82 



SCIENCE. 



[N. S. Vol. XXIII. No. 577. 



genius, so well known yet so variously used. 

 It is in no wise my purpose in the course 

 of these remarks to attempt to redefine the 

 generic concept, but merely to consider the 

 present divergence in the limitation of 

 genera and see if there is any practical 

 basis for a greater harmony in this matter. 



Plants are classified according to their 

 degrees of likeness or dissimilarity to each 

 other. In likeness we see evidence that 

 certain plants are related, and by related 

 Ave mean that they are sprung from a com- 

 paratively recent common ancestry. Like- 

 ness, it is true, no matter how close it may 

 be, is not an absolute proof of near rela- 

 tionship ; but, since in most cases it is im- 

 possible to trace conclusively the ancestry 

 of existing species of plants, their degree 

 of similarity furnishes almost the only evi- 

 dence available in regard to their relation- 

 ship. I need scarcely say that by likeness 

 is here meant not mere habital resemblance, 

 but the sum of all the morphological, 

 anatomical and physiological similarities 

 between the plants compared. Bearing 

 these matters in mind, we may roughly de- 

 scribe a genus (when pluritj^ic) as a 

 group of species which from likeness, ap- 

 pear to be more nearly related to each 

 other than they are to other species. But 

 so varying are the degrees of similarity and 

 so diverse is human judgment regarding 

 them, that such a definition offers only 

 an exceedingly vague basis for a uniform 

 classification. 



Indeed, the practise of different botan- 

 ists in the interpretation of genera has been 

 so multifarious that many persons have 

 become sceptical as to the real existence 

 of such groups in nature and are accord- 

 ingly inclined to treat the whole sub,ject 

 of generic classification as a mere matter 

 of utility, a sort of division of the plant 

 world into sections of convenient size' by 

 confessedly artificial lines analogous to the 

 parallels of latitude and meridians of longi- 



tude. But much may be said for the ob- 

 jective reality of genera, at least in certain 

 families. Who will wish to contend, for 

 instance, that such tolerably uniform 

 groups as Lupinus, Aquilegia, Delphinium 

 or Carex are not far more distinct natural 

 categories than are many of the relatively 

 vagTie and ill-defined species of which they 

 are composed. There can be no doubt 

 whatever that in many families clearly 

 definable genera exist and have been duly 

 recognized. In other families or parts of 

 families, however, the living species do not 

 fall into sharply limitable groups, but are 

 by character either somewhat isolated or 

 more often exhibit highly complex cross 

 affinities rendering any simple or convin- 

 cing classification into genera impossible.. 

 It is in such groups that uniformity of 

 classification is most difficult to obtain, for 

 it is in them that individual judgment has 

 the widest play. 



There are two very different methods of 

 treating genera. One is to lay much-stress 

 on the idea of a generic type, that is to 

 say, a species of the genus in question, 

 which is supposed to fix the generic char- 

 acter and pass as a sort of sample or gauge, ■ 

 by comparison with which other nearly re- 

 lated species are to be judged. If they 

 appear to agree with this type-species in 

 the essential characters, namely in those 

 points which in the particular family con- 

 cerned have come through accumulated ex- 

 perience to be considered of generic value, 

 the species are considered congeneric with 

 the type and receive the same generic name. 

 The other mode of treating a genus is to 

 endeavor not so much to group the species 

 about some historic type as to indicate the 

 precise circumscription of the genus by 

 pointing out as clearly as possible just how 

 its species as a whole differ from those of 

 related genera. A species has sometimes 

 been not unaptly referred to as an island 

 in a sea of death. Carrying out this simile 



