" VARIETY" IN SYSTfiMATlCS. 123 



apparently established. .As said above ; geographical changes of an 

 abrupt type are probably caused by isolation of lines. The result 

 of isolating lines is well seen in the cultivated cereals. In natural 

 conditions isolation is much less frequent ; in fact it would not be 

 too much to say that Nature abhors a pure line, just as she abhors the 

 inter-specific cross. And it is these two facts alone which secure the 

 stability and continuity of the Linna^an species. Nevertheless varieties 

 due to isolation of lines without geographical isolation almost certainly 

 do occur, — -for instance Scirdus supinus var. imiondis Cke, and 

 Cyperus lria var. panicifonais Cke. 



Sixthly there are the not infrequent cases of species and genera 

 which are in an active staterof evolution, producing a maze of forms 

 among which clear specific lines of demarcation are not discernible* 

 These forms may be the De Yriesian mutants. It would be beyond 

 the scope of this paper to discuss this point ; but it is necessary for the 

 argument to say that whereas " lines " seem to be the product of 

 isolation and combination of already existing, stable allelomorphs, 

 the changing evolutionary forms now referred to would seem to be 

 caused by instability of the allelomorphs themselves, which in such 

 cases are disappearing and reappearing with changed properties. 



Seventhly (although they stand on quite a different footing) it 

 is necessary to refer to inter-specific hybrids, which though normally 

 abhorred by Nature, do occur, and will ultimately be detected in 

 India as they have been in Europe. 



Now, omitting hybrids, our floras have for the most part in the 

 past called all these varied forms of whatever origin by the one word 

 variety. It is true that in cases of species with a very great range 

 of variability the forms have sometimes not been given a varietal 

 name, but simply listed under numbers or letters. But it would 

 appear that this has been due more to convenience than to a clear 

 discernment of the different phenomena. 



Before considering the use of terms for units below the species 

 it is desirable to consider whether we are justified in using the same 

 term " species", undifferentiated, for the Linnaean group of individuals 

 in which the allelomorphs are stable as well as for those in which 

 they are unstable. The writer would suggest that the two pheno- 

 mena be distinguished as " species (constaus) ", and " species incon- 

 stans ", omitting in practice the word constaus. 



For units below the species the following scheme is suggested : — • 



A. For freaks or sports no special term, each one to be separately 

 described. 



B. (1) For geographical forms, where sharply distinguishable, the 

 trinomial system now used by ornithologists. 



