100 SYSTEMATIC I'OMOhOGY 



tiiborous-rootcd plants, of wliidi the jjotato and dalilia are ex- 

 ainplcs. do not as a rnlc conu' true to seed l»nt aiT j)r()pa^'"at('d 

 by division of vcjifctativt' i)arts, — from euttin^^s, dons, buds, 

 offsets, bulbs, and tubers, — and are hence ealled vegetative 

 varieties. Differenees between vej^^etative vai-ieties seem to be 

 permanent tlirou^di lon^ series of {i:enerations. Heredity is ap- 

 parently eomi)lete in vegetative varieties, exeej)t in the rare eases 

 of bud-variations wliieh on trial prove to eome true as the nec- 

 tarine from tlie peach. 



\'arieties are the units in the classification of fruits just as 

 species are in botanical classifieation, with the advantage for 

 varieties that they are far less variable and do not shade off 

 from one form into another as do many species. Nearly all 

 varieties of fruits come from seeds, but rarely they arise as 

 mutations from buds, in which case they are called hud-varieties; 

 or more commonly among pomologists they are known as sports, 

 which is not so precise a term, as the latter may arise from seeds 

 as well as buds. 



143. Genera. — Just as individuals may be grouped in species, 

 so the latter may be put into more comprehensive assemblages. 

 Groups of closely related species form genera. Species are com- 

 monly brought together in a genus in accordance wdth similari- 

 ties in the form, arrangement, and number of parts of the flower 

 and fruit. The peach and common plum belong to distinct 

 species and differ from each other markedly in tree, leaf, fruit, 

 and in the size and color of their flowers, but the form, arrange- 

 ment, and number of parts of their flow'ers are so nearly alike 

 that the two species are put in the same genus by most botanists. 

 In some genera there are many species, in others few, and still 

 others are re})i"esented by only a single si)ecies. 



144. Orders, classes, and divisions of plants. — There are still 

 greater groups, more comprehensive assemblages, than genera. 

 Just as species are grouped into genera, genera in turn are 

 brought together in orders or families. In English parlance 

 family is preferred, as Family Rosaceas; popularly, a botanist 

 would write the Rose Family. Orders having characters in 

 common are assembled into Classes, and when classes have dis- 

 tinctive characters that are similar \h^y are finally grouped into 

 Divisions. 



