100 



RESULTS WITH POTATOES 



in the experimental potatoes, but the specific gravity of the 

 potatoes, and the percentage of dry matter which they contain, 

 both of which characters follow the proportion of starch, have 

 been regularly determined. The following table shows the 

 results of the determinations just referred to, and also the per- 

 centage of ash, and nitrogen, found in the dry matter. 



TABLE XXXIII. 



COMPOSITION OF POTATOES GROWN WITH VARIOUS MANURES 

 AT ROTHAMSTED, AVERAGE OF TWELVE YEARS, 1876 87. 



It will be observed that the specific gravity, and the per- 

 centage of dry matter rise and fall together. In each case the 

 unmanured tuber is the one which stands highest in the scale 

 in these respects. With each addition to the bulk of the crop 

 the composition of the tuber becomes somewhat more watery. 



The proportion of ash is naturally highest where only ash 

 constituents have been supplied, and lowest where ammonia 

 salts have been used without any supply of cinereals. 



The proportion of nitrogenous matter naturally follows an 

 inverse order to the ash, being highest where ammonia salts 

 are used alone, and lowest with the purely cinereal manure. 

 In the case of plots 3 and 7, receiving a well-balanced manure, 

 supplying both nitrogen and ash constituents, there is neither 

 an excess or deficiency of nitrogenous matter in the tuber. 



