34 HEREDITY AND EVOLUTION IN PLANTS 



gametophyte, on the other hand, being derived from a sin- 

 gle reproductive cell (the spore), without nuclear or cell-fu- 

 sions, is composed of cells of a single or haploid nature. 



26. Alternation of Generations. Our study of the 

 fern also brought out another fact of very fundamental 

 importance. Sporophytes do not produce sporophytes, 

 nor gametophytes, gametophy tes ; but there is always 

 an alternation of generations, sporophytes producing 

 gametophytes, and gametophytes, sporophytes. 



The order of sequence in the life-cycle is as follows: 



sporophyte >spore ^gametophyte >gametes oosperm sporophyte. 



The order of structures and processes involved in the 

 life-cycle is as follows : 



OUTLINE OF LIFE HISTORY OF A FERN 



Gametophyte (prothallus) 



T; 4 



Antheridium Archegonium 



4 4 



Sperm (male gamete) Egg (female gamete) 



Fertilization 



Oosperm (zygote) 



44 



Embryo 



44 



Mature sporophyte (mature zygote) 



44 



Sporophyll 



44 



Sporangium 



44 



Spore-mother-cell 



[ 



eduction 



Spore Spore Spore Spore 



4 



Gametophyte 



