64 HOW CROPS GROW. 



granules, c. In maize and rice the grains are usually so 

 densely packed in the cells as to present an angular (six- 

 sided) outline, as in d. The starch of the bean and pea 

 has the appearance of e. The minute starch-grains of the 

 parsnip are represented at/", and those of the beet at g. 



The grains of potato-starch are among the largest, be- 

 ing often l-300th of an inch in diameter ; wheat-starch 

 grains are about l-1000th of an inch ; those of rice, l-3000th 

 of an inch, while those of the beet-root are still smaller. 



Unorganized Starch exists as a jelly in several plants, according to 

 Sclileiden, (Botanlk p. 127). Dragendorff asserts, that in the seeds of 

 colza and mustard the starch does not occur in the form of grains, but 

 in an unorganized state, which he considers to be the same as that no- 

 ticed by Schleiden. 



The starch-grains are unacted upon by cold water, un- 

 less broken, (see Exp. 26,) and quickly settle from suspen- 

 sion in it. 



When starch is triturated for a long time with cold water, whereby the 

 grains are broken, the liquid, after filtering or standing until perfectly 

 clear, contains starch in extremely minute quantity. 



When starch is heated to near boiling with 12 to 15 times its weight 

 of water, the grains swell and burst, or exfoliate, the water is absorbed, 

 and the whole forms a jelly. This is the starch-paste used by the laun- 

 dress for stiffening muslin. The starch is but very slightly dissolved ~by 

 this treatment ; see Exp. 27. On freezing, it separates almost perfectly. 



When starch-paste is dried, it forms a hard, horn-like mass. 



Tapioca and Sago are starch, which, from being heated while still 

 moist, is partially converted into starch-paste, and, on drying, acquires a 

 more or less translucent aspect. Tapioca is obtained from the roots of 

 the Manihot, a plant which is cultivated in the West Indies and South 

 America. Cassava is a preparation of the same starch, roasted. Sago is 

 made in the islands of the East Indian Archipelago, from the pith of 

 palms. It is granulated by forcing the paste through metallic sieves. 

 Both tapioca and sago are now imitated from, potato starch. 



Test for Starch. The chemist is enabled to recognize 

 starch with the greatest ease and certainty by its peculiar 

 deportment towards iodine, which, when dissolved in wa- 

 ter or alcohol and brought in contact with starch, gives 

 it a beautiful purple or blue color. This test may be used 

 even in microscopic observations with the utmost facility. 



