70 THE POTATO CEOP. 



The proportion of starch appears to increase in the grow- 

 ing plant until it reaches its maturity, after which, on 

 being removed from the ground, it appears to decrease in 

 the same regular proportion. Dr. Fromberg, on examin- 

 ing tubers of the same variety, found that the starch 

 had increased from 1673 to 21 per cent, in the two months 

 immediately preceding its maturity; and Pay en found 

 that the same variety of potato contained in 



October, 17'2 per cent, of starch. 



November, 16'8 



December, 15'6 



January, 15*5 



February, 15'2 



March, 15'0 



April, 14-5 



Thus we see the proportion of starch varies with the 

 age of the plant, and also with the period that it is kept 

 after the maturity of the tubers ; besides these, the soil 

 and climate also exert influence upon it. In an experiment 

 with the same varieties grown in different localities, it 

 was found that 



Buffs grown in Forfarshire gave 20*71 per cent. 



Mid-Lothian ,, 14'89 



Cups grown in Argyleshire gave 15' 14 ,, 



Mid-Lothian 18'94 and 23'82 per cent. 



Since the prevalence of the potato disease in this coun- 

 try, and, indeed/ on the Continent, the attention of scien- 

 tific and of practical men has been attracted to the best 

 means of utilizing those tubers which are injured by the 

 disease, and have become unfit for use as articles of food. 

 In this country, the separation of their starch is the simple 

 and only way of utilizing them. On the Continent, they 

 continue the manufacturing process by converting the 

 starch firstly into sugar, and subsequently into spirits. The 

 first is only a mechanical process of separation ; the potatoes 

 are rasped down into a fine pulp, and the starch granules 

 washed through sieves, the coarser portions of the cellular 



