MONOUOTY LEDONS 968 
are called species. Therefore, a group of related species 
forms a genus; and a group of related genera forms a family. 
An acquaintance with the plants of a neighborhood should 
begin by learning to recognize not merely important families 
but also conspicuous and common genera and species. 
The technical name of a plant is the combination of its 
generic and specific names, the former always being written 
first. For example, Quercus alba is the name of the com- 
mon white oak, Quercus being the name of the genus to 
which all oaks belong, and alba the specific name that 
distinguishes this oak from other oaks. No other names 
are necessary, as no two genera of plants can bear the same 
name, and no two species of a genus can have the same 
name. 
The so-called Manuals or Keys are books that contain 
descriptions of plants, so arranged that one who knows 
the meaning of the terms used can find the name of any 
plant described. Ability to use such a manual is very 
desirable to cultivate, for it is the most accurate and 
effective method of forming a speaking acquaintance with 
plants. 
156. Families of Monocotyledons.—About forty mono- 
cotyledonous families are recognized, containing numerous 
genera and about twenty thousand species. Four fami- 
lies will be selected, which include the great majority of 
Monocotyledons; and these should be recognized at sight. 
These families are conspicuous in numbers, or in appearance 
or in usefulness; and for any or all of these characters they 
deserve acquaintance. 
157. Grasses.—The Grass Family (Graminee) is one of 
the largest groups of plants. It is world-wide in its dis- 
tribution, and is remarkable in its display of individual 
plants, often growing so densely over large areas as to form 
a close turf. 
The flowers are very simple, having no calyx or corolla, 
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