BO TA NIC A L NOMENCLA TURK 225 



indicate actual errors. The lines of distinction Ix'twccn two f,fcncra 

 are often very ari)itrary, the different ()i)inions of different botanists 

 being apparently equally well founded. One botanist will thus regard 

 as of one genus plants which another divides among two or more genera. 



Another very common error in the past was that of assigning to a 

 genus a name which had already been applied to another. This, of 

 course, necessitates a re-naming of the genus, all the specific names 

 remaining unchanged and their autliors cited in ])arenthesis as already 

 explained. 



Errors in specific names have occurred most frequently through the 

 re-naming of a species which has already been published under a difierent 

 name. In such cases, when the error is discovered, the name last given 

 must fall. A difference of opinion has existed as to whether such a 

 discarded name should be permitted to be afterward taken up and 

 applied to a newly discovered plant. If the error in the first use of the 

 name were beyond question, no harm would result from so doing, but 

 such is not the case. In numerous cases botanists have disagreed as 

 to the specific identity of two plants. One regards one of the plants 

 as a mere accidental or temporary state of the other and discards its 

 specific name. If, now, the discarded name be applied to some other 

 species of that genus, there is danger that at any time the original 

 opinion may be revived concerning the previous application of that 

 name. This having in the meantime been applied to another si)ecies, 

 we have the same name applied to two species. For this reason conser- 

 vative botanists hold that just as a generic name once discarded may 

 never be given to another genus, so a specific name, once dropped, 

 may never be applied to any other species in the same genus. ' This 

 constitutes the important rule often referred to, as in the cxjjression, 

 "Once a synonym (or homonym) always a synonym." 



The whole subject of nomenclature and the rules which have been 

 formulated for it are very extended and c()mi)licated, but the most 

 important ])rinciples upon wliicli the rules are based have here been 

 explained. 



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