THK GKNUS ROSA 247 



separated by characters stable enough in themselves but 

 nevertheless of relatively minor importance, each form being 

 represented in any given station by crowds of individuals. 

 Furthermore, even in stations vastly different in geological 

 formation, there exist precisely the same types differing in the 

 saine way. For example, in two lanes in Mid-Durham on 

 the Coal Measures a certain variety of what I call Rosa omissa 

 occurs in hundreds. This is exceedingly closely allied to R. mollis 

 which grows alongside it. Twenty-five miles away on the 

 Magnesian Limestone of the coast denes identical forms of 

 both R. omissa and R. mollis abound, and the same holds 

 good of the Millstone Grit in Northumberland, thirty miles in 

 the opposite direction. In addition to this locality-constancy 

 both breed true to their special characteristics when due allow- 

 ance is made for variation, in response to environment, within 

 the limits of their particular range of fluctuating variation. So 

 true to type and its own range of variation is each of these 

 that knowing them only from these stations one could only 

 regard them as genuine Linnaean species. If, however, one 

 assembles with them numbers of similar forms from many 

 stations, near as well as far, one is driven to confess that they 

 merge* imperceptibly into each other as well as into many 

 types ot similar level, in this fashion forming alinked-up series 

 of groups with the individual members of the same group 

 substantially alike but each group separable from its 

 neighbours by its own special character or characters. 



Having thus equipped ourselves, and having submitted the 

 material to detailed examination, we realise at once that, 

 whilst we possess chains of groups continuous within the 

 limits of the chain, on the other hand each chain is definitely 

 divided from the next in respect to characters with which 

 the comparison which linked up the original groups into 



* It is well to emphasise here that, although, treated as above, all such 

 forms would yield a Quetelet curve, they do not pass into one another at 

 the minima of their respective curves ; they cannot by any possibility be 

 represented as a connected series of such curves. They are liable to 

 merge at any point and via any or all of their characters. , 



