CELL CONTENTS 



197 



Deposits of tannin are colored bluish black with a solution 

 of ferric chloride. 



ALEURONE GRAINS 



Aleurone grains are small granules of variable structure, 

 size, and form, and they are composed of reserve proteins. 

 They occur in celery, fennel, coriander, and anise, fruits, in 

 sesame, sunflower, curcas, castor oil, croton oil, bitter almond, 

 and other oil seeds. 



In many of the seeds the aleurone grains completely fill the 

 cells of the endosperm, embryo, and peristerm. In wheat, rye, 

 barley, oats, and corn the aleurone grains occur only in the 

 outer layer or layers of the endosperm, the remaining layers 

 in these cases being filled with starch. 



In powdered drugs the aleurone grains occur in parenchyma 

 cells or free in the field. 



STRUCTURE OF ALEURONE GRAINS 



Aleurone grains are very variable in structure. The simplest 

 grains consist of an undifferentiated mass of proteid substance 

 surrounded by a thin outer membrane. In other grains the 

 proteid substance encloses one or more rounded denser proteid 

 bodies known as globoids. In other grains a crystalloid— crystal- 

 like proteid substance — is present in addition to the globoid. 

 In some grains are crystals of calcium oxalate, which may occur 

 as prisms or as rosettes. All the different parts, however, do 

 not occur in any one grain. In castor-oil seed (Plate 77a, Fig. 8) 

 are shown the membrane (^4), the ground mass (B), the crys- 

 talloid (C), and the globoid (D). 



FORM OF ALEURONE GRAINS 



Much attention has been given to the study of the special 

 parts of the aleurone grains, but one of the most important 

 diagnostic characters has been overlooked, namely, that of 

 comparative form. For the purposes of comparing the forms of 

 different grains, they should be mounted in a medium in which 

 the grain and its various parts are insoluble. Oil of cedar is 

 such a medium. The variation in form and size of the aleurone 

 grains when mounted in oil of cedar is shown in Plate 77a. 



