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 



i i 



Sperm (male gamete) Egg (female gamete) 



Fertilization 



Oosperm (zygote) 



4.4. 



Embryo 



ii 



Mature sporophyte (mature zygote) 



4.4. 



Sporophyll 



ii 



Sporangium 



4.4. 



Spore-mother-cell 



Ar Ar Ar Ar 



Spore Spore Spore Spore 



i 



Gametophyte 



Reduction 



