VIII.] A SPECIFIC EXAMPLE. 197 



rank patches of Canada thistles are in neglected fields 

 or along roadsides, where there is least competition with 

 vigorous crops and with the cultivator. The roadsides 

 of the western and prairie states are noticeably more 

 weedy than those of the east, where there are less waste 

 grounds in which the weeds multiply and where the 

 roadside turf is usually stronger. All new countries 

 suffer serious incursions of weeds, because the equilib- 

 rium of nature has been broken by removal of forests 

 or breaking up of prairies, and every plant makes an 

 effort, in the resettlement of the land and the recon- 

 struction of competition, to gain a place for itself. The 

 agriculture of a new country is generally one-sided and 

 imperfect, and one crop usually eclipses all others ; and 

 in the absence of rotation, the weeds fill in the chinks, 

 spread themselves into waste and half -cultivated lands, 

 and soon threaten the single-handed agriculture like 

 an invading army. But the older and better tilled the 

 region, the less the farmers know about weeds. 



I recall an excellent example of the invasion of a 

 weed into an unoccupied area. There is a long stretch 

 of sandy drift near a certain village upon the eastern 

 shore of Lake Michigan. In 1880, I found a strange 

 plant in the loose sand. It is one of this very family 

 of pigweeds.* It spread rapidly, and in three years 

 had completely occupied a region three or four miles 

 long, and had begun to encroach upon cultivated fields. 

 I considered it a vile weed, and warned the people 

 against it. But presently other wild plants began to 

 dispute possession of the area, and they set up a back- 

 fire against it. The weed receded, and it is no longer 

 a prominent plant on that shore. Even the Russian 



♦ Corispermum hyssopifolium. 



