THE FLOWER 211 
THE CLASSIFICATION OF PLANTS 
In dealing with the very large number of plants that occur 
in the world it is necessary not only to have names for the va- 
rious species but also to have a system of classification that 
groups plants together according to their similarities and rela- 
tionships. The different kinds of plants are regarded as differ- 
ent species, and each kind is given a species, or specific, name. 
The structure of the flower is the most important criterion in 
the classification of flowering plants. 
_ In classifying plants the different kinds (species) are grouped 
into genera, families, orders, classes, and divisions. The whole 
plant kingdom is divided into divisions, one of which, the Sper- 
matophyta, includes all seed plants. Divisions are subdivided 
into classes. The classes of the Spermatophyta are gymnosperms 
(seed plants without flowers in the popular sense) and angio- 
sperms (flowering plants). The monocotyledons and dicotyledons 
are subclasses of the flowering plants. An order isa large group 
which includes plants that have some prominent characteristics in 
common and show a natural relationship to each other. An order 
includes one or more related families. A family is therefore a 
subdivision of an order and consists of a group of closely re- 
lated genera, although a family may contain only a single genus 
if this genus is distinct enough from all others to be put into 
a separate family. Usually, however, there are a number of 
genera in each family. A genus is commonly a group of closely 
related species, but may contain only a single species. A spectes 
represents a single kind of plant, the individuals of which differ 
from each other only in minor characters which are bridged over 
by intermediate forms, and in characters which are due to age, 
sex, nutrition, individual peculiarity or accidents, or selective 
breeding by man. The individuals of a species may be cross- 
pollinated and reproduce the same kind of plant. 
The species, genus, family, and order have each a separate 
name. In writing the name of a plant we use the generic and 
the specific name. The generic name is written first and then 
