THE CLASSIFICATION AND NAMING OF PLANTS 327 
Moreover, every species belongs to a genus, every genus to a 
family, every family to an order or cohort, every order to a class, 
every class to a subdivision and every subdivision to a division 
or phylum of the Plant Kingdom. 
A GENUs is a group of related species. ‘Thus, the plants we 
recognize as red oak, scarlet oak, pin oak and white oak belong to 
the genus Quercus. The chief structure upon which the concept 
of a genus is based is the flower, but other organs also play a part. 
A FamIty is a group of similar and related genera. ‘Thus, the 
oak genus (Quercus), the chestnut genus (Castanea) and the beech 
genus (Fagus) constitute the family called Fagacee. 
An Orpber is a group of related families. ‘Thus, the Birch 
Family (Betulacee), the Hazel Family (Corylacee) and the Oak 
Family (Fagacee) constitute the order known as Fagales. 
It will be noted that the common family ending is ACEz&, 
more rarely 2 and the order ending ALEs. 
A Crass is a still higher group composed of related orders. 
Thus, the Fagales, Ranales and a large number of other orders are 
placed in the Class Dicotyledonez, because all of them have 
several outstanding characteristics in common, such as netted- 
veined leaves, two cotyledons in embryo, parts of their flowers in 
fours and fives, and open collateral bundles. 
A SuppIvision is a group of related classes. ‘Thus, the Class 
Dicotyledonez and the Class Monocotyledonez, while differing 
in several characters, resemble each other in possessing covered 
ovules and seeds and so are placed in the subdivision Angiospermae. 
A Division or PoyLum is composed of related subdivisions. ‘Thus, 
the Subdivision Angiosperme or related plants having covered 
seeds and the Subdivision Gymnosperme or plants with naked 
seeds agree in possessing seeds and so are placed in the Division 
Spermatophyta. 
- The Divisions Spermatophyta (seed plants), Pteridophyta 
(ferns and their allies), Bryophyta (liverworts and mosses) and 
Thallophyta (seaweeds, fungi, etc.) make up the Kincpom oF 
PLANTS. 
In some instances species are subdivided into smaller groups 
called Varieties and these in turn into SuB-VARIETIES, Forms and 
Strains. Classes may be subdivided into Sus-cLasses. Thus, 
the Class Dicotyledonee contains two subclasses, the ARCHI- — 
