The Roots of the Wheat Plant. 189 



a. Pulverization and Expansion after Frost. 

 h. Caking after rain. 



c. Compression when filled with moisture. 



d. Cracking in drought. 



a. Some soils hold together with so little tenacity as to be 

 shifted about by heavy winds with their crops upon them : this is 

 often the case with soils 

 made from the disinte- 

 gration of the more silici- 

 ous beds of the new red « 

 sandstone, an evil which 



can be prevented by a Diagram 9.-Section of Xew Red Sandstone. 



, 1 • r 1 "' Sandstones. 6, Keuper marl. 



neavy dressmg ol the 



stiffer keuper marls of the same formation, which are usually not 

 far removed from the sand, often forming the rounded knolls in 

 Worcestershire, from whence the hauling is usually down hill 

 with the load. These marls were formerly much used as a manure, 

 but as they are found to contain no active principles, marling has 

 been discontinued, but it might still be well to employ it as 

 above as an ameliorator. 



Expansion, which causes the lifting action, takes place very 

 generally in clunchy clays and marls containing much lime and 

 argillaceous matter with but a comparatively small admixture of 

 sand. Frost penetrates into its intestines and by its expansion 

 in thawing crumbles the land to such an extent that it occupies 

 a much greater space than it did in its more solid condition, and 

 hence the lifting action by expansion. Some of the soils on the 

 chalks and oolites are liable to this, and the result is that the 

 wheat-plant is frequently lifted out of its place and left unplanted 

 after the rains have once again rendered the soil more solid in its 

 texture. This tendency is much mitigated in the winter wheat by 

 tilth ploughing when after turnips, and here less pulverization is 

 necessary : much more, however, after seeds, unless the land be 

 tolerably free from weeds ; but, on the other hand, the roots of 

 seeds j)rcvent lifting to a consldcra'ole extent. 



Much of the injury from lifting is often prevented by the 

 heavy rains by which frost is sometimes succeeded, which causes 

 the soil to work down again around the roots, and in dry weather 

 even to form a pellicle on the surface : this action may be greatly 

 assisted by rolling, or, as is sometimes done, by sheep-treading in 

 March, to l)e followed, however, by hoeing and top-dressing, in order 

 to loosen "the soil, and thus expose it with its chemical matters 

 to the acticm of the atmosphere at the time of accelerated growth. 

 The best method which I have observed to obviate the lifting 

 tendency in soils liable to it is to get as large root crops as ])os- 

 siblc, ; nd always leave the leaves to be ploughed in. This ulti- 



