368 T. G. HALLE. [Nov. 1913. 



useful purpose, but a few of the points in question may 

 deserve some further consideration. i 



After quoting my opinion 'that it is a lesser evil to keep j 

 forms separated which are identical than to identify such as 

 are distinct' Prof. Sewakd argues as an antithesis that it is 

 a sound general principle 'to keep the mind open when there 

 is no sufficient warrant for closing it'. It is a strange illu- 

 stration of the difference in the conception of the problem 

 that this very principle is the first and chief reason also for 

 the exactl}^ opposite course advocated by the present writer. 

 Indeed, I believe that a brief consideration of the process of 

 classification of fossil plants will show the narrow delimita- 

 tion of species to represent the less committing way. 



The individual specimens constituting the material of the 

 palaeobotanist are grouped into species according to the degree 

 of morphological similarity — very much in the same manner as 

 in the classification of recent plants. There is the important 

 difference, however, that the palaeobotanical specimens, in the 

 overwhelming majority of cases, do not consist of individuals 

 but only of portions of such. Therefore different organs of 

 one individual may be referred to not only different species 

 but different genera, this being the rule in many groups. And 

 in cases of dimorphism, and even of great variation according 

 to position on the plant, different specimens of one and the 

 same kind of organ must often be described under different 

 specific names though they really belong to the same species. 

 These consequences, as every one knows, are unavoidable, being 

 with necessity connected with the nature of the palaeobota- 

 nical material. And they cannot be eliminated by means of 

 even the very broadest classification: there will always be 

 cases of dimorphism in which it is impossible to trace the 

 connection of the different t^^pes, and it is only exceptionally 

 that the material to be described is sufficiently large to give 

 a satisfactory idea of the range of variation of the species. 

 It follows, therefore, as a generally accepted fact, that the 



