THE POTATO 289 



tato may be classed, though not botanically re- 

 lated thereto, the sweet potato and the yam. 

 Among cereals rice has the largest percentage of 

 starch and oats the smallest. The potato, as 

 grown for the table, has an average content of 

 about 15 per cent, of starch. When a potato is 

 grown specifically for the production of alcohol it 

 contains a larger quantity, or nearly 20 per cent. 

 Cassava contains a larger percentage of starch 

 than the potato, varying from 20 to 30 per cent. 



"Under the microscope the granules of potato 

 starch have a distinctive appearance. They ap- 

 pear as egg-shaped bodies on which, especially the 

 larger ones, various ring-like lines are seen. With 

 a modified light under certain conditions of ob- 

 servation a black cross is developed upon the gran- 

 ule. It is not difficult for an expert microscopist 

 to distinguish potato from other forms of starch 

 by this appearance. 



"The mineral matters which the potato ex- 

 tracts from the soil or from the fertilizers which 

 are added thereto consist chiefly of phosphate and 

 potash. The mean average composition of the 

 ash of the potato is shown in the following table: 



Potash (K 2 O) 60.3 



Soda (NaoO) 2.62 



Lime (Cab) 2.57 



Magnesia (MgO) 4.69 



Iron oxid. (Fe 2 O 3 ) 1.18 



Phosphoric acid (P 2 O S ) 17.33 



Sulphuric acid (SO 3 ) 6.49 



Chlorin 3.11 



Silicic acid (SiO a ) 2.13 



"This analysis was made upon the so-called 

 pure ash, deprived of its unburned carbon, and 

 freed of sand and carbon dioxid. 



