HOW PLANTS DRINK. 67 



But in nature crops are not, as a rule, removed 

 from the soil ; they die and wither, and return 

 to it for the most part whatever they took from 

 it. The dead birds and insects, and the droppings 

 of animals, are sufficient manure for the native 

 woodland. Still, even in nature, certain plants 

 more or less exhaust the soil of certain valuable 

 materials; and therefore natural selection has 

 secured a sort of roundabout rotation of crops 

 in a way of which I shall have more to say here- 

 after. Many plants, for example, which greatly 

 exhaust the soil, have winged or feathery seeds ; 

 and these seeds are carried by the wind to fresh 

 spots, where they alight and root themselves, in 

 order to escape the exhausted soil in the neigh- 

 bourhood of their mothers. Other plants send 

 out runners, as they are called, on long trailing 

 branches, which root at a distance, and so start 

 fresh lives in unexhausted places. Yet others 

 have tubers, which shift their place from year 

 to year ; or they push forth underground suckers, 

 which become new plants at a distance from the 

 parent. All these are different natural ways for 

 obtaining what is practically rotation of crops ; 

 nature invented that plan millions and millions 

 of years before it was discovered by European 

 farmers. 



Moreover, nature sometimes even goes in for 

 deliberate manuring. Plants like buttercups 

 and daisies, that live in ordinary meadow soils, 

 to be sure, get enough nitrogen and sulphur 

 and other such constituents from the mould 

 in which they are rooted. But in very moist 



