NATURAL SELECTION OF SPECIES. 163 



the weeds, without being directly attacked, 

 disappear, not because there are no seeds 

 in the soil seeds there are in abundance 

 but because its fertility can now meet 

 the demands of more highly organised 

 plants, and the conditions are in con- 

 sequence unfavourable to lower forms of 

 vegetation. 



The gardener knows that every plant 

 prefers a certain quality and texture of 

 soil, and that it is as impracticable to grow 

 some in rich soil as others in poor. 



In virgin countries beautiful grassy glades 

 may sometimes be seen in a primeval forest, 

 or groups of trees adorning grassy slopes, 

 as in an English park. 



In one locality the soil could provide 

 the sustenance necessary for the more 

 highly organised grass, and it prevailed 

 against forest trees : where the resources 

 were inadequate for grass Nature selected 

 trees. 



When an old forest dies, the trees that 

 naturally replace it are usually of a different 

 species from their predecessors, and some- 

 times new in the locality. The climatic 

 conditions may have remained unchanged, 

 but the timber of the old forest had appro- 

 priated so much of some of the mineral 



