216 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW, 
It seems to me, therefore, that the boundaries of the larger 
floras, the limits of the petty invasions and skirmishings which 
we see in the flower-world round Glasgow, and the range of any 
particular species, are all very much of the same nature, 
They are very rarely definite: there is a border or debatable 
land. To study them properly, a purely artificial system is 
perhaps best, Any attempt to make geological boundaries 
applicable to, say, the Potamogetons or the Chenopodiums, would 
ve absurd. The only convenient system generally applicable is, 
in fact, latitude and longitude, as has been, to my mind, most 
conclusively shown by Mr. C. B. Clarke.* 

1 Biologic Regions, Phil. Trans. Roy. Soc. London, Vol. CLXXXIII. 
(1892), p. 371. 
