498 OF GREEN OR FALLOW CROPS. 



ence of the oxygen it contains — the exposure of the naked soil to the at- 

 mosphere for a length of time is said by some to be productive of another 

 good effect. The atmosphere contains a small and variable portion of 

 ammonia (p. 156). Of this ammonia, a portion is brought down by the 

 rains and a portion is probably absorbed by the leaves of plants as they 

 spread themselves through the air. But the clay, the oxide of iron, and 

 the organic matter of the soil are supposed also to have the power of 

 extracting this ammonia from the atmosphere and retaining it in their 

 pores. If so, the more the soil is exposed, and for the longer period 

 to the air, the more of this substance will it extract and absorb. If 

 turned over by frequent ploughing, it will be able to drink it in more 

 abundantly, from the greater surface it can present to the passing winds; 

 and if, besides, it be kept naked for an entire year, a still larger accumu- 

 lation must take place. And as this ammonia is known in many cases 

 to be favourable in a high degree to the growth of plants, it is not im- 

 reasonable to believe that if thus absorbed in quantity from the air, it should 

 be one source at least of the augmented fertility of fallowed land. 



To one or other — or to all of these causes combined — the acknowledged 

 benefit of naked fallows is in a great degree to be ascribed. 



0[ green or fallow crops little need be said in addition to what I have 

 already laid before you in reference to the rotation of crops. The green 

 crop demands a comparatively small supply only of those inorganic sub- 

 stances which the corn crops specially require. During its growth, 

 therefore, these latter accumulate in the same way, though in a some- 

 what less degree than during a naked fallow. But the additional vege- 

 table matter and manure which the gteen crops introduce into the soil, 

 and the large supplies of inorganic matter which such of them as are 

 deep-rooted bring up from beneath, amply compensate for any diminu- 

 tion they may cause in the benefits which are usually derived from the 

 naked fallow. 



§7. Of wheat u,ad wheaten flour. 



The grain of wheat in the hands of the miller is readily separated into 

 two portions — the husk, which forms the bran, and the greater portion 

 of the pollard — and the kernel, which, when ground, forms the wheaten 

 flour. The relative weights of these two parts vary very much. Some 

 varieties of grain are much smoother, more transparent, and thinner 

 skinned than others, and yield in consequence a larger return of the 

 finest flour. In good wheat the husk amounts to 14 or 13 percent, of 

 the whole weight* — though the quantity sei)arated by the miller is 

 sometimes not more than ^th (or 11 per cent.) of the weight of the 

 wheat. In making the fine white flour of the metropolis and other 

 large towns, about ^th of the whole is separated in the form of pollard 

 and bran. The proportion of the husk that can be sifted out at the mil?. 



* Boussingault found as much as 38,'^ per cent, of husk on a whiter wheat grown in the 

 botanic garden of Paris. Three lots of good Englisli wheat, ground at Mr. Robson's mill in 

 .Jurham, gave per cent. respectively- 

 Fine flour 74-2 751 77 9 



Boxings 9 83 CI 



Sharps 5 8 6-6 5-6 



• Bran 78 70 69 



Waste 32 30 35 



100 100 100 



