CHAPTER X 



SUBDIVISION 2. ANGIOSPERMAE. PLANTS WITH ENCLOSED 



SEEDS 



122. Origin of the Angiospermae. — These plants, like the 

 Gymnospermae, produce seeds, but they differ so essentially from 

 the latter group in the character and structure of the sporophyte 

 and gametophyte as to justify their separation into a distinct 

 division. They are retained here as a group coordinate with 

 the gymnosperms out of deference to common usage. It has 

 been noticed that the seed habit arose quite independently of 

 the Spermatophyta (see page 336) and it appears more prob- 

 able that the Angiospermae have been derived from some extinct 

 seed-producing group of plants and have developed independently 

 of the gymnosperms. Though less ancient than the latter class, 

 their origin is still uncertain and the meagre evidence points to 

 their derivation from some primitive line of ferns rather than 

 from the higher pteridophytes or gymnosperms. The variations 

 of this modern group of plants have been many and so success- 

 ful that they have crowded out many of the lower forms and 

 become the dominant plants upon the earth. They exceed all 

 other groups combined in variety and number of species. Ap- 

 proximately, 125,000 species are known that are adapted by their 

 variations to practically all conditions that will sustain life, 

 ranging from aquatics to xerophytes, from terrestrial to epi- 

 phytes and from photosynthetic to saprophytes and parasitic 

 plants. The important features of the plant body have been 

 considered in the opening chapters of the book. 



123. The Sporophylls of Angiosperms. — ^The flower is often 

 considered as one of the most characteristic features of the 

 angiosperms, but this structure contains as its essential organs 

 one or more sporophylls and the term flower could be applied 

 quite as well to the association of these organs in the Pteridophyta 

 and gymnosperms. 



362 



