STARCH PROTEIN 249 



Starch turns blue with iodine (75). The color may be 

 driven away by heat, but will return again as the tempera- 

 ture lowers. 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 iodine. Try grains from 

 crushed rice with the same solution. Are they the same 

 color? Cut a thin section from a potato, treat with iodine 

 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. 



402. Amylo-dextrine is a solid product of the cell 

 much resembling starch in structure, appearance, and use. 

 With the iodine -test the grains change to a wine -red color. 

 Seeds of rice, sorghum, wild rice, and other plants contain 

 am ylo- dextrine. Amylo-dextrine is a half-way stage in 

 the conversion of starch into maltose and dextrine. These 

 latter substances do not react with iodine. 



403. Protein or nitrogenous matter occurs largely in 

 the form of aleurone grains, and is most abundant in 

 seeds of various kinds. The grains are very small, color- 

 less or yellowish in most plants, rarely red or green. In 

 the common cereals they occupy the outer ^^^^ ^ 

 layer of cells of the endosperm. Fig. 392. 



In many other cases they are distributed 

 throughout the seed. The grains vary in 

 size and form in different species, but 



.-, . ., . , 392. Aleurone grains 



are rather constant within each group. ( a i) m kernel of 

 They are entirely soluble in water unless wheat - 

 certain hard parts or bodies, known as inclusions, are 

 present, and these may remain undissolved. The in- 

 clusions may be (a) crystaloids, as in potato, castor- oil 

 seed; (&) globoids, as in peach, mustard ; (c) calcium oxa- 



