l82 STRUCTURE AND LIFE HISTORIES 



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. 



166. Alternation of Generations. Our study of the 

 fern also brought out another fact of very fundamental 

 importance. Sporophytes do not produce sporophytes, 

 nor gametophytes, gametophytes; 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) 



Antheridium Archegonium 



4 4 



Sperm (male gamete) Egg (female gamete) 



Fertilization 



Oosperm (zygote) 

 Embryo 



4-4- . 



Mature sporophyte (mature zygote) 



U 



Sporophyll 



orop 



Sporangium 

 Spore-mother-cell 



Mil 



Spore Spore Spore Spore 

 Gametophyte 



Reduction 



