SPOROPHYTES AND GAMETOPIIYTES in 



two metres in length. When we come to deal witli land 

 vegetation, this alternation of generations in some more or 

 less modified form is the absolute rule of all the higher forms. 



A braeken-fern affords a typical ex- 

 ample in which such an alternation of 

 generations can be easily and readily 

 recognized. If the back of a leaf of a fern 

 is examined, there will be found certain P^ 

 brownish powdery patches or stripes. 

 These are composed of receptacles — spor- 

 angia — which contain spores. The spores 

 are quite asexual, and when under certain 

 conditions the receptacle becomes rup- ''^^/j^^'l"[ 

 tured, these minute cells are easily blown tt^'/^ ''^' 

 about and scattered throughout the neioh- ^K> 

 bourhood. Since the fern, as one sees it, 

 bears spores, it is called a Sporoplujte, If ^^m. Young plant of 

 the history of the spore is followed, it will Maidenhair Fern still at- 

 be found that it comes to rest in very tachedtopiothallus(p); 



damp soil and gradually develops into a Iiter°Sachs?' ^''^ ^''''^' 

 little pad or heart-shaped green plant 

 known as the j^rothallus. The prothallus produces ova and 

 antherozoids. Since the cells which fuse are called gametes, 

 the prothallus which bears them is called a Gamdophijte. 



I A II B 



Fig. 61. Sexual^'organs of a Fern {Pohj podium vulgare). I. Rii)e female organ 

 in section; p, prothallus; o, egg or ovum. 11.^, the male organ wliicli produces 

 antherozoids. B, single antherozoid with its cilia for swimming, much 

 enlarged. 



The antherozoids require water to swim in so that tliev 

 may reach and penetrate the ovum. Hence the protlialhis 

 must live in a situation where at least from time to time it 

 has a watery coating. 



