DEVELOPMENT OF PLANTS 133 



etc. The termination of phyta, from phyton a plant, distin- 

 guishes the division from the other groups. To repeat, the 

 division is composed of subdivisions which in turn are made up 

 of classes. Frequently the division contains only classes. Classes 

 consist of related orders. The orders are divided into families 

 which include allied genera and these latter groups comprise 

 closely related individuals or species. The vegetation of the 

 earth is separable into four widely differing divisions : I., The 

 Thallophyta, including among others the fungi and algae ; II., 

 The Bryophyta or moss plants ; III., Pteridophyta or fern plants ; 

 IV., The Spermatophyta or seed plants. The character and rela- 

 tionship of these groups will be considered in the following pages. 



