CLASSIFICATION. 395 



examination of the germ would mislead us, for the coty- 

 ledons may be obsolete, as in Cuscuta, or united together, 

 as in Clintonia. Botanists therefore seldom actually refer 

 to the seed for such simple information. Certain other 

 characters of a plant are closely correlated with the number 

 of seed-leaves ; thus monocotyledonous plants almost 

 always possess leaves with parallel veins like those of 

 grass, while dicotyledonous plants have leaves with reti- 

 culated veins like those of an oak leaf. In monocotyle- 

 donous plants, too, the parts of the flower are most often 

 three or some multiple of three in number, while in dico- 

 tyledonous plants the numbers four and five and their 

 multiples prevail. Botanists, therefore, by a glance at the 

 leaves and flowers can almost certainly refer a plant to its 

 right class, and can infer not only the number of coty- 

 ledons which would be found in the seed or young plant, 

 but also the structure of the stem and the other general 

 characters and relations of a dicotyledon or a mono- 

 cotyledon . 



Any conspicuous and easily discriminated property 

 which we thus select for the purpose of deciding to which 

 class an object belongs, may be called a characteristic. The 

 logical conditions of a good characteristic mark are very 

 simple, namely, that it should be possessed by all objects 

 entering into a certain class, and by none others. The 

 characteristic may consist either of a single quality or 

 circumstance, or of a conjunction of such, provided that 

 they all be constant and easily detected. Thus in the 

 classification of mammals the teeth are of the greatest 

 assistance, not because a slight variation in the number 

 and form of the teeth is of any great importance in the 

 general economy of the animal, but because such variations 

 are found by empirical observation to coincide with most 

 important differences in the general affinities. It is found 

 that the minor classes and genera of mammals can be 



