216 



cent.,' and from these percentages the value of any 

 given yield per acre can be reckoned. 



" The difference between Imperator (27 '5 per cent.) 

 and Reading Giant (20*9 per cent.) to take two 

 typical, late, heavy-cropping varieties, one round and 

 one kidney is no less than 6*6 per cent. In other 

 words, the difference between two crops, each of 

 20 tons of tubers, showing these specific gravities 

 respectively, amounts to 26 cwt. of dry solid matter. 



" In 1892 the specific gravities of the ten varieties 

 grown ranged from 1*0935 to 1*0807, Imperators being 

 then also the highest, and all the round varieties 

 higher than the kidneys. The variations were in 

 1893 very much wider, and the higher specific gravities 

 are very much higher than any shown in 1892, but 

 the variation shown in ordinary years is well worth 

 taking account of, although it may not amount to 

 one-half of that shown in 1893. 



" If the values deduced from the observed specific 

 gravities are to be relied on, it is possible to go further 

 and compute the weight of digestible matter contained 

 in crops of different varieties. 



"Wolff's experiments in Germany are very generally 

 accepted as yielding correct nutritive values for 

 different feeding materials. In the experiment with 

 pigs it was found that they digested 98 per cent, of 

 the starch, or 94 per cent, of the total organic matter 

 of potatoes. It would appear, therefore, to be quite 

 safe to assume that 90 per cent, of the total dry con- 

 stituents of the tubers are digestible. As a matter of 



