370 IX. ORDINAL SUMMARIES. 



nearly the same as that for total Britain, under any such numerical re- 

 arrangement ; some of the slight changes made being attributable to 

 incomplete knowledge or to arbitrary distinctions by botanists, rather than 

 to true natural differences. Filices and OrchidacecB would aflford true 

 examples of difference. The former order has equal numbers on the two 

 sides of the island ; which is a relative predominance on the western 

 side, on account of the total western flora being rather smaller than the 

 eastern. The orchids decidedly predominate on the eastern side of 

 Britain, through the existence of several local species in the south- 

 eastern provinces of England, which do not extend into the western 

 division ; and the order would thus take a position relatively higher in 

 the one division than in the other. 



Considerably wider changes would be induced by a re-arrangement of 

 the orders according to the numbers stated in the second column. For 

 example, the numbers of Caryophyllacece and Juncacea run nearly uni- 

 form through the three latitudinal divisions; thus having a relative 

 increase in the northern division ; and the latter even an absolute 

 increase in that division, which has a considerably less numerous total 

 flora. On the contrary, Gramina lose nearly one-fourth, and Legumi- 

 niferm more than one-third of their numbers in the same direction ; the 

 full difference between the floras of the southern and northern divisions 

 being something more than a third less in the north. Such changes 

 would become much greater in a re-arrangement of the orders for the 

 three ascending stages of altitude. Saxifragacem would rise to be the 

 tenth order in the series for the uppermost stage ; while it would sink in 

 the lowest stage somewhat lower than its position in the series for total 

 Britain. Some orders, not very scanty in species, quite disappear in the 

 uppermost stage ; for instance, Chenopodiacea and Euphorhiacea. 



3. Climatal Census. — The six ascending or climatal zones, consti- 

 tuting the agrarian and arctic regions, were explained at some length in 

 volume first, pages 19 to 43, and illustrated more specially on pages 40 

 and 41. In the first of the three treble columns of this census, the 

 numbers fur Britain generally are set against those for the agrarian and 

 arctic regions, apart from each other. In the second and third columns, 

 the numbers are given for the six zones, three agrarian and three arctic 

 zones. In the second tabular series or census of orders, the apparent 

 influence of latitude was partially modified by that of altitude; and in 

 like manner the influence of elevation was altered somewhat by that of 



