12 



the influence of exhaustion, manures, and variations of 

 season, on the development, and on the organic and 

 mineral composition, of the grain and of the straw, 

 respectively; and the results have proved to be of 

 much interest. It will be observed that nitrogen 

 determinations have been made in selected cases up to 

 1881 inclusive, but ash analyses only up to 1871. 

 But, as has been stated, samples of the partially dried 

 produce (grain and straw) of each plot, each year, are 

 preserved for future selection for nitrogen determina- 

 tions or other examination of organic composition, and 

 the ashes are prepared and preserved for future selection 

 for ash analysis, as the progress of exhaustion, or the 

 influence of full supply, may indicate to be desirable. 



3. The Soils of the Continuous Wheat Plots. 



Unfortunately, the conditions of soil-sampling essen- 

 tial to render the analytical results available for the 

 discussion of many important questions, such as that of 

 the soil as a source of the nitrogen of vegetation, and 

 collateral points, which the continuous growth of crops 

 as at Eothamsted suggest, are only learnt by experience, 

 and are perhaps not yet realised anywhere else. Thus, 

 although the Broadbalk field soil was sampled as early 

 as 1846, only a few samples of the surface soil of 

 indefinite area, and of only approximately estimated 

 depth, were taken ; so that no acreage calculations can be 

 founded on the results, and no exact comparison made 

 of the condition of the land at that time, and in subse- 

 quent years, when more careful samples were taken. 



Samples of a definite area and depth were first taken 

 in 1856, but then only of the surface soil, and only 

 from 4 plots ; but from 8 places on each plot, a mixture 

 being made of the 8 samples in each case, and in this 

 mixture the nitrogen (by soda-lime), and the carbon, 

 have been determined. 



In 1865 samples were taken from 11 plots, from 

 8 places on each; and in each case representing the 



