IV. VEGETATION OF BRITAIN. 423 



littoral species ; a third may be deemed sub-maritime, 

 especially in its more northerly provinces. These cha- 

 racters of place and conditions of growth must somewhat 

 keep down the census of those three species, when based 

 on the vice-comital sections ; some of which are quite 

 inland, and others including few places suitable for the 

 first and third species. Nevertheless, the average fre- 

 quency for the six species of this order rises to the high 

 figure of 78 ; and in this respect it is exceeded only in 

 two orders, Oxalidacete and Portulacece, each represented 

 by only a single sj)ecies. AraliacecB and Urticacece are 

 nearly the same, their averages being 78 and 77 repeti- 

 tions for a species. These high averages quite accord 

 with the great prevalence of plantains, ivy, and nettles in 

 the vegetation. Their paucity of species must prevent 

 those orders being absolutely predominant in the vegeta- 

 tion, as compared with grasses and composites, or catkin- 

 bearers and umbellates. But if compared with some 

 other orders, more equal to them in species, it becomes 

 evident to the observant British botanist, that they have 

 a decided tendency to become predominant in the vegeta- 

 tion, as much as the limited number of specific forms 

 may permit a predominance. Three quartets of orders 

 may be compared ender this view : — • 



Plantaginaceoe, 78. Urticaceae, 77. Araliaceae, 78. Oxalidaceae, 84. 

 Lycopodiacese, 43. Linacece, 47. Rhamnaceae, 46. Aiaceae, 43. 

 Pinguiculaceae, 34. Cistaceae, 10. Cornacece, 32. Santalaceae, 19. 



Such wide differences of average as are shown between 

 the first and third lines do not appear between the larger 

 orders ; because these latter mostly include both rare 

 and common plants, and their averages consequently tend 

 towards a medium figure between the two extremes ; 

 although, under special circumstances, considerable dif- 

 ferences are found between orders numerous in species. 



