56 HYDROCARBONACEOUS PROXIMATE PRINCIPLES. 



QUANTITY OF STARCH IN 100 PARTS IN 



Wheat . 

 Rye 



Oats . 

 Barley . 

 Indian corn 

 Rice 



57.88 

 64.65 

 60.59 

 66.43 

 67.55 

 88.65 



Potatoes 

 Sweet potatoes 

 Peas 

 Beans . 

 Flaxseed 

 Chocolate nut 



20.00 

 16.05 

 37.30 

 33.00 

 23.40 

 11.00 



When purified from foreign substances starch is a white, glistening 

 powder, which gives rise to a peculiar crackling sensation if rubbed 

 between the fingers. It consists of minute granules of very firm con- 

 sistency and definite shape, presenting certain peculiarities, of both form 

 and size, by which its varieties, derived from different sources, may be 

 distinguished from each other. The young starch granules, when first 

 produced in the tissues of the plant, are exceedingly small, round, and 

 perfectly homogeneous ; but they afterward increase in size, and, as their 

 growth is irregular, they become ovoid, pear-shaped, lenticular, or 

 polygonal in form. They also show under the microscope a definite 

 structure, each granule being composed of a series of layers, disposed 

 one over the other, giving rise to the appearance of concentric markings, 

 which are very characteristic of most varieties of starch grains, after 

 they have attained a certain size. The markings are arranged round a 

 single point, usually more or less eccentric in position, which is called 

 the hilum. 



The successive layers of which the starch granule is composed differ 

 from each other mainly in their consistency, being alternately harder 



and softer in comparison with 

 each other; and this difference 

 in density produces a corres- 

 ponding difference in the refrac- 

 tive power of the layers, and 

 consequently an appearance of 

 concentric striation. 



Each starch granule, further- 

 more, consists of two sub- 

 stances, intimately mingled in 

 every part of its mass, which re- 

 semble each other completely in 

 chemicalcomposition, but differ 

 greatly in solubility. These 

 two substances are, 1st, granu- 

 lose, which may be extracted 



GRAINS OP POTATO STABCH. f m the starch S ^ b U - 



ing water ; and 2d, cellulose, 



which remains undissolved. The granulose is usually much the more 

 abundant of the two, but the cellulose has so marked a consistency that 

 it retains the form and apparent laminated structure of the starch grain. 



