1250. Influence of rotations in destroying insects and weeds. Olivier, member of the Institute of France, has described all the insects, chiefly Tipulï¾µ and Muscï¾µ, which live upon the collar or crown of the roots of the cereal grasses, and he has shown that they multiply themselves without end, when the same soil presents the same crop for several years in succession, or even crops of analogous species. But when a crop intervenes on which these insects cannot live, the whole race perish for want of proper nourishment for their larvï¾µ. (Mem. de la Societe Royale et Centrale d'Agr. de Paris, vol. vii.) Rotation is also of great value in enabling the farmer more completely to eradicate and destroy those weeds which constantly spring up in cultivated lands.