322 PRACTICAL BOTANY 



294. The youngest and most successful group. As a group 

 these are the youngest plants. Even within the fossil beds in 

 which gymnosperms are abundantly represented there appear 

 few structures that can be interpreted as belonging to the an- 

 giosperms. Geologically the angiosperms are of recent origin. 

 The pteridophytes and gymnosperms in their periods of great- 

 est luxuriance comprised many diverse forms and many indi- 

 viduals. In the present age it seems that we are witnessing 

 the ascendancy of the highest and most successful plants. 



295. The most complex group of plants. In Chapter II 

 there were outlined the leading facts regarding the way in 

 which angiosperms are nourished and in which they repro- 

 duce themselves. In subsequent chapters many details were 

 given upon these two aspects of the work of plants. It has 

 certainly been made evident that the structure and habits of 

 life of angiosperms are complex, and enable them to live 

 under a very wide range of conditions. There are genera and 

 species of angiosperms some of which are able to live in almost 

 any kind of environment in which plant life is possible. 



The reproductive structures of angiosperms have much to 

 do with the success of the class. Many other features of the 

 group are of such importance as to demand an entire chapter, 

 and these are fully discussed under separate chapter headings 

 (Chapters II-IX, and XX-XXVI). Certain details of seed 

 formation and the relations that angiosperms hold to other 

 groups are presented in this chapter. 



296. The angiosperm flower. Collections of sporophylls such 

 as were seen in the pines are sometimes called flowers. In the 

 angiosperms there are usually leaf-like organs about the spo- 

 rophylls, and the presence of these is popularly considered as 

 essential to the flower. These leaves or bracts are not neces- 

 sarily colored, and indeed often are not so. Furthermore, 

 there are angiosperm flowers that do not have floral leaves ; 

 consequently no closely drawn line can be placed between the 

 strobilus, or cone of gymnosperms, and the flower of angio- 

 sperms. The essential structures of a flower are stamens or 



