156 BACTERIA IN RELATION TO PLANT DISEASES. 



with a particular organism by means of an author's description or figures or collected 

 specimens, then this name should disappear, never to be revived. Societies of 

 bacteriologists should unite in the near future on some authoritative date for the 

 beginning of species priority, so that some sort of stability may be guaranteed to 

 the nomenclature of the future. 



In the way of generic nomenclature there is not much of value prior to Cohn's 

 first great paper in the year 1872. It seems perhaps rather commonplace reading 

 now, but it really marked a great advance and was the result of twenty years of 

 diligent inquiry. Inasmuch as there is no present agreement among bacteriologists 

 as to the limits of common genera, the same genus name being used with very 

 different meanings by different writers, it appears worth while to discuss the subject 

 of genera at some length. 



At the outset three principal inquiries arise. First, what character or congeries 

 of characters shall be considered of generic value ; second, what generic names shall 

 be used ; third, what meaning shall be attached to these names ? 



In the description of species it is necessary to draw very largely upon physio- 

 logical characters, but it will not be disputed, I think (certainly not by naturalists), 

 that genera ought to be founded, if possible, entirely upon morphological characters, 

 in conformity with the usages of other branches of natural history. Physiological 

 characteristics may be used to help out our description of sub-generic groups, such 

 as the yellow Bacterium (Pseudomonas) group, the green-fluorescent Bacterium 

 (Pseudomonas) group, the hog-cholera group, the hay-bacillus group, the Proteus 

 groiip, the Tyrothrix group, the Urobacillus group, etc., but morphology appears to 

 be sufficient to distinguish the genera. 



Quite dissimilar organisms are still put by many writers under the same genus 

 name, but the tendency to carefully discriminate is on the increase, and before many 

 years, it is safe to say, writers on bacteria will be using generic names with a definite 

 morphological meaning. Certain it is that we can not go on much longer calling 

 any rod-shaped organism Bacillus or Bacterium interchangeably, or putting it into 

 the one genus or the other according as we happen or do not happen to find it 

 producing endospores, or growing as a short rod or as a filament. Some light may 

 come from considering with what meaning such generic terms were originally used. 

 Matters would also be much simplified by accepting 1872, the date of the appear- 

 ance of Cohu's first great paper, as the proper date for the beginning of generic 

 nomenclature of the bacteria, using only such earlier names as he accepted, emend- 

 ing his conception of these genera in such ways as experience has shown to be 

 necessary, and adding new names from time to time as new genera are discovered. 

 If some date is not settled upon in the near future, then we may expect an attempt 

 to substitute certain names which have not been at all used for the last thirty years, 

 i. e., since bacteriology became a science, for those which are now in common use. 

 The confusion which would result from an attempt of this sort and the utter useless- 

 ness of making such a change are sufficient grounds for desiring an authoritative 

 expression of opinion on the part of organized bodies of men cultivating this 

 branch of science before we are precipitated into any such confusion. The question 

 raised is this : Shall we abandon modern generic names given to definite, well-known, 

 and easily recognizable organisms for old names given before there was any science 



