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, ¢.¢., woodland 
plants. This is the case with Lamium album, whose 
range as a weed is far outside its range as a wood plant.’ 
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 
