8 BULLETIN 183, U. S. DEPARTMEXT OF AGRICULTURE. 



Within the embryo various tissues arise. A primary radicle and 



from five to eight secondary rootlets, inclosed in their sheathing 



tissues, are directed toward the proximal end of the grain. The 



plumule \vithin the plumule sheath points up over the endosperm 



toward the distal end of the seed. Attached midway between the 



root and plumule— that is, to the hypocotyl — by a wide ligament, or 



umbilicus, is the scutellum. This organ spreads out over the 



entire surface of the endosperm lying next to the embryo and has 



on its inner or adjacent surface a layer of specialized cells — the 



epithelial layer. 



GERMINATION. 



Germination is the continuation of the growth of the embryo, 

 arrested at the time of the maturation of the seed. The first step in 

 germination is a distension of the grain, due to the absorption of 

 water. In the resting stage most of the tissues of the embryo are 

 free from starch. When first brought under conditions favorable 

 for germination the few starch grains present disappear. Very 

 shortly, however, starch again becomes evident in tissues that were 

 perfectly free from it at maturity. In the outer layers of the scutel- 

 lum a marked deposit is soon apparent. As the process advances, 

 the cells of the epithelial layer elongate shghtly. Brown and Mor- 

 ris ^ noticed that one of the first changes in the grain was in the 

 appearance of the protoplasm of these cells. In the resting state 

 this is clear and finely granular. As the first steps of germination 

 are in progress it assumes a much coarser character and the cell 

 becomes cloudy. This condition obtains until the endosperm is 

 almost entirely absorbed. 



The first actual formation of new tissue takes place in the primary 

 radicle. This breaks through the coleorhiza and is the first part of 

 the plant to emerge from the grain. The secondary rootlets are 

 shghtly less advanced. The plumule develops more slowly, and 

 under restrained malting conditions it may be several days in reach- 

 ing less than the length of the grain. 



In the endosperm, germination is, of course, a process of destruc- 

 tion. In the history of a single cell the walls first become thickened 

 as if distended with water. The laminae become distinct, the waUs 

 become translucent, and disintegration sets in. Various investi- 

 gators have asserted that a complete obhteration of the walls takes 

 place, but the ^^Titers have not been able to arrive at this conclusion, 

 the walls always being discoverable to some extent, especially by 

 means of staining. As soon as they have been sufficiently weakened, 

 action begins upon the starch grains. Their dissolution in this case 

 is not by the translocation process, in which they gradually become 



1 Brown, H. T., and Morris, G. H. Researches on the germination of some of the GramJneae, part 1, 

 Journal, Chemical Society [London], v. 57 (Transactions), p. 458-528, 1890. 



