1 10 Bitrnsiite. 



ducing another fern-plant, each spore gives rise to a little 

 heart-shaped, leaf-like structure, called a prothallium. On 

 this grow two distinct kinds of minute bodies, one of which 

 contains a germ cell with a canal leading to it, the other 

 gives off, when mature, little ciliated cells, some of which 

 make their way through the canal into the germ cell, and 



FIG. 20. PART OF MATURE FKOND OF BRACKEN (Pteris aquilina). 

 Underside showing Sporangia. 



fertilise it. From the fertilised germ-cell a true fern is 

 developed. Thus we get fern, prothallium fern, prothallium, 

 etc. It will be seen that only the alternate generations 

 resemble each other, and from this circumstance the process 

 has been designated the " alternation of generations " ; this 

 was once pithily defined by an eminent naturalist as a pro- 

 cess in which each individual is exactly like its grand- 

 mother, but bears no resemblance to its mother. 



We have called the leaf-like parts of the fern fronds, and 

 very beautiful some of them are, but they must not be con- 

 founded with leaves ; they are really leaves and flowers 



