THE SURVIVAL OF THE FITTEST 383 



in our grounds and fields that are quite tender and 

 are occasionally frozen to the ground but which 

 seem nevertheless to be very much at home and 

 are firmly established. Among these is the com- 

 mon beggar's tick {Bidens leticantha) which is so 

 tender that the least frost cuts it badly. Our 

 yellow elder {Tecoma stans) and the common guava 

 have both become completely naturalized, but 

 they are sometimes killed by freezing. No doubt 

 these all find the environment generally congenial 

 and in spite of being seriously injured now and 

 then they are able to maintain themselves. 



Along the roadsides is a common weed, a native 

 of India (JSporobolus indicus) which takes the 

 place of the northern plantains, as it flourishes 

 best in much trodden places. It is a tough, wiry 

 grass and though it does not bear a bur it is very 

 persistent, driving out other plants wherever it 

 becomes established. 



In an early day in Illinois, my native State, the 

 prairies were covered with beautiful flowering 

 plants and nutritious grasses but as soon as settle- 

 ments were made a great variety of weeds came 

 in and began to take possession of the roadsides, 

 yards, and waste places until it seemed as though 



