THE WEEDS OF CULTIVATION 87 



of 1250 feet is reached in the Highlands, and in some parts there 

 are traces of former cultivation as high as 1500 feet. A list of 

 weeds in the Wheat zone, and of those in the Oat zone, might be 

 made ; it will be found that some are found at the higher altitude 

 of the Oat belt which are not present in the lower Wheat area. A 

 map, with the height above the sea level marked, could be drawn 

 and the Wheat and Oat fields inserted, and coloured to show the 

 difference in the altitude at which the two crops will grow. 



The effect of farming operations on weeds and their influence 

 on the Plant Associations that occur would form an interesting 

 series of observations from year to year. To get approximately 

 accurate results, it would be necessary to keep records of the 

 ploughing and manuring of the field, the kind of manure given, 

 and the rotation of crops. A complete list of the weeds found 

 each month should be kept and compared from year to year, 

 or from season to season. After four or five years it would be 

 possible to note whether the same weeds occurred year after 

 year, if the same manure was used. Where the crop and the 

 manure vary from year to year, it would seem likely that the 

 constant presence of certain weeds is due to the character of the 

 soil. The presence of certain weeds, year after year, in conse- 

 quence of ploughing operations, would indicate some relation 

 between the life of the plant and the greater depth of soil through 

 which the roots could penetrate ; ploughing, for instance, would 

 probably increase the number of weeds with a deep-rooted system. 

 One result of the constant ploughing to which arable land is natur- 

 ally subjected is, that many of the weeds are annuals ; the weeds 

 of meadows and pastures, undisturbed by the plough, are, as has 

 been stated, perennials. 



The result of leaving ground fallow for a year and its effect 

 on the next crop may be observed. Experiments at Rothamsted 

 on Wheat plots showed that the produce of Wheat after fallow is 

 considerably higher when it is grown continuously, partly owing 

 to the fact that there are fewer weeds. 



The effect of a wet or dry season is best realised by keeping 

 a weather chart, which should show the temperature and the 

 hours of sunshine. These can usually be checked from the records 

 of the meteorologist of the district. The rainfall and degrees of 



