HAVMAKLWi liKCISS. 107 



in type both from the wood land flowers and from the 

 hcd^^crow weeds. Hence tlicir only chance of survival 

 is by exactly adaj)tin^' their. own habits to those of the 

 fo(jd-plants amonj; which they dwell. 



In the bei;innin[i^, no doubt, they varied greatly in 

 their i)eriods of development ; some were earlier and 

 some later. lUit e\ery weed which ripened its seeds t<H> 

 late would naturally be cut down green, s(j as to perish 

 utteny ; while every weed which ripened them too early 

 would stand a fair chance of having thejn buried beneath 

 a whole sod's thickness of ploughed land. Thus onl)- 

 those which happened exactly to tally in time with the 

 corn or the grasses would succeed on an average in keep- 

 ing their position ; so that at last the farmer often posi- 

 tively .sows corn-cockles and thistles broadcast with the 

 grain that he scatters on his fields. They go with the 

 seeds to America and Australia, and they live down the 

 native plants in New Zealand or the Cape Colony. 

 What w^e see in this illustrative example of their seeding 

 is equally true in all their other peculiarities. They 

 have been compelled to adapt themselves to the new 

 conditions by such a stringent selection as seldom or 

 never occurs in natural circumstances. Prairie-fires or 

 inundations take place once in an age, on a single spot 

 at least ; but the annual ploughing of the fields does 

 almost as much every year as these catastrophes can 

 accomplish in a whole century. Indeed, no form of 

 selection is really so severe as that thus unconsciously 

 exercised by man. And when we remember that he 

 has tilled and reaped cereal grains ever since the days 

 when he ground his flint hatchets beneath the primaeval 

 beech-forests of prehistoric Europe, it is not surprisin^T 



