DEVELOPMENT OF PLANTS 141 



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 com- 

 prise closely related individuals or species. The vegetation of the 

 earth is separable into four widely differing divisions: L, The 

 Thallophyta, including among others the fungi and algae: IL, 

 The Bryophyta or moss plants; IIL, 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. 



