334 



INTRODUCTION TO BOTANY 



Any very prevalent and troublesome weed will usually be 

 found to possess a considerable number of the qualities just 

 stated. A good example of this is found in the common son-el 

 (fig. 241). It is rapidly propagated by its creeping roots, which 

 may form a network throughout a piece of ground nine feet in 

 diameter. As these roots form buds at short intervals, a single 

 plant, when let alone, will soon become the center of a colony. 

 Sorrel also seeds abundantly, and its seeds 

 occur mixed with commercial grass seed and 

 clover seed. It is little affected by drought or 

 frost and nourishes in poor, thin soils, so that 

 neglected pastures often become overrun with 

 it. This sorrel, then, is a good example of the 

 kind of weed that finds its way where the con- 

 ditions are not very fav- 



are 



orable to the growth of 

 more robust plants, and 

 that makes considerable 

 headway beneath the shade 

 of crops taller than itself. 



An example of the oppo- 

 site type of weed, that can- 

 not reach anything like its 

 full size except in deep, 

 rich ground, is the common 

 ragweed (fig. 242). Under 

 favorable conditions this 

 grows so large as to crowd out other plants. It cannot repro- 

 duce itself except by seed, but the seeds are abundant (often 

 more than 20,000 in number) ; the seedlings soon become 

 stout and branching, with a deep taproot which robs all 

 neighboring plants of water and food materials. Other familiar 

 weeds of rich ground with the robust habit of the ragweed are 

 pigweeds ( Chenopodium) of several species, two or three species 

 of rough pigweeds {Amaranthus}, several kinds of dock, the 

 Indian mallow or butter print (Abutilori), and sunflowers. 



FIG. 241. Portion of a plant of the 

 common sorrel 



The leaf is drawn about one half natural 



size. The running roots of a large specimen 



would be at least sixty times as long as the 



piece here shown 



