FLOWERLESS PLANTS 



155 



A, the archegonium with egg (e) and canal (c); 

 B, antheridium; C, antherozoid, very 

 highly magnified, — Strasburger. 



forming the neck of the flask. FertiHzation is essentially the 

 same process that has been described for the flowering plants, the 

 sperm cell uniting with the 

 egg cell to form a single cell, 

 the fertilized egg. 



Sporophyte and Gameto- 

 phyte. — The direct result of 

 fertilization is the growth of 

 the egg cell by repeated divi- 

 sion to form a little fern plant. 

 Later the young plant strikes 

 root, the prothallus dies away, 

 and we have a fern plant which 

 will later in the season pro- 

 duce asexual spores. The 

 leafy fern plant, because it produces asexual spores, is called the 

 sporophyte. The prothallus, which forms the eggs and sperms, 

 both of which are known as gametes, or sex cells, is called the 

 gametophyte. 



Alternation of Generations. — The fern plant during its entire 

 life thus passes through two entirely different stages, or genera- 

 tions. The spore germinates to form a gametophyte, or sexual 

 generation. This sexual generation in turn produces an asexual 

 generation, or sporophyte. The alternation, in the life history of a 

 plant or animal, of a sexual stage with an asexual stage is called an 

 alternation of generations. 



General Characters of the Fernlike Plants. — These plants pass 

 through an alternation of generations ; they have a distinct root, 

 stem, and leaves; and the stem possesses conducting tubes or Jibro- 

 vascular bundles; these are the distinguishing marks of the ferns 

 and their allies. Fern plants show a great diversity in form 

 and size. They vary from the great tree ferns of the tropics, 

 some of which are thirty to forty feet in height, to tiny forms of 

 almost microscopic size. The leaves of the ferns are among the 

 most complex in form of any that we know. The position and 

 shape of the spore cases differ greatly in different species of ferns; 

 ,in some the edge of the leaflet is modified to hold the spores, in 



