HOW WEEDS SPREAD 501 



692. Animals. Wild and domestic animals both aid in 

 carrying weeds from place to place. Some weed seeds are 

 provided with hooks which cling to the wool or hair, as the 

 cocklebur, burdock, and beggar's-ticks. Others are stored 

 as food by animals or by birds and are forgotten, springing 

 up as plants in new locations the following year. Ground 

 squirrels, prairie dogs, and other burrowing animals store 

 large quantities of grass and weed seeds, not all of which are 

 consumed, and some of which are not buried so deeply that 

 they fail to grow. Weed seeds are eaten by birds, carried 

 by them for long distances, and then, passing through their 

 digestive systems unharmed, are dropped in new localities. 

 Branches of weeds bearing seeds may be used by birds or 

 animals in building nests and thus disseminated. The 

 droppings of live stock furnish a local means of distribution 

 from one field of the farm to another when animals are 

 changed from pasture to pasture or worked in the field. 



693. The Activities of Man. Human operations furnish 

 many of the methods of weed distribution, some of which are 

 hardest to counteract. Vehicles along roads or from fields 

 often, particularly in damp weather, carry seed in the mud 

 which sticks to them. Tillage implements and the work of 

 tillage furnish another means of distribution. Weed seeds 

 or the weeds themselves may be carried from place to place 

 on the implements, or may be moved with the movement of 

 earth in tillage. Roots of perennial weeds are often carried 

 by tillage tools; for this reason, poor or occasional cultiva- 

 tion of fields infested with quack grass, Johnson grass, or 

 weeds that spread by similar means is often worse than no 

 cultivation at all. Threshing machinery furnishes a ready 

 means by which weed seeds are carried from farm to farm. 



Railroads are a great agency in the spread of weeds, as 

 they often carry weed seeds long distances in the bedding 

 of cars, in shipments of grain, and in other material. The 

 seeds may drop out along the right of way or be cleaned out 



