CHAPTER IX. 



ALTERNATION OF GENERATION THE BRACKEN FERN 

 (PTERIS) STRUCTURE OF THE SPOROPHYTE OF PTERIS. 



Alternation of generation. 



The study of the fern is introduced in this place 

 because of the remarkable manner of reproduction 

 known as alternation of generation which this plant 

 presents. Alternation of generation is especially inter- 

 esting because it gives a key to the relationship of the 

 higher plants, such as the sunflower and the oak, which are 

 known as Phanerogams, to the great class of which the 

 fern is one, known as Cryptogams. The knowledge of the 

 process enables us to form a guess at the line of descent 

 of the flowering plants, thus for instance it tells us that 

 they have probably been evolved from fern-like plants. To 

 the professed botanist this speculation is of the greatest 

 value. He studies all plants, and it is this kind of 

 knowledge which enables him to classify them in a 

 rational manner. The subject cannot have this sort of 

 interest to the elementary student. I have therefore 

 determined to treat alternation of generation only from a 

 general point of view, as a remarkable form of reproduction, 



