94 CULTURE OF FARM CROPS. 



very carefully prepared, so as to have a deeper tilth and 

 more uniform depth than that for winter-sown." 



5. " Tkrowing-out " of the Wheat Plant, Before dis- 

 cussing the subject of the habit of growth, in its early 

 stages, of the wheat plant, it will be useful to give here a 

 resume of what Professor Buckman says on the subject of 

 the lifting action of frost on wheat plants, commonly called 

 throwing-out. The changes to which soils, remarkably 

 varied as they are in texture, &c., &e., are subject under 

 atmospheric influences, are most commonly 1. Pulverisa- 

 tion and expansion after frost ; 2. baking after rain ; 3. 

 Compression when filled with moisture; 4. Cracking in 

 drought. Some soils are so loose that heavy winds shift 

 them along with their sustained crops; this is more espe- 

 cially, if not wholly, the case with soils resulting from the 

 disintegration of the more silicious bed of the new red 

 sandstone. The evil may be remedied by giving a more 

 tenacious stability to them, by mixing them with marl. 

 It is a curious disposition of circumstances, that in districts 

 where this soil is met with, stiff kuper marls of the same 

 formation are also met with. In Worcestershire, as pointed 

 out by Professor Buckman, the marl forms rounded knolls, 

 from which it can be carted easily downhill to the light 

 lands. The expansion of soils takes place very generally 

 in "clunchy" clays, all marls having much lime and ar^ 

 gillaceous matter in their composition, with a comparatively 

 small proportion of sand. In soils of this nature the frost 

 penetrates, and by expansion lifts the masses upwards in a 

 remarkable degree. The soils in the Chalk and the Oolites 

 are sometimes very liable to this expanding and lifting ac- 

 tion so much, that the wheat plants growing on them are 

 frequently lifted out and left unplanted after the soil is 

 rendered more solid by succeeding rains. Heavy rains get 

 rid of this to some extent, by working the soil round and 

 down upon the roots of the plants, and even to such an 

 extent as to produce a skin or pellicle on the upper surface. 

 Eolling and sheep-treading are also beneficial in such cases. 

 But where this artificial consolidation is given to upraised 



