TERM OF PLANT UFE. 19 



'15. The Latin name is always double; — generic and specific. Thus 

 Fragaria is generic, or the name of the genus of the plant, vesca is 

 specific, or the name of the species. 



76. A Species embraces all such individuals as may have originated 

 from a common stock. Such individuals bear an essential resemblance 

 to each other as well as to their common parent, in all their parts. 



77. For example, the white clover (Trifolium repens) is a species 

 embracing thousands of cotemporary individuals scattered over our hills 

 and plains, all of common descent, and producing other individuals of 

 their own kind from their seed. 



78. Varieties. To this law of resemblance in plants of one common 

 origin there are some apparent exceptions. Individuals descended from 

 the same parent often bear flowers differing in color, or fruit differing in 

 flavor, or leaves dififering in form, etc. Such plants are called varieties. 

 They are never permanent, but exhibit a constant tendency to revert to 

 their original type. 



19. Examples. Varieties occur chiefly in spedies maintained by cultivation, 

 OS tlie apple, potato, rose. Dahlia. They also occur more or less in native plants (aa 

 Hepatica triloba), often rendering tljo limits of the species extremely doubtfuL Thoy 

 are due to the different circumstances of climate, soil, and culture to which they 

 are subjected, and continue distinct only until left again to multiply spontaneously 

 from seed in thoir own proper soil, or some other change of circumstances. 



80. A <3bnus is an assemblage of species closely related to each oihut 

 in the structure of their flowers and fruit, and having more points of 

 resemblance than of difference throughout. 



81. Ilujstration. The genus clover (Trifolium) includes many species, as the 

 white clover (T. repens), the red clover (T. pratense), the buffalo clover (T. reflexum), 

 etc., agreeing in floral structure and general aspect so obviously that the most hasty 

 observer would notice their relationship. So in the genua Firms, no one would hes- 

 itate to include the white pine, the pitch pine, the long-leafed pine (P. strobus, 

 rigida, and palustris), any more than we would fail to observe their differences, 



82. Thus individuals are grouped into species, and species are asso- 

 ciated into genera. These groups constitute the bases of all the systems 

 of classification in use, whether by artificial or natural methods. 



CHAPTER II. 



TEKM OF PLANT LIFE. 



S8. Plant Life defined. The vital principle in the plant or its life 

 is known only by its effects. In the animal these eficcts are, in kind, 

 twofold, indicating two kinds of life, the organic and the nervous life. 

 In the plant the latter kind is wanting, and the sum of its vital pho- 

 nomena is popularly expressed in the one word, vegetation. 



