162 A NEW THEORY OF EVOLUTION. 



ing and instructive is a series of plots 

 showing the effects of different manures on 

 pastures of mixed grasses. 



The plots were differently manured for 

 many years, the same manure being con- 

 tinuously applied to each, but they were 

 neither cultivated nor artificially seeded, yet 

 in the course of years the proportions of the 

 various grasses in the several plots have 

 greatly changed. Where manure, chiefly of 

 a stimulating character, had been applied, 

 the coarse, rank, innutritions grasses have 

 largely increased ; and where another kind 

 enriched the soil principally with mineral 

 food, the fine, highly nutritive grasses have 

 prevailed and ousted the coarser and ranker 

 varieties, although the latter are in appear- 

 ance more robust. 



Success in farming is largely based on this 

 principle of natural selection, and its opera- 

 tion is very noticeable in bringing an ex- 

 hausted farm, overrun by weeds, into a high 

 condition of fertility. 



So long as the farm remains poor in con- 

 dition the weeds cannot be eradicated, 

 because the land does not contain subsist- 

 ence for anything better. But when the 

 resources of the soil are sufficiently rein- 

 forced to produce a good crop of cereals, 



