22 PLANT BIOLOGY 



This is formed by a union of the funiculus, or seed-stalk, 

 with the seed-coats, and through it food was transferred 

 for the development of the seed, but it is now functionless. 



Seeds differ wonderfully in size, shape, color, and other 

 characteristics. They also vary in longevity. These 

 characteristics are peculiar to the species or kind. Some 

 seeds maintain life only a few weeks or even days, whereas 

 others will " keep " for ten or twenty years. In special 

 cases, seeds have retained vitality longer than this limit, 

 but the stories that live seeds, several thousand years old, 

 have been taken from the wrappings of mummies are un- 

 founded. 



Germination. The embryo is not dead ; it is only dor- 

 mant. When supplied with moisture, warmth, and oxygen 

 (air), it awakes and grows : this growth is germination. 

 The embryo lives for a time on the stored food, but gradu- 

 ally the plantlet secures a foothold in the soil and gathers 

 food for itself. When the plantlet is finally able to shift 

 for itself, germination is complete. 



Early Stages of Seedling. The germinating seed first 

 absorbs water, and swells. The starchy matters gradually 

 become soluble. The seed-coats are ruptured, the caulicle 

 and plumule emerge. During this process the seed 

 respires freely, throwing off carbon dioxid (CO 2 ). 



The caulicle usually elongates, and from its lower end 

 roots are emitted. The elongating caulicle is known as 

 the hypocotyl ("below the cotyledons"). That is, the 

 hypocotyl is that part of the stem of the plantlet lying 

 between the roots and the cotyledon. The general direc- 

 tion of the young hypocotyl, or emerging caulicle, is down- 

 wards. As soon as roots form, it becomes fixed and its 

 subsequent growth tends to raise the cotyledons above the 

 ground, as in the bean. When cotyledons rise into the 



