334 INTRODUCTION TO BOTANY 
Any very prevalent and troublesome weed will usually be 
found to possess a great many of the qualities just stated. A 
good example of this is found in the common sorrel (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 flourishes 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- 
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, 
The leaf is drawn about one half natural —. 7 
size. The running roots of a large specimen rich ground, is the common 
would be at least sixty times as long as the ragweed (fig. 242), Under 
piece here shown ine , 
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 (Adutilon), and sunflowers. 
Fig. 241. Portion of a plant of the 
common sorrel 
