GYMNOSPERMS 



335 



in June (Fig. 198, a). Just before fertilization the end of the 

 pollen tube penetrates the neck of an archegonium and then 

 ruptures, liberating the male cells in contact with the egg. 

 The union of one of these male cells with the egg cell com- 

 pletes ttye process of fertilization and initiates the formation of 

 the embryo. 



Embryo. As soon as fertilization has taken place, the con- 

 jugate nucleus, formed by the union of the male and female 



i 



Cotyledons 



Hypocotyl 



a Mlcropyk Micropyle^ 



FIG; 199. The ovule, seed, and seedling of the spruce 



a, ovule at the time of fertilization'; b, two embryos developing as a result of fertili- 

 zation ; c, seed developed from a with only one'embryo ; d, young seedling developed 

 from a seed by germination and growth 



pronuclei, divides to form eight nuclei, which then pass to the 

 bottom of the egg. Around these nuclei eight cells are ulti- 

 mately formed, which constitute the beginning of the pro- 

 embryo. This proembryx) soon differentiates into a suspensor, 

 composed of four greatly elongated cells, and the embryonic 

 cells which are to form the embryo proper (Fig. 199, J). The 

 embryonic cells finally produce the embryo within the seed. 

 This embryo is composed of the 'hypocotyl, or stem, the root, 

 and numerous first leaves, or cotyledons, surrounding the ter- 

 minal plumule, or bud. These structures are shown more 

 plainly in Fig. 199, 6?, which represents a seedling sporophyte of 

 the spruce produced by the germination of the seed. The seed 



