The Scottish Naturalist. 99 



intend by Definition ; and with this alone we shall at present 

 occupy ourselves. 



Now Definition, thus understood as dealing with the 

 " characters " of groups, is either of two kinds, according to the 

 object we have in view. If we intend simply to aid identifica- 

 tion, it will be sufficient to state the one or two leading 

 characteristics (such as are obvious and readily recognised) that 

 serve to distinguish one group from another ; but if we be guided 

 by scientific purpose, then something fuller and more ambitious 

 will be required. We shall have to exhaust the characters ; and, 

 in doing so, to attend to all the niceties that the subject-matter 

 admits of, and that the logic of method demands. The first of 

 these is indeed an affair of considerable importance, and ought 

 certainly to have attention bestowed upon it, and to occupy a 

 definite place in every text -book of botany ; but the difficulties 

 attaching to it are not great, and, as it possesses considerable 

 utility both to the teacher and to the learner, there is little risk of 

 its being neglected or inadequately handled. But the second is a 

 matter of no small difficulty ; and as it demands in whoever 

 atempts it the subtlety of the logician as well as the knowledge of 

 the expert, it is apt to create interminable embarrassment, and to 

 lead to very unsatisfactory results. 



Let us then concentrate our attention for a little on this latter, 

 and see what principles are implicated in the process, and how 

 best we may deal with the difficulties that crop up. 



Definition, as I have already said, has to do with the botanical 

 " character." Now, this word, even in botany, is a term of 

 equivocal import. It may stand for the single identifying 

 peculiarity of a group, such as the basal gland on the petal of a 

 Ranunculus, or the pair of opposite lines of hairs on the Ger- 

 mander Speedwell ; or it may signify the congeries of peculiarities 

 that a group possesses, and that need to be taken in their totality 

 before you can have the full meaning of the particular assemblage, 

 such as the five peculiarities of the class Dicotyledons — viz., 2 

 cotyledons, exorhizal germination, exogenous growth (carrying 

 with it the facts of distinct or separable bark and wood in 

 continuous rings), quaternary or quinary symmetry, and reticulated 

 venation ; or the corresponding five peculiarities of the Monocoty- 

 ledons. Perhaps little inconvenience arises in practice from this 

 double usage ; but to obviate all ambiguity, the word " mark " 

 might be employed to designate the sum of the distinguishing 

 features (in which case, instead of speaking of a class-character, 



