182 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 — >o6sperm — >sporophyte. 



The order of structures and processes involved in the 

 life-cycle is as follows: 



OUTLINE OF LIFE HISTORY OF A FERN 



Gametophyte (prothallus) 

 I 



T T 



Antheridium Archegonium 



I I 



Sperm (male gamete) Egg (female gamete) 



Fertilisallon 



Oosperm (zygote) 



Embryo 



Mature sporophyte (mature zygote) 



Sporophyll 



Sporangium 



S pore-mother-cell 



T 



Reduction 



Spore Spore Spore Spore 



i 



Gametophyte 



