INTRODUCTION 9 



long to allow the land to be well worked over, so that no single 

 weed has the opportunity of obtaining such a hold as black 

 bent has on Broadbalk. At the present time, however, the 

 perennial corn sowthistle (Sonchus arvensis] is causing much 

 trouble in Hoos field, as it spreads by underground stems, and 

 the broken pieces left after cultivation shoot up again with the 

 barley. 



In contrast to Broadbalk and Hoos, Barn field is devoted 

 exclusively to root crops. Sugar beet used to be grown, but 

 of late years mangolds have been taken instead. The field is 

 remarkable for the poverty of its weed flora. At no time in 

 the year do a large number of weeds occur, and the variety 

 of species is small. Some chickweed and groundsel, a few 

 creeping thistles and greater plantain, represent the major part 

 of the weed population at any period of the year, and even 

 after the winter, just previous to ploughing, the same thing is 

 seen. The continuous growth of roots for so many years, 

 with the attendant cultivating and hoeing, has cleared the 

 land of most of the weed seeds which may have been 

 originally buried in it, and has also prevented weed colonists 

 from establishing themselves and shedding their seeds. 



Many of the points touched on in this introduction will be 

 dealt with more fully in later chapters, but enough has been 

 said to indicate the vital importance of a right understanding 

 of the weed problem if it is to be approached in such a way as 

 to render profitable assistance to the farmer. With the im- 

 provements in agricultural machinery and the greater applica- 

 tion of chemical knowledge to agriculture in the direction of 

 manures and sprays, it is conceivable that it may be possible 

 at no distant date to hold the weeds far more under control 

 than has ever been the case in the past. 



