STARCH, 



STARCH is the most generally diffused, excepting protoplasm, 

 of all vegetable substances within the cell-wall. When found 

 in the older structures, roots, stems, seeds, etc., it is found nearly 

 pure; when found in freshly-growing tissue it <s in union with chlo- 

 rophyll. Starch grains contain carbon, oxygen, hydrogen, and some 

 mineral matter. They are insoluble in water, alcohol, ether, and oil; 

 are destroyed by potassa, and colored blue or violet by iodine the 

 color depending on the density of the granule and the strength of 

 the iodine. The starch grains of different families and different 

 species of the same family differ so much in size and general appear- 

 ance as to be easily identified. The largest starch grains known are 

 those of tous-les-mois, which are frequently ^-J-^ of an inch in length, 

 while the smallest are those of rice, which are occasionally -g ^ of 

 an inch in diameter. 



Potato Starch. Botanists have taken the potato-starch grain as the 

 typical form with which they compare others. If the commercial starch 

 is not accessible, the grains can easily be obtained by cutting a fresh 

 potato with a clean knife, and then floating on a glass slide, with a 

 drop of water, the white substance which adheres to the side of the 

 knife. Or, shave off a very thin slice of the potato, and place it in 

 a watch-crystal in a little water ; the fine sediment settling to the 

 bottom will be the starch. There are two leading theories regarding 

 their growth. Some claim that the surface of the grain is formed 

 first, and that it grows by layers being deposited on the inner surface 

 of the case, which gradually expands until it reaches its normal size. 

 The other and the more generally accepted opinion is, that the 

 nucleus is formed first, and the grain grows by means of deposits of 

 starchy matter around this nucleus, and each successive layer con- 

 tains less moisture than the preceding layer ; this explains the ap- 

 pearance of rings or laminae seen so plainly in the potato and many 

 other starches. A new theory has been advanced in Sach's Botany 



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