EARLY SEEDTIME. 87 



not let them drop out upon the ground just underneath 

 their own branches ? For the very same reason that the 

 farmer does not crop the same land with corn or turnips 

 ten years running. The plants had unconsciously dis- 

 covered rotation of crops ages before the agriculturists 

 consciously hit upon it. A weed cannot grow over and 

 over again in the same place, any more than flax or 

 horse-beans ; it soon uses up the soil, which must then 

 lie fallow a little, or else bear some less exhausting 

 plant that is to say, some plant that does not drain it 

 of the same materials as its last occupant. Hence those 

 wild things which happened to show any tendency 

 towards dispersive devices have outrun all others in the 

 struggle for existence ; indeed, dispersion in some form 

 or other has become an absolute necessity for every kind 

 of plant in a state of nature. Some of them manage it 

 by producing tubers side by side with the decayed ones, 

 like the orchids ; others send out runners or suckers like 

 the strawberry and the creeping buttercup ; yet others 

 sprout afresh here and there from underground stocks 

 or reserve stores, like coltsfoot or potatoes. But by far 

 the greater number manage to get their seeds scattered 

 for them either by the wind or by means of animals : 

 for these two main motor powers of the environment are 

 always utilised for every purpose by plants, whose own 

 powers of locomotion are so very feeble. Sometimes 

 the seeds stick, like burrs and cleavers, to the wool of 

 sheep or the hair of animals, and are rubbed off at last 

 against a hedge or a post, at a distance from the mother- 

 plant. Sometimes they are swallowed whole but not 

 digested, as in the strawberry, raspberry, and cherry. 

 Sometimes they are carried before the wind by expanded 



