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 (A), 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 
sucha medium. The variation in form and size of the aleurone 
grains when mounted in oil of cedar is shown in Plate 77a. 
