INTRODUCTION 11 



copies of the same work are placed together. Works 

 on the same subject, as Gray's Botany, Wood's 

 Botany, Bessey's Botany are also placed in a larger 

 group. Then all the scientific books are formed into a 

 still larger group, as are the books of fiction, the books 

 of poetry, the music books and the like. Comparing 

 this arrangement with that employed in natural history, 

 each separate work, as Gray's " Manual of Botany," 

 Thomas' " Fruit Culturist," Bunyan's " Pilgrim's Prog- 

 ress," would correspond to a species, and the different 

 copies of the same work would correspond to individuals. 

 It should not be understood, however, that the several 

 species of plants and animals are always as readily distin- 

 guished as are the different works in a bookstore. The 

 books treating of the same general subject, as the different 

 works on geology, botany or arithmetic, might correspond 

 to genera, and the different classes of books, as scientific 

 books, books of fiction, would correspond to families. 

 There would also be copies of the same work in different 

 bindings, which might be said to correspond to varieties. 

 22. Scientific names are given to plants and animals 

 because the common names by which they are known are 

 so often local. For example, quack-grass, one of our 

 common troublesome weeds, is known by at least seven 

 different common names in this country alone, and yet, 

 in a given locality it is often known by only one name. Its 

 scientific name, however, Agropyron repens, is the same 

 in all languages and countries. Scientific names are 

 usually Latin and consist of two words. The first word is 

 the name of the genus to which the plant or animal belongs, 

 and is called the generic name ; the second word designates 

 the species, and is called the specific name. For example, 

 Pyrus malus is the scientific name of the common apple, 



