ANGIOSPERMS 441 



A . The Greatest Group of Plants. There is hardly need 

 to tell you what angiosperms are. You know that all 

 plants which have seeds inclosed in an ovary are angio- 

 sperms, and nearly all the plants with which you are familiar 

 have this character. Nearly all of the first part of this 

 book is devoted to angiosperms. Six chapters are given 

 to the description of the sporophyte generation of this 

 group of plants. All that has been said about roots and 

 stems -and leaves and about the life which goes on 

 in them, was based upon angiosperms. They are the 

 common, familiar plants. It is an angiosperm which comes 

 at once to mind when we hear the word " plant." The most 

 conspicuous, the most useful, and the most highly dif- 

 ferentiated of all plants, are the angiosperms. 



There is no need to describe again the nutritive body of 

 these plants, or the structure of the flowers which it bears. 

 With these you are familiar. It remains only to discuss 

 the relationships of the flower and those hidden repro- 

 ductive parts which you could not understand until after 

 you had studied the lower plants. 



B. The Flower. What is a flower ? It is a hard thing 

 to define. We may say that flowers are structures which 

 have evolved from strobili. They, like strobili, are groups 

 of sporophylls. Yet they are more than that. Flowers 

 have other parts than sporophylls. These other parts are 

 around the sporophylls, outside of them. They are usually 

 colored. They compose what is called the perianth. 

 With it you are already familiar. You know that it is 

 commonly composed of sepals and petals. Yet there are 

 some flowers, naked flowers, which do not have a perianth. 

 Such flowers are strobili and nothing more. They differ 



