Ill 



Mackaiana, Bab., lays claim to be a species distinct from E. 

 tetralixy Linn., from the midrib of the leaf and the sepals, 

 together with the ovary, being glabrous. 



The beautiful genus Erythraa affords a striking instance of 

 the slender and unsatisfactory characters it is sometimes neces- 

 sary to employ to distinguish nearly allied, though very 

 distinct, species. In this genus Britain is peculiarly rich, and 

 especially this neighbourhood, where all our native species 

 grow wild. But what are the describable characters by which 

 we can determine them? Only the relative length of the 

 teeth of the calyx. Now this character is most doubtful and 

 uncertain, and ought only to be relied on when all others fail ; 

 which we are bound to admit is the case in this instance ; 

 for although these species possess a peculiar habit and gene- 

 rally distinct appearance, it must be admitted that to the 

 present time all have failed in discovering any tangible charac- 

 ters. When comparing, a few months ago, numerous speci- 

 mens of this genus from this neighbourhood with plants in 

 the Smithian Herbarium, at the Linnean Society, I was very 

 much struck with the evident signs of labour Sir J. E. Smith 

 had bestowed upon the genus, to discover permanent characters 

 for the determination of the species. Babuglir, following 

 Smith after a long interval of years, lays great stress upon the 

 length of the calyx, which he states must be observed at the 

 time the flower opens. 



This character, conveying as it does rather an indefinite 

 idea, appears most unsatisfactory, and quite insufficient to dis- 

 tinguish one species from another; and it is only when the 

 plants are placed side by side that we see the difficulty in find- 

 ing words to convey an adequate idea of the distinctions then 

 so apparent, or how much more value is to be placed on the 

 habit of the plants than on anything else. 



From the variable nature of certain organs of vegetation, 

 which in certain tribes are so readily acted upon by the ia- 

 fluence of soil and climate, it is quite clear that we cannot 



