Arable Land 



But even when the land was made and cleared, and 

 placed under crops, new difficulties began to appear. In 

 most places the soil was utterly exhausted after three or 

 four years under wheat or some other cereal. 



This, however, is not always the case, for in the 

 Rothamstedt Reports one finds that one of the plots 

 which was never manured had grown wheat regularly for 

 sixty-one years, and even then yielded thirteen bushels 

 per acre. Cases have been recorded in New Zealand of 

 continuous high yields of wheat on the same land. 



But that is most unusual, for even on the richest virgin 

 soil the tendency is always for the corn to become less 

 and less productive, whilst weeds increase and flourish 

 so vigorously that they eventually kill it out altogether. 



In an ancient, prehistoric lake village in Italy, weeds 

 were found amongst the villagers' corn, and it is even 

 supposed that they got their seed from Egypt, for one of 

 these weeds is an Egyptian and not an Italian plant. 



The origin of our common weeds is a very difficult 

 question to solve. Some are quite unknown in a wild 

 state, and their original wild ancestor has probably died 

 out altogether, as, for instance, Lamium_amplexicaule. 

 Others are found both as weeds and as, e.g., woodland 

 plants. This is the case with Lamium album, whose 

 range as a weed is far outside its range as a wood plant. 1 

 Some weeds certainly come from warmer and drier 

 countries, but, as has been already shown (see p. 95), 

 many of them are almost cosmopolitan and may have 

 come into existence anywhere. 



On the bare soil which primitive man had prepared 

 for his crops, almost any wild plant would grow, and 

 would find the position much more comfortable than its 

 ordinary habitat. 



To-day we find plants of the South, such as Linaria 

 minor, doing very well on the dry cinders of railway lines, 



254 



