GENERA AND ORDERS OR FAMILIES. 353 



separate genera. The languages of the most barbarous people 

 show that they have formed such associations. Naturalists merely 

 give to these generalizations a greater degree of precision, and 

 endeavour to indicate what the points of common agreement are. 

 A single species, also, may be deemed to constitute a genus, when 

 its peculiarities are equivalent in degree to those which charac- 

 terize other genera, a case which often occurs. If only one 

 species of Oak were known, the Oak genus would have been as 

 explicitly recognized as it is now that the species amount to two 

 hundred ; it would have been equally distinguished by its acorn 

 and cup from the Chestnut, Beech, Hazel, &c. A genus, then, is 

 a group of species which present the same particular plan, and 

 whose mutual resemblance is greater than that of any one of them 

 to any other plant. 



673. When two or more species of a genus resemble each other 

 in particular points more nearly than they do the other species, 

 intermediate sections are often recognized ; which, when marked 

 by characters of considerable importance, receive the title of 



SUBGENERA. 



674. Orders or Families, If the genera were few, there would be 

 little necessity for higher generalizations ; although one could not 

 but remark that the Oaks, Chestnuts, Beeches, and Hazels have a 

 strong common resemblance, or family likeness ; and that they are 

 more unlike Birches and Alders, or Walnuts and Hickories ; that 

 they are still more unlike Maples or Ashes, and have yet fewer 

 points in common with Pines and Firs. But, since the 100,000 

 species of known plants are distributed among nearly 8,000 gen- 

 era, it is necessary to consider these family resemblances, for the 

 purpose of grouping the genera into still higher, and therefore few- 

 er, groups ; just as genera are formed by the reunion of related 

 species. The groups thus established are termed FAMILIES, or 

 ORDERS (names which are for the most part used interchangeably 

 in botany). Thus, the Rose, the Raspberry and Blackberry, with 

 the Strawberry the Apple, the Thorn, the Plum and Cherry, &c., 

 all agreeing in their general plan of structure, are brought together 

 into one order or family, and termed Rosacece ; that is, Rosaceous 

 or Rose-like plants. 



675. But, viewed subordinately, the Plum and Cherry are evi- 

 dently more nearly akin than the Cherry and Apple, &c. ; and so 

 the Raspberry, Blackberry, and Strawberry on one hand, and the 



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