STARCH AND PROTEIDS 275 



463. To test for starch: Make pastes with wheat flour, 

 potato starch, and corn starch. Treat a little of each with 

 a solution of rather dilute iodin. Try grains from crushed 

 rice with the same solution. Are they the same color? Cut 

 a thin section from a potato, treat with iodin and examine 

 under the microscope. To study starch grains: Mount in 

 cold water a few grains of starch from each of the following: 

 potato, wheat, arrow-root (buy at drug store), rice, oats, 

 corn, euphorbia. Study the sizes, forms, layers, fissures, 

 and location of nuclei, and make a drawing of a few grains 

 of each. 



464. Amylo-dextrine is a solid product of the cell much 

 resembling starch in structure, appearance, and use. With 

 the iodin-test the grains change to a wine-red color. Seeds 

 of rice, sorghum, wild rice, and other plants contain amylo- 

 dextrine. Amylo-dextrine is a half-way stage in the con- 

 version of starch into maltose and dextrine. These latter 

 substances do not react with iodin. 



465. Rroteid or nitrogenous matter is stored largely in 

 the form of aleurone grains, and is most abundant in seeds 

 of various kinds. It is present also in solution or in amorphous 

 compounds. The grains are very small, colorless or yellow- 

 ish in most plants, rarely red or green. In the common 

 cereals they occupy the outer layer of cells of the endosperm. 

 (Fig. 445.) In many other cases they are distributed through- 

 out the seed. The grains vary in size and 



form in different species, but are rather 

 constant within each group. They are en- 

 tirely soluble in water unless certain hard 

 parts or bodies, known as inclusions, are 



, . , . TIT m>' Aleurone grains 



present, and these may remain undissolved. (ai) in kernel of 

 The inclusions may be (a) crystaloids, as wheat - 

 in potato, castor-oil seed; (6) globoids, as in peach, mustard; 

 (c) calcium oxalate crystals, as in grape seed. 



466. To study alevrone grains and their inclusions: Cut 



