2 INTRODUCTORY [chap. 



value. Farmyard manure is the typical "manure"; 

 marl or chalk would no lonjjcr be regarded as manure, 

 because they do not feed the plant directly; while 

 substances like basic slag or nitrate of soda, which 

 simply supply one or other clement in the nutrition 

 of a plant, should be termed "fertilisers" rather than 

 artificial manures. The distinction is not, however, 

 ver>* clearly drawn, and manure and fertili-^cr are gener- 

 ally and unconsciously used as interchangeable terms, 

 as indeed they will be in this book. 



It is impossible to a^sijjn a period to the discovery 

 of the fertilising properties of the excrement of animals : 

 agriculture must be almost coeval with the human race ; 

 and that tissue of cxjx'ricnce and observation which 

 reaches us as the tradition of farming — the stock-in- 

 trade of the practical man— began to form long before 

 letters existed by which it could be recorded. At any 

 rate, when in Roman times we began to get some 

 record of agricultural practices, we find that not only 

 was the value of dung recognised, but that the virtues 

 of certain other manures, such as marl, had been 

 established. Kven the fertilising effect of a crop of 

 vetches or lupins upon the succeeding wheat crop was 

 sufficiently well known to be related, not only by pro- 

 fessed agricultural writers like Varro and Columella, but 

 also by a poet like Virgil. But to whatever point the 

 knowledge of manures had reached in the time of the 

 Romans, for a long time it made no further advances 

 and bade fair to be utterly lost with the irruption of 

 the barbarians. When the new peoples emerge again 

 in EurOj)e, .iftcr the great movements of the races, we 

 mostly tlnd them practising the Germanic common 

 field system of agriculture, with its rotation of wheat, 

 beans or barie\-, and fallow, followed up by general 

 grazing over the whole area — a system which lends no 



