CLASSIFICATION. 119 



jectiag the plant often to conditions abnormal to it) in 

 producing monstrosities, sports, races, and varieties (in the 

 sense understood by gardeners) is very marked. Thus, 

 there are hosts of forms of the Dahlia in cultivation, all 

 derived since 1802 from Dahlia variabilis; the Pansies, 

 from Viola tricolor, are also numerous; "some Melons are 

 no larger than small Plums, others weigh as much as 66 

 pounds ; one variety has scarlet fruit, another is only one 

 inch in diameter, but three feet long; one variety can 

 scarcely be distinguished externally or internally from 

 Cucumbers ; one Algerian variety suddenly splits up into 

 sections when ripe." 



151. The several species of Willows have a marked 

 resemblance to each other: the same maybe said of the 

 various Oaks, Osiers, Clovers, Violets, etc. A group of 

 such nearly-related species is designated by the word 

 genus. Thus, there is a genus of Oaks ( Quercus), a genus 

 of Roses {Bosa), a genus of Toad-stools {Agaricus), a 

 genus of Busts {Puemda), and so on. The genera includ- 

 ing the Bean (Phaseohis), Pea {Pisurri), Vetch {ViekC), 

 Liathyrus {Lalhyrus), and several others, have a general 

 resemblance in foliage, flowers, fruit, etc. ; and they are, 

 therefore, grouped together, and constitute a family, 

 called, in this case, Legwninosae. Others, as the Iron- 

 weeds [Vernonia), Thistles {(Xrsium), Dandelion (raroso- 

 cum), Hieraeium, Laduea, etc — characterized by having the 

 flowers in an involucrate head with syngynesious anthers — 

 form the family CompodtoB. In like manner, that is, by 

 more or less closely related genera, other families, as 

 ManunGidaceoB, CnidfenB, Lahiatce, Grraminem, etc., are 

 formed. Larger groups, or orders, are formed of families, 

 and still more comprehensive are the sa-called classes. 



