384 LUSSOIfS WITB PLANTS 



growths, his field might work into a copse and 

 then into a forest, rather than into a meadow. It 

 is the general tendency in all untilled, unburned, 

 and nngrazed lands to run into forests. 



483. So there is alternation, or rotation. The 

 land tires of unvaried cropping. The longer any 

 plant occupies an area to the comparative exclusion 

 of others, the greater are the chances that another 

 plant will win the victory if the place is again 

 thrown open to settlement. A poplar forest may 

 succeed the pine. 



484. More plants can grow upon any area if 

 they are of diverse kinds than if they are of one 

 kind. An orchard which cannot grow more trees 

 can (and usually does) grow ragweed and docks in 

 abundance. After the land is completely planted 

 to corn, the farmer plants pumpkins between. 

 Meadows of mixed grasses, or grasses and clovers, 

 may give more pounds of hay than those in which 

 there is but a single kind of grass. The intro- , 

 duced weeds and insects which work most havoc 

 are those which are unlike our own plants and in- 

 sects; they thereby find the field open, as men 

 find a "business opening" where there are fewest 

 competitors. That is, by "divergence of character," 

 as Darwin expressed it, plants are able to live to- 

 gether without demanding space in proportion to 

 their numbers. 



