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Fig. 18. Explosive seeds and fruits. 1, 2, sage; 3, 4, 5, 6, 7, 8, a kind of mint (Teucrium); 9, horse mint (Monarda fistulosa); Io and 11, “seed” of a smartweed (Polygonum virginianum). (Kerner.)
were found night-flowering catchfly, corn cockle, and bull "thistle.
Grain Seed.—The wild oats is frequently scattered with oats, but there is little of this weed in Iowa except in a few counties in northern and northwestern parts. Mustard is also frequently scattered with oats. There is some danger of scattering quack grass seed with oats. Quack grass seed found maturing with oats will germinate. In one case 8 per cent. of the seed was capable of producing new plants. In an investigation of quack grass in northern Iowa and Minnesota it was found that it is nearly always scattered near the grain elevators. . Straw is an
Fig. 19. Seeds distributed with wheat seed; a and b, wheat; d and e, cockle; c, common chess. (U. S. Dept. Agri.)
important factor in scattering quack grass. A single farm has been responsible for scattering quack grass along the highway in every direction leading from the farm. The straw, with its seed of quack grass, fell along the roadside, and in a few years quack grass was observed along the highway. One farmer said the quack grass was introduced on his farm by using oat straw for covering his grapes. Many other similar cases are on record. Cockle, cowherb and vetch are frequently scattered with wheat seed.
Garden Seed and Ornamental Plants.-Shoofly, which has been widely cultivated as an ornamental plant in this state, has scattered to the fields and has become a troublesome weed in grain fields. Mexican fireweed, cultivated as an ornamental plant, is becoming troublesome in many places. Butter-and-eggs was not only introduced as an ornamental plant and cultivated, but since has spread because sent out with horticultural plants. The bouncing bet, used as an ornamental plant, has become troublesome in northwestern Iowa along the roadsides and in fields. Other plants, as horseradish and ground-ivy, have become weeds in the same way. Railways.-Some railways are Fig. 20. Russian using various kinds of screenings to thistle, distributed sow along their right of way to cover go”. (C. M. the steep fills. A variety of weeds may be found here. Other weeds are scattered from passing cars. Russian thistle, buckhorn, ox-eye daisy, thistle, and other varieties of weeds may be found along the right-of-way. On a patch of ground of not more than two square rods in extent in a town in Central Iowa, in August. 1908, the following weeds were observed by Miss Kellogg: Wild Fig. 21. Kinghead morning glory, hedge bindweed, or agweed distribut- prickly lettuce, sow thistle, pigweed, ed with grain. (C. - 1. lamb's quarter, purslane, velvet weed, King.) mallow, chickweed, shepherd's purse, sweet clover, burdock, curled dock, sheep sorrel, horseweed, pepper grass, wild-radish, black bindweed, water pepper, smartweed, milkweed, black mustard, ragweed, dog-fennel, mullein, creeping Charley, five-finger, Fig. 22. Foxtail. squirrel-tail grass, sandbur, yellow (C. M. King.) foxtail, sedge, wire grass, and horse
1) ISPERSAL OF WEED SEEDS 25
tail. It is but fair to say that these weeds were mostly on soil that had been brought in by the railway company for the purpose of raising the grade of the road bed. Many of these weeds
Fig. 23. Plantain. Fig. 24. Two kinds of
have, however, in the course of five years, spread to the surrounding territory, and the problem of eradicating them has already become serious. Highways.-Highways are an important factor in the distribution of weeds to adjacent fields. No matter how clean the fields are kept, if the seeds of plants like the
cocklebur, Canada thistle, sweet clover, thistle, ragweed, and squirrel-tail grass are permitted to develop and mature along the highways they will naturally spread to the adjacent fields. Vehicles passing from a field infected with weeds, especially when the roads are moist, are sure to leave weed seeds along the roadsides. Then the driving of cattle, and the carrying of grain, all contribute to the weeds that are found along the roadsides, and to the scattering of the same. The following is a partial list of weeds commonly found along the roadside: Poison ivy, horse-radish, horseweed, bull thistle, sweet clover, squirrel-tail grass, Russian thistle, tumbling mustard, cockleFig. 26, 13.14.9anada bur, mustard, large ragweed, small thistle. (C. M. King.) ragweed, foxtail, crab grass, partridge pea, wild blackberry, burdock, wild morning glory, milkweed, velvet leaf, and wild parsnip.