CHAPTER I. — CLASSIFICATION OF PLANTS. 267 



The relations of the different groups may be represented in 

 the descending scale as follows : 



Sub-Kingdom, 

 Series or Branch, 

 Class, 



Sub-Class 

 Order, 



. Sub-Order, 

 Family, 

 Tribe, 

 Genus, 



Sub-Genus, 

 Species, 



Race, Variety. 



In the classification of plants in a natural system, no one 

 character or set of characters can be relied upon to the exclusion 

 of the rest. The whole structure and development of the plant 

 should be taken into account, in assigning it to its place in the 

 system. It must not be understood, however, that all characters 

 are of equal value, for this is far from being the case. For exam- 

 ple, the numerical plan of the flower is of much more value in 

 classification than the shape of the petals, and the structure of 

 the pistil has more significance than the character of the stem, 

 whether it be herbaceous or woody. Moreover, the same char- 

 acters do not always have the same value in some groups that 

 they have in others. The shapes of leaves, for instance, in some 

 genera afford convenient and reliable means of distinguishing 

 species, while in others, these organs are so inconstant in form 

 as to be nearly worthless for the purposes of classification. In 

 general, however, it may be said that characters drawn from the 

 reproductive organs are of more value than those drawn from 

 the vegetative, and those derived from structure are of more 

 importance than those derived from the habits of the plant. 

 The Elm and the Nettle, for example, resemble each other in 

 important structural features, and belong to the same natural 

 order, but their habits are widely different, the one being a per- 

 nicious pasture-weed, the other, one of the most magnificent and 

 valuable of our forest trees. 



