GENERA AND ORDERS. 359 



the various species of Roses and Sweetbriers ; the Bramble genus, 

 comprising Raspberries, &c, is popularly distinguished to a cer- 

 tain extent ; the Oak genus is distinguished from the Chestnut and 

 the Beech genus, &c. : each is a group of species whose mutual 

 resemblance is greater than that of any one of them to any other 

 plant. The number of species in such a group is immaterial, and 

 in fact is very diverse. A genus may be represented by a single 

 known species, when its peculiarities are equivalent in degree to 

 those which characterize other genera, — a case which often occurs ; 

 although if this were generally so, genus and species Avould be 

 equivalent terms. If oidy one species of Oak were known, the Oak 

 genus would have been as explicitly discerned as it is now that the 

 species amount to two hundred ; it would have been equally distin- 

 guished by its acorn and cup from the Chestnut, Beech, Hazel, &c. 

 Familiar illustrations of genera in the animal kingdom are furnished 

 by the Cat kind, to which belong the domestic Cat, the Catamount, 

 the Panther, the Lion, the Tiger, the Leopard, &c. ; and by the 

 Dog kind, which includes with the Dog the different species of 

 Foxes and Wolves, the Jackal, &c. The languages of the most 

 barbarous people show that they have recognized such groups. 

 Naturalists merely give to them a greater degree of precision, and 

 indicate what the points of agreement are. 



699. If all' such groups were as definite and as conspicuously 

 marked out as those from which illustrations are generally taken, 

 genera might be as natural as species. But unfortunately the pure- 

 ly popular genera are comparatively few, and although often cor- 

 rectly founded by the unscientific, j r et they are as frequently wrongly 

 limited, or based upon fanciful resemblances. Popular nomencla- 

 ture, embodying the common ideas of people, merely shows that 

 generic groups are recognizable in a considerable number of cases, 

 but not that the whole vegetable or the whole animal kingdom is 

 divisible into a definite number of such groups of equally or some- 

 what equally related species. "Whether this proves to be so or not, 

 and Avhether genera are actually limited groups throughout, this is 

 not the place to consider. Suffice it to say, that there is a ground 

 in nature for genera, and that the naturalist is obliged to treat them, 

 for systematic purposes, as strictly definite groups of species. "While 

 ge/uera represent the closer relationships of species, 



700. Orders or Families .(as they are interchangeably called in 

 botany) express remoter relationships or more general resemblances. 



