194 THE SURVIVAL OF THE UNLIKE . [vill. 



ties, it would speedily result in the disbandment of the 

 army ; but my purpose is to discuss the weed rather 

 than the soldier. 



Two great problems are hereby brought directl>' 

 before us: We must determine, in \\h- first pla<'e, why 

 it is that the weed has spread with such virulent ra- 

 pidity, and what are the most effective means of cheek- 

 ing it; and we must then inquire how far it is the busi- 

 ness of the government to interfere. 



Weeds, like other plants, grow where they can find 

 room ; and the more room anj' plant can find, other 

 things being the same, the farther and more rapidly will 

 it spread over the earth. But room, used in this con- 

 nection, does not mean, entirely, space vacant of other 

 plants, but rather conditions of competition into which 

 the given plant can fit itself with prosperity. Ground 

 may be covered witlj a given plant, and yet a species of 

 wholly different character and habits may thrive along 

 with it. This is well illustrated in the growth of twin- 

 ing or climbing vines in dense thickets of shrubbery, or 

 the practice, common even with the Indians, of growing 

 pumpkins in corn fields. If weeds, then, are to be kept 

 out of grounds, the land must not only be occupied with 

 some crop, but with a crop which will not allow the 

 weed to grow along with it. In practice, it is impos- 

 sible to select all crops from plants which so completely 

 encumber the ground that no intruder can find a foot- 

 hold; but this disadvantage is readily and almost wholly 

 overcome by means of the rotation of crops, — one crop 

 in the rotation destroying what weeds may have crept 

 in with the preceding ones. Thorough cropping of the 

 land and judicious rotations of crops, therefore, are 

 conditions against which no weeds can stand; and as 



