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 barley 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 vitahty. The greater part of the space 

 within the aleurone layer is occupied by the starch endosperm. This 

 is, as in aU grasses, a typical storage tissue. Its cells arc thin walled 



;ind 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 '^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 scuteUum 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 

 epithehal 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 collarlike 

 scutellum (s). The inner enve- 

 lopes have been removed from 

 the upper part ot the grain. 



