72 THE POTATO CROP. 



been given ; their organic composition lias been examined 

 by Boussingault, and given by him as under: 



Dr. Fromberg's analyses give a far lower estimate of the 

 nitrogen and of the mineral constituents of the "shaws;" 

 and as these have reference to potatoes grown in this 

 country, while Boussingault's refer to the produce of the 

 Continent, where the plant is less luxuriant and herbaceous 

 in its habit than with us, it will be safer to take Dr. From- 

 berg's results in our estimates of their manurial value. 



The results of these several analyses show us the probable 

 average amount of substances abstracted from the soil 

 during the growth of the crop, and the relative proportions 

 carried off the farm by the tubers, or returned to it again by 

 the stems or shaws. They also enable us to form a correct 

 estimate of the real value of the crop to us as a source of 

 food-supply, whether for ourselves or for our stock, and show 

 us that although the potato ranks far below any of our 

 usual bread-corns in its individual nutritive value, still, 

 owing to its superior produce per acre, the aggregate 

 amount of food produced is considerably in excess of that 

 obtained from either of those crops. Thus a crop of wheat 

 of 32 bushels to the acre, would contain of nitrogen com- 

 pounds (at 12 per cent.), about 240 Ibs., and of starch (at 

 55 per cent.), about 1350 Ibs. ; while a crop of potatoes, of 

 8 tons per acre, would contain of nitrogen compounds (cal- 

 culated at 2 per cent.) about 358 Ibs., and of starch, at an 

 average of 15 per cent., about 2685 Ibs. 



