134 



COLLEGE BOTANY 



of enzymes and transported to other parts of the plant for imme- 

 diate use as food or for storage for future use. The form and 

 structure of the starch grains varies in different species of 

 plants and in different parts of the same plant. The most gen- 

 erally accepted formula of starch is (C 6 H 10 O 5 ) n , but it has been 

 shown that it is in reality made up of two substances. Starch 



grains a-re ovoidal or 

 spherical or poly- 

 gonal and show a more 

 or less distinct point 

 or origin of growth 

 known as the hilum. 

 The two substances 

 are laid down in more 

 or less distinct layers. 

 The starch grains are 

 usually single, but 

 may be formed in 

 groups of two or three 

 or four or in the case 

 of some of the cereals 



Section of potato showing (o and b) the epider- of 100 fiTS-inS. Starch 

 rs of cells; (c) the inner cells and starch grains. 



is slightly soluble in 



water and gives a. blue or blue-black color when treated with 

 iodine. It can. be transformed by heat, by enzymes, and by 

 dilute acids into dextrin (Figs. 91, 92, 93, 94). 



Starch is one of the most important of the plant products. 

 Although it is manufactured in the green parts of the plant, it 

 is stored in practically all parts of the plant. It is found in con- 

 siderable quantities in stems and roots, especially at the close 



FIG. 91. 

 mal laye 



