298 INTRODUCTION TO BOTANY 



thousand species, and some think this number too low. Added 

 to this fact of the large number of species is the fact that the 

 number of individuals of a species may often be enormous, as 

 in the common blue grass, oats, or corn, each species of which 

 consists of unknown millions of individual plants. 



The diversity of angiosperms hi chemical composition is 

 equally great. Some constitute our most important foods, 

 others produce a large part of our medicines, and others 

 produce substances so poisonous that they are feared by all 

 who know about them. 



282. Vegetative structures. The essential facts regarding 

 the ways in which angiosperms make and use their food mate- 

 rial have already been given (Chapter II and the following 

 chapters). There have also been abundant discussions to show 

 something of the variety of structures that plants of this group 

 exhibit when they grow under different circumstances, as in 

 the water, on especially dry land, and under extremes of tem- 

 perature. The ways in which different vegetative structures 

 are used as means of reproduction are presented in chapters 

 on roots, stems, leaves, etc. Reproduction by means of flowers 

 has also received some attention, but a further discussion at 

 this time will serve to connect the angiosperms with the pre- 

 ceding groups. 



283. The angiosperm flower. The name flower is some- 

 times used in speaking of the collections of sporophylls that 

 are seen in the cones of pines. In the angiosperms, in addi- 

 tion to sporophylls, there are usually other leaf-like organs 

 around the sporophylls, and the presence of these additional 

 floral leaves is popularly considered as essential to the flower 

 (figs. 9 and 102). These added floral leaves are usually colored, 

 often in very striking ways. There are angiosperm flowers 

 that do not have these added floral leaves, such flowers being 

 naked (fig. 104). No complete distinction can be made be- 

 tween the collection of sporophylls, which in the pines was 

 called a strobilus, and the collection which is commonly known 

 as a flower in the angiosperms. 



