GROWTH AND WORK OF PLANTS 



resembles a little shield (fig. 17). The stem; the leaf bud, or 

 plumule, the root or radicle, the root sheath, and the scutellum 

 or cotyledon, make the young embryo in the corn seed. There 

 is still a large bulk of the content of the 

 grain which lies against the scutellum. 

 This is known as the endosperm. In 

 the corn it is largely made up of starch 

 which is stored food for the young 

 embryo when the seed germinates. 



18. Germination of the corn. 

 The root sheath usually emerges first 

 with the radicle of the embryo still 

 enclosed. While the root sheath is still 

 short, lengthwise sections will show that it has ceased to 

 elongate, and the root has pushed through it at one end. 



At this stage sections also show, when made through the middle 

 line of the embryo, the origin of the first two lateral roots. One 



cot 



Fig. 18. 



Corn grains sprouting; st. 

 starch; cot. cotyledon; pi. 

 plumule; r. radicle in root 

 sheath, the sheath still cover- 

 ing the root. 



Fig. 19. 



Germination of corn grains, showing origin of 

 first lateral roots. Note the radicle (primary 

 root) emerging from the root sheath. In right- 

 hand seedling, note the remains of root sheath 

 from which the radicle emerged. 



of them lies inside in the axis of 



the scutellum and the leaf, while 



the other lies opposite underneath 



the coat of the groove (see fig. 



19). They are really adventitious roots since they arise from 



the stem. The true lateral roots arise from the primary root 



Fig. 20. 



Germinating corn grains. Plumule and 

 primary root have emerged. 



