V] RAISING OF THE FERTILITY LIMIT 65 



distinction is recognised both by custom and by law : 

 the maintenance of fertility between the natural 

 limits is regarded as the tenant's business, while the 

 extension of the upper limit is considered to be the 

 landlord's duty. 



Over the greater part of England such an exten- 

 sion of the fertility limit has taken place. Often 

 indeed the extension was necessary before the adop- 

 tion of expensive modern methods of farming could 

 be justified. The process has generally involved some 

 conflict with natural conditions, and the new order of 

 things stands only so long as constant care is exercised. 

 In most cases the original condition is resumed if the 

 intervention of man ceases for a time ; a plot of land 

 at Rothamsted that has been left to itself since 1882 

 is now a dense thicket and bids fair to become an 

 impenetrable wood before long. But the expenditure 

 necessary to maintain the new limit is much less than 

 that required to reach it, so that in this sense the 

 improvement is entitled to be called permanent. 



Some of the land of England has always been 

 open gi'ass-covered Down land, and this was inhabited 

 even in prehistoric times. Much of the land, however, 

 was covered with forest which had to be cleared away 

 before fields could be made but which would, as the 

 Rothamsted experiment shows, soon spring up again 

 if the suppressing hand of man were removed. It is 

 difficult for us now to realise the magnitude of the 



