290 



GENERAL BOTANY 



liberated male gametes become entangled. The male . gametes 

 then swim down the canal of the neck, made by the disorgani- 

 zation of the canal cells, and one successful gamete enters the 

 egg and fertilizes it. The unsuccessful gametes, as in the algge 

 and fungi, are unable to penetrate the fertilized egg cell and die 

 in the neck canal or the venter. 



Sporophyte. The zygote germinates at once without passing 

 through a resting period as in the algse. The growth of the 

 zygote (Fig. 160) is accompanied by cell division and differen- 

 tiation as in the zygote of the mandrake or the bean. The embryo 



\ 



Venter cell 



Wall cells 



Spore 

 mother eel 



FIG. 160. Development of spores (sporogenesis) in Eicciocarpus 



a, early spore mother-cell stage, with mother cells forming a cellular tissue ; 6, the 



mother cells, after becoming free, have each divided twice and formed four cells, 



called a tetrad ; c, the four cells of each tetrad in 6 separating to form four spores 



which results is, however, very simple in Ricciocarpus as com- 

 pared with the embryos of the higher plants just referred to. It 

 is composed of an outer layer of wall cells which incloses and 

 protects a mass of cells which ultimately become the mother 

 cells of spores. With the enlargement of the embryo the spore 

 mother cells become free from each other, and each mother cell 

 divides twice to form groups of cells in fours, called tetrads. 

 Each cell of a tetrad gives rise to a spore. By this process the 

 embryo is converted into a spore case, or sporangium, filled with 

 spores. The rupture of the wall of this spore case -liberates the 

 spores, which then germinate at once to form new plants in a 

 proper habitat. 



Such a plant body as that described above, which results 

 from cell division and differentiation of the zygote, is called a 

 sporophyte, since its main function is the bearing of spores. 



