84 



SCIENCE. 



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



lated extra-limital species, is quickly seen 

 to be the merest artificiality. 



This introduces a subject which I would 

 earnestly emphasize, namely, that- those 

 who attempt to alter generic lines should 

 always take a broad, a cosmopolitan, view 

 of the group concerned. To do so, may, 

 it is true, involve great difficulty. It is a 

 relatively easy matter to divide into groups 

 two or three dozen species of any one of 

 the great genera like Euphorbia, Solanum, 

 Cyperus, Eupatorium, Polygonum or As- 

 tragalus. It is a very different task to 

 examine all known species of any of these 

 huge genera and show that they may be 

 divided into definable and mutually exclu- 

 sive groups ; but it should be perfectly evi- 

 dent that nothing short of a definite dis- 

 position of all the component species of a 

 genus can be construed as a satisfactory 

 and scholarly generic segregation. It 

 would probably be within the bounds of 

 truth to say that wide-reaching divisions 

 of large genera have within the last decade 

 been frequently undertaken without the 

 examination of more than a quarter or in 

 some instances a tenth part of the species 

 involved. Such attempts may be compared 

 if we return a moment to our marine simile, 

 to the guesswork of a negligent explorer, 

 who, finding an archipelago entered by a 

 deep inlet or bay, should, after sailing a 

 short distance into it, conclude that the 

 channel continued at the same depth and 

 in the same direction through the rest of the 

 group, and who should, therefore, record 

 such a clear channel on his chart, leaving 

 to future mariners who attempt to sail by 

 his map the unenviable task of discovering 

 by sad experience the real course and depth 

 of the channel. Neither such a chartog- 

 rapher nor such a botanist is likely to enjoy 

 long a reputation for accuracy or scholar- 

 ship. 



On the other hand, it may be urged, with 

 some plausibility, that many large and tra- 



ditional genera contain very unlike ele- 

 ments and that those writers who clearly 

 perceive this should not be obliged to 

 maintain the heterogeneous aggregate, even 

 though they may not be in a position to go 

 into the great task of examining all its 

 foreign representatives and deciding in 

 which component group each should be 

 placed. It may be argued, further, that 

 to impose such a burden of work as a pre- 

 requisite to every more sweeping generic 

 change would be to retard very greatly the 

 progress of classification. These, however, 

 are mere excuses for hasty and superficial 

 work. In fact, just such expressions as 

 'composed of very unlike elements' are ex- 

 ceedingly apt to be based on differences of 

 magnitude rather than those of constancy. 

 Persons examining our indigenous species 

 of Polygonum might very naturally sup- 

 pose the sections Persicaria and Avicularia 

 distinct genera. It requires a knowledge 

 of the Old World species to perceive 

 how untrustworthy are the distinctions 

 by which these subordinate groups are 

 separated. The caryophyllaceous groups 

 Alsine of Wahlenberg and Melandrium of 

 Rohling are commonly maintained as gen- 

 era by writers of central Europe and if 

 only European species are considered these 

 might seem fully worthy of generic rank. 

 It is after a study of Asiatic and American 

 species that the alleged generic distinctions 

 are seen to be weak and inconsistent. It is 

 an easy matter to separate sharply our few 

 species of Oxalis into groups on the basis of 

 homogony and heterogony, on the color of 

 the petals, and on the nature of the root- 

 stock. It is a very different task to ar- 

 range clearly in these proposed genera the 

 species of Africa, in which yellow petals 

 are sometimes associated with a bulbose 

 base and purple petals with elongated leafy 

 stems, in which heterogony bears no defimite 

 relation to color of petals, and in which 



