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) 
4 ^4 
Antheridium Archegonium 
4 4 
Sperm (male gamete) Egg (female gamete) 
Fertilization 
^i ^ 
Oosperm (zygote) 
44 
Embryo 
44 
Mature sporophyte (mature zygote) 
44 
Sporophyll 
44 
Sporangium 
44 
Spore-mother-cell 
4" 4' 4" -vr 
Spore Spore Spore Spore 
4 
Gametophyte 
Reduction 
