rV. VEGETATION OF BRITAIN. 417 



the relative places of plants, in the scale of size, were 

 found to be so uncertain in many individual instances, 

 that it is doubted much whether botanists in different 

 countries would ever bring out results fairly comparable 

 with each other, by this laborious process. And if not 

 comparable, they would be useless. 



The uncertainty arises out of the wide dissimilarities 

 between plants, in their general appearance and mode of 

 growth. There is no doubt or difficulty in deciding that 

 a Plantago is larger than a Pinguicula, — that Hottonia is 

 larger than Utricularia, — that Convolvulus sepium is 

 larger than Convolvulus arvensis, — that Arundo Phrag- 

 mites is larger than Phalaris arundinacea, — that Polysti- 

 chum angulare is larger than Blechnum boreale, — that 

 Juniperus communis is larger than Calluna vulgaris, — 

 thaiFagus and Ulmus are larger than Alnus and Corylus ; 

 and so on, with respect to very many other British plants, 

 when thus placed in pairs of similar character and growth. 

 And it is easy enough to form ascendmg series of a dozen 

 or a score of species, thus mutually similar and com- 

 parable. But how to compare sizes between plants very 

 dissimilar, is the real difficulty. How to compare a 

 Carex with a Plantago, — a Juncus with a Carduus, — an 

 Orchis with a Potamogeton, — an Equisetum with a Lyco- 

 podium, — the Ferns with the Grasses, — slenderly erect 

 plants with tufted or creeping kinds ? 



It seems then, that repetitions of species must be 

 taken, apart from their dimensions, as the only prac- 

 ticable measure or test of ordinal predominance in the 

 vegetation ; subject to the interfering alternative, that 

 comital repetition may signify either a gi-eater frequency 

 or a wider area. In a serial or progressive arrangement 

 of the orders under this test, one slight modification may 

 be advantageously made, by grouping them according to 



VOL. IV. 3 u 



