The crop-grower necessarily introduces the condition of a bare soil for a portion of the year for every crop, and must therefore accept the situation: while he invites their presence and development, even stimulating them in various ways by making the conditions favorable for the growth of his crop plant, he must become a competitor with the weeds for the possession of the soil. The weed seeds are either in the soil or soon find an abundant entrance, and if the way is clear the young pests are up and doing as with the morning sun.
Most of our weeds, like much of our vermin, have come to us from beyond the sea. Just how they emigrate in every case will never be known; some came as legitimate freight, but many were "stowaways." Some entered from border lands upon the wings of the wind, on river bosoms, in the stomachs of migrating birds, clinging to hairs of passing animals, and a hundred other ways besides by man himself. Into the New England soil and that south along the Atlantic seaboard the weed seeds first took root. Also the native plants, with a strong weedy nature, developed into pests of the farm and garden. Many of the native weeds are shy and harmless in comparison with the persistent and pugnacious ones that have like vagabonds emigrated to our shores. Why should it be that plants of another country not only find their way here, but after arriving assert themselves with a vigor far surpassing our native herbs? Dr. Gray, in writing upon this point, says, "As the district here in which the weeds of the Old World prevail was naturally forest-clad, there were few of its native herbs which, if they could bear the exposure at all, were capable of competition in the cleared land with emigrants from the Old World." The European weeds had through long ages adapted themselves to the change from forest to cleared land, and were therefore prepared to flourish here in the rich forest soil that was suddenly exposed to the sun and subjected to other new conditions by the felling of the trees. To go back of this we are not sure that the ancestors of some of our European weeds ever came from the forests, but instead were brought into the cleared-up lands from open regions in the early days of agriculture in the Old World. As civilized man moved westward, the weeds followed him, re-enforced by new native ones that soon vied with those of foreign blood. Not satisfied with this, these natives of the interior ran back upon the trail and became new enemies to the older parts of our land. The conditions favorable for the spreading of weeds have increased with the development of our country, until now we are literally overrun. Weeds usually as seeds, go and come in all directions, no less as tramps catching a ride upon each passing freight train than in cherished bouquets gathered between stations and tenderly cared
