GENEEAL PEINCIPLES OP CLASSIFICATION 5 



a genus is defined as a collection of species which resemble each 

 other in the structure and general characters of their organs of 

 reproduction. It is not necessary, however, that a genus should 

 contain a number of species, for, if a single species presents 

 peculiarities of a marked kind, it may of itself constitute a 

 genus. 



It frequently happens that two or more species of a genus 

 have a more striking resemblance to each other in certain im- 

 portant characters than to other species of the same genus, in 

 which ease they are grouped together into what is termed a sub- 

 gcnus, and further subdivisions of more nearly allied species, 

 such as sections, sub-sections, &c., may be made. 



3. Oedbrs or Natural Orders. — If we regard collections of 

 genera from the same point of view as we have just done 

 those of species, — that is, as to their close resemblances, — 

 we shall find that some of them also resemble each other 

 more than they do other genera. Thus, Mustards, Turnips, 

 Eadishes, and Cabbages have a strong common resemblance, 

 while they are unlike Strawberries and Brambles, even less like 

 Hazels, Oaks, and Beeches, and still more unlike Larches, 

 Pines, Firs, and Cedars. Proceeding in this way throughout 

 the Vegetable Kingdom, we collect together allied genera, and 

 form them into groups of a higher order called Orders or Natural 

 Orders ; hence, while genera are ooUeotions of related species, 

 orders are collections of allied genera. Thus, Turnips, Radishes, 

 and Cabbages, all belong to different genera, but they agree in 

 their general structure, and are hence included in the order 

 Cruciferce ; while Strawberries, Brambles, Eoses, Apples, and 

 Plums, constitute different genera, but, from the general resem- 

 blance they bear to each other in their structure, they are placed 

 in one order, called Bosacece. Again : Oaks, Beeches, and Hazels 

 belong to different genera, but to one order ; also the Pines 

 and Cedars are different genera, but as the fruit of them all is 

 a cone, they are grouped together in one order, which is termed 

 the ConifercB. 



We find also that certain genera of an order, like certain 

 species of a genus, have a more striking resemblance to each 

 other than to other genera of the same order ; hence such are 

 grouped together into what are called Sub-orders. Thus the 

 Chicory, Dandelion, Sow-thistle, Lettuce, Thistle, Burdock, and 

 Chamomile, all belong to the same order, but there is a greater 

 resemblance in the Chicory, Dandelion, Sow-thistle, and Lettuce 

 to each other than to the Thistle and Burdock. Hence, while all 



