196 INTRODUCTION TO BOTANY 



species that belong to it. A careful study of figure 164 will 

 give some notion of the relative resemblances of two struc- 

 tures in these six species of Quercus. In speaking of plants it 

 is customary to use both genus and species name (that is, the 

 binomial system of names), as Quercus alba; or, more often, 

 we use the common name, as white oak. Elementary botany 

 formerly concerned itself chiefly with attempts to learn the 

 genus and species names and the proper classification of seed 

 plants. We are now concerned more with how plants live than 

 with what their botanical names are. 



183. The leading groups of plants. Those genera (plural 

 of genus) which resemble one another are grouped together 

 into a family ; families with sufficiently close resemblances 

 are grouped into an order; orders are grouped into classes; 

 and classes into great groups. A study of the following divi- 

 sions of the plant kingdom will enable you to see the relations 

 that these divisions bear to one another, and the relations of 

 genus and species names to the whole plan of classification. 



Plant kingdom 

 Great groups 

 Classes 



(Sometimes sub-classes) 

 Orders 

 Families 

 Genera 

 Species 



(Sometimes varieties) 



The four great groups of plants are 



Spermatophytes, the seed plants in which are : 

 Angiosperms, or plants with inclosed seeds; 

 Gymnosperms, or plants with exposed seeds. 

 Pteridophytes, the fern plants, including the common ferns and other 



fern-like plants that are not so common. 

 Bryophytes, including liverworts and mosses. 



Thallophytes, including the lowest and simplest plants the fission 

 plants, the algae, and the fungi. 



Some of these groups will be very briefly considered in the 

 chapters immediately following. 



