98 SCIENCE PRIMERS. [xxv. 



to which its terms are applied. For this purpose 

 Latin and Greek are much used, because they are 

 acquired by educated peo'ple in all civilized countries, 

 and because they lend themselves by their flexibility 

 and harmonious sounds to the compounding of 

 names. 



148. The names in constant use for the purpose 

 of the classification of the members of the vegetable 

 kingdom are individual, variety, species, genus, order, 

 class, sub-kingdom. When referring to a plant, its 

 generic and specific names are both used, putting 

 the generic first if the Latin language is used, and 

 the specific first if the English (as Rosa canina, Dog 

 rose). 



A species is an aggregate of individuals which 

 have been proved to have descended from a common 

 ancestor, or are so similar to one another that they 

 may be presumed to have done so. But as no two 

 individuals are exactly alike, and as the number of 

 instances of unlikeness to the parent form increase 

 with the number of individuals produced by seed, it 

 becomes often difficult to define the limits of a species. 

 These unlike individuals are called varieties (Par. 

 150); and the descendants of a well-marked variety 

 that propagates its peculiarities with much constancy 

 by seed is called a race, and sometimes a sub- 

 species. 



A genus is an assemblage of species resembling 

 one another in most important points of structure, as 

 the various kinds (species) of oak, elm, willow, &c. 



Orders, also called Families are assemblages of 

 genera agreeing in certain marked characters. These 

 agreeing characters are sometimes obvious to the com- 



