34 III;KKDITY 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, 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 K)6sperm 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) 



Fertilisation 



^* ^ 



Oosperm (zygote) 



44 



Embryo 



44 



Mature sporophyte (mature zygote) 



44 



Sporophyll 



44" 



Sporangium 



44 



Spore-mot her-ccl I 



4 ill \ Rfduciim 



Spoxe S{)ore Spore Spore 



4 



Gametophyte 



