48 HOW CROPS GROW. 



Starch (CeHioOj)!! is of very general occurrence in 

 plants. The cells of the seeds of wheat, corn, and all 

 other grains, and the tubers of the potato, contain this 

 familiar body in great abundance. It occurs also in the 

 wood of all forest trees, especially in autumn and winter. 

 It accumulates in extraordinary quantity in the pith of 

 some plants, as in the Sago-palm {Sdffus RumpMi), of 

 the Malay Islands, a single tree of which may yield 800 

 pounds. The onion, and various plants of the lily tribe, 

 are said to be entirely destitute of starch. 



The preparation of starch from the potato is very sim- 

 ple. The potato tuber contains about 70 per cent, water, 

 34 per cent starch, and 1 per cent of cellulose, while the 

 remaining 5 per cent consist mostly of matters which 

 are easily soluble in water. By grating, the potatoes are 

 reduced to a pulp ; the cells are thus broken and the 

 starch-grains set at liberty. The pulp is agitated on a 

 fine sieve, in a stream of water. The washings run off 

 milky from suspended starch, while the cell-tissue is re- 

 tained by the sieve. The milky liquid is allowed to rest 

 in vats until the starch is deposited. The water is then 

 poured off, and the starch is collected and dried. 



Wheat-starch may be obtained by allowing. wheaten 

 flour mixed with water to ferment for several' weeks. In 

 this process the gluten, etc., are converted into soluble 

 matters, which are removed by washing, from the unal- 

 tered starch. 



Starch is-now most largely manufactured from maize. 

 A dilute solution of caustic soda is used to dissolve the , 

 albuminoids (see p. 87). The starch and bran remaining 

 are separated by diffusing both in water, when the bran 

 rapidly settles, and the water, being run ofE at the proper 

 time, deposits nearly pure starch, the corn-starch of com- 

 merce. 



Starch is prepared by similar methods from rice, horse- 

 chestnuts, and various other plants. 



