MR. L AWES' EXPERIMENTS. 23 



red clover, when the land becomes clover-sick 

 it was found that no manure could be relied on 

 to secure a crop, and continuous crops of it are 

 therefore impossible. Experiments on the 

 various root- crops were continued for series of 

 years, and the result published ; also on sugar- 

 beet ; and in 1 876 a commencement was made with 

 potatoes. His experiments on the corn crops 

 go on without cessation. In 1856 an important 

 series of experiments was commenced on grass- 

 land, which, with very little change on each of 

 the twenty plots, has been continued to the 

 present time. The average of the past twenty 

 years shows that the natural produce may be 

 doubled, and even trebled, by the continuous 

 use of special manures. Seeing that nearly 

 two-thirds of the cultivated area of this country, 

 and all the uncultivated, are in grass, this series 

 of experiments is of very great interest and 

 value. 



After thirty-three successive wheat crops Some of 



their 



it is not surprising that the soil begins to ex- special 



lessons. 



hibit symptoms of exhaustion. The rotation 

 experiments show that this may be corrected 



