FORM AND STRUCTURE 13 



layers being deposited concentrically around a point 

 called the hilum. Chemically, a starch grain is composed 

 of carbohydrates of which there are two forms ; (1) the 

 starch-cellulose or puter layer similar to ordinary cellu- 

 lose, and (2) an inner portion, termed granulose, which 

 readily dissolves with dilute sulphuric or hydrochloric 

 acid. It is this part which gives the characteristic 

 test for starch, the blue color in presence of iodine. The 



FIG. 6. Cross-section through the embryonic portion only of the wheat 

 kernel: a, first seminal root; b, second seminal root; c, third semi- 

 nal root; d, epithelial cells; e, testa. (X42.) 



starch grains of glutinous rices and proso millet (Panicum 

 miliaceum) turn red or reddish brown, instead of blue, 

 under the same test, probably because of some modifica- 

 tion in their composition. 



12. Aleurone grains. The reserve-proteins of the 

 seed are contained in the aleurone grains, which are 

 smaller and less developed in the starchy seeds of cereals 

 than in oily seeds. They are rather complex bodies, con- 

 taining a mineral portion composed usually of a double 



