitude on the wind-swept prairies, but on suitable soils, and protected somewhat by trees and winter snows, it will probably grow 10 degrees further to the north. In British Columbia, on the Pacific slope, it will probably grow as far north as Alaska. But on prairies eastward from the Rocky Mountains, it has not been grown with much success much further north than 48 deg., unless under the eastern shadow of the Rocky Mountains. Low temperatures in winter, where there is only a moderate covering of snow, are far less fatal to clover plants than exposure to the sweep of the cold winds. Even where the thermometer is not so low as in the areas just referred to, such winds are particularly damaging to the plants when they blow fiercely just after a thaw which has removed a previous covering of snow. In some instances, one cold wave under the conditions named has proved fatal to promising crops of clover over extended areas. In a general way, the southerly limit of vigorous and reliable growth may be put at about 37 deg.. But in some localities good crops may be grown further South, especially in some parts of Tennessee. Nor would it be correct to say that medium red clover grows at its best in many localities much south of 38 deg.. On the plateaus it can be grown further South, where the soil is suitable.