FORM AND STRUCTURE 
older, in others they persist. The best opinion now is that 
they are openings for the purpose of admitting air to the 
living internal tissues. 
SPECIES AND GENUS. 
Under the term Species are included all individuals which 
possess in common such a number of constant characters that 
they may be considered to be descended from a common an- 
cestral form. In the course of multiplication new peculiari- 
ties may arise and individuals characterized by these peculi- 
arities are regarded in classification as Varieties. 
When several species resemble each other so distinctly 
that their general characters indicate relationship they are 
grouped together in a Genus. Genera are not fixed, they 
vary with the views of botanists. 
The Scientific Name of a plant consists of two words, the 
first indicating the genus, the second the species. If a thira 
is added it indicates the variety. 
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