8 IVccds. 



weeds, but they are native to the soil, and 

 the number of the species is not only lim- 

 ited, but those which do exist seem unable 

 to multiply to any great extent in the natu- 

 ral surroundings amid which they grow. 

 On the other hand, in lands that have long 

 been cultivated, we frequently find that for- 

 eign varieties of weeds are far more numer- 

 ous and aggressive than the native spe- 

 cies. Regions that have been settled with 

 inhabitants drawn from different countries 

 are peculiarly liable to be infested with the 

 weeds of the various countries from which 

 these inhabitants have come. The seeds of 

 the weeds are imported along wnth the grain 

 that is brought for sowing, and are intro- 

 duced in various other w^ays. Some of the 

 varieties thus imported do not take kindly 

 to the new conditions, but other sorts, like 

 the people who have brought them, often- 

 times find their new surroundings pre-emi- 

 nently favorable to a greatly increased 

 development. 



The ''prevalence of weeds" depends 

 ( I ) on the number of weed species found 

 in any locality; and (2) on the extent to 

 which these various species are allowed to 

 multiply. 



