LIFE HISTORY OF THE MALE FERN 73 
gametophyte or sexual generation, beginning with the spore and 
ending with the fertilization of the egg to form the zygote or 
odspore. ‘The sporophyte gives rise to the gametophyte which in 
turn gives origin to the sporophyte. This is called “‘alternation of 
generations.” 
During this alternation of generations, a series of nuclear 
changes takes place in which the diploid chromosomes or full 
quota of the sporophyte generation are reduced to the haploid 
number in the gametophyte generation. These changes occur 
in the mitotic divisions of the spore mother cells to form spores 
which contain only half the number of chromosomes found in 
the spore mother cell and the rest of the sporophyte generation. 
At the time of fertilization the two gametes, antherozoid and 
ovum, fuse and restore the full quota or diploid number of 
chromosomes to the zygote. 
