12 



GROWTH AND WORK OF PLANTS 



Fig. 14. 



Germinating seed of pumpkin, showin^ how the heel or 

 'peg' 1 



embryo within. Between the embryo and the seed coats is a 



thin papery lining, the dead and dry remnant of the endosperm. 



The radicle of the embryo is short, conic, and lies at the micro- 



pylar end. The stem 

 is extremely short, but 

 the two cotyledons are 

 large and fleshy, form- 

 ing the bulk of the em- 

 bryo. They are easily 



hes-on the seed coat to cast it "off. separable and the tiny 



plumule lies between 



them at the stem end of the embryo. In the squash and pumpkin, 



as in the bean and pea, the endosperm was all consumed during 



the formation of the seed and stored in the cotyledons. 

 15. Germination of the squash 



or pumpkin seed. The root emerges 



from the hilum end of the seed coats, 



and soon turns downward. On the 



underside of the stem, as the seed lies 



horizontally, and directly within the 



" jaws" of the split seed coats, a small 



and stout protuberance is formed 



which is called the "peg" (fig. 14). 



This holds the lower half of the seed 



coat firmly down while the arching of 



the hypocotyl and cotyledons pries the seed coats farther apart 



and allows the cotyledons to be drawn out of the seed coats. 



Otherwise the seed coats, which do not split entirely apart, 



would pinch so tightly on the cotyledons that it would be very 



difficult for them to escape. 



Fig. 15- 



Pumpkin seedling rising from the 

 ound. 



groun 



CORN SEEDLINGS. 



16. Form of the grain of corn. The form and color of the 

 grains of corn vary in different varieties. They are usually flat- 

 tened, somewhat wedge-shaped in outline, smooth and rounded 



