Pa Se, eee tl ie 
ee Dr. G. a thon Eieeh bei 
897] 
BRLEPER ARTICLES. 
DEFINITENESS OF VARIATION, AND ITS SIGNIFICANCE 
IN TAXONOMY.' 
In descriptive and systematic botany we have just two things with 
which to deal, types and variants. The types are the comparatively 
absolute standards by which we measure the variations; but the variants 
occupy most of our attention. The type is the one fixed point for 
each species, while the limitations which we fix for the species repre- 
sent the extent of possible (permissible) variation from the type as 
determined by our arbitrary species measure. The ideal way to study 
systematic botany would be to keep the types always before us, and to 
describe each specimen by computing its variation from this or that 
type. This is, in fact, what critical study amounts to. In other words, 
the systematist is always measuring and classifying variations. If, 
therefore, definite lines of variation can be traced, it ought to be a 
matter of great convenience. 
The two opposing schools of evolutionary philosophers are divided 
at present as to whether variations actually do occur in definite direc- 
tions or not. But even Weismann? wrote in 1875, perhaps before he 
was so strongly confirmed in his present position, ‘the evolution of 
the species of Deilephila shows that the evolution of the marking fol- 
lows throughout a certain law; that it proceeds in all species in the 
same manner. All species seem to steer towards the same point, and 
this gives the impression that there is an internal law of evolution 
which, like an impelting force, determines the future yee modifi- 
cation of the species.” 
| The Neo Leaanckine are very” positive. on this point. Eimer? 
says “TI have, from the zoological standpoint, pointed out and emphat- 
ically maintained that the variation of species takes place, not in all 
__ directions irregularly, but dense in definite directions ; and indeed in 
ry 6, 1897. 
ICA ae Ue Cr ges c +h Vv mont Botanica! Cub, F 
d by Eimer, Organic Evolution, Ens. Eda 73 
