20 



MiLtahility and Individual Variation. 



true units. It seems that Linnaeus himself was fully 

 aware of the fact, but it is certain that it was gradually 

 lost sight of by his followers. In relatively few cases 

 did he himself distinguish varieties within his species, 

 and it is well known that when he did they were often 

 raised to the rank of species by those who followed him. 

 Well-known examples are afforded by Primida veris L. 



with the three varieties vid- 

 garis (acaulis) (Fig. 2), cla- 

 tior and officinalis ^ which 

 are now universally re- 

 garded as species solely on 

 the authority of Jacquin 

 without any further justi- 

 fication. In like manner 

 Lychnis dioica L. split up 

 into L. diiirna and L. vcs- 

 pcrtina, Platanthcra bifolia 

 L. into P. bifolia and P. 

 chlorantha and so forth. 



Numerous examples of a 



similar kind will occur to 



the reader. Conversely also Linnean species have been 



degraded to the rank of varieties : for example the Index 



Kewensis which recognizes the Primula species of Jac- 



^ Primula acaulis is distinguished from the two other subspecies 

 by the fact that its flowers arise singly by their stalks from the axils 

 of the leaves and are not united to form an umbel. This species 

 occurs in certain localities in the Netherlands, in the wild state, and 

 from time to time bears umbels of which one is drawn in Fig. 2. 

 Such cases are regarded as atavistic, as reversionary to some common 

 ancestor of those Primulas which still possess umbels. But this atav- 

 ism is not considered by the best systematists as sufficient ground for 

 re-constituting P. acaulis as a variety and the main species P. veris as 

 a species, in systematic works. From the point of view of the estima- 

 tion of the systematic value of Atavism in general this case evidently 

 is of much importance. 



Fig. 2. 



An umbel of Primula 

 acaulis. 



