4 BULLETIN" 183, U. S. DEPARTMENT OF AGRICULTURE. 
THE SEED PROPER. 
The external layer of the seed proper is the aleurone layer. It 
assumes a greater importance in barlej^ than in other grains. It 
normally consists of a stratum of two or three rows of cubical cells 
gorged with protein contents. Their appearance shows them to be 
cells of unusual vigor and vitality. The greater part of the space 
within the aleurone layer is occupied b} r the starch endosperm. This 
is. as in all grasses, a typical storage tissue. Its cells are thin walled 
and packed with starch granules. The 
nuclei are feeble and distorted by the pres- 
sure of the accumulated starch. At the 
proximal end of the starch endosperm and 
partly embedded in its tissue lies the embryo, 
the morphology of which is observed with 
ease but interpreted with difficulty. From 
its nature, it must contain all the growing 
elements of the plant to be, as well as a num- 
ber of modified organs. The embryo lies 
obliquely to the long axis of the grain, its 
growing point directed toward the distal end. 
The true vegetative point is inclosed within 
the first leaves of the plant. In barley these 
are twisted, giving rise to the term a acro- 
spire" in place of "plumule." The plumule 
sheath surrounds all the upper vegetative 
portions. At the proximal end of the em- 
bryo is found a single main radicle. A short 
distance above, possibly at the first rudimen- 
tary internode, are five to eight secondary 
rootlets. When eight are present three are 
placed on either side and two toward the 
front. The space between the secondary 
rootlets and the growing point serves as 
a base for the attachment of the extra- 
embryonic tissue, the scutellum, or shield (fig. 2), which includes prac- 
tically all the remaining tissue. The origin and significance of this 
body as well as of the epiblast (absent in this genus, but common in 
grasses) has been variously interpreted. The scutellum is, however, 
generally conceded to be an absorbing organ. It is made up of thin- 
walled cells with large nuclei. Its inner surface rests directly upon 
the mass of the endosperm, and this surface of contact consists of a 
layer of elongated cells placed endwise to both the endosperm and 
the rest of the scutellar body. This layer, which is known as the 
epithelial layer, plays, according to the observations of the writers, 
a large part in the chemical activities of germination. 
Fig. 2.— A high-grade barley grain 
with the glumes removed to show 
the embryo with its coilarlike 
scutellum (s). The inner enve- 
lopes have been removed irom 
the upper part of the grain. 
