396 X. GENERAL REMARKS. 



opposite direction, and in this mode to produce an inter- 

 mediate neutrality or equilibrium. For instance, in a 

 collective flora for total Britain we include about four 

 score species which are restricted to the most southern 

 portion of England, southward of the latitudinal line of 

 52 ; also nearly as many species which occur only in 

 Scotland. The inclusion of the former gives too austral 

 a character to the collective flora, and to the relative pro- 

 portions of its orders, &c. The inclusion of the latter 

 gives too boreal a character, in like manner. In the total 

 or average result these opposite excesses may nearly 

 balance one another. It takes a wider extent of the more 

 boreal latitude, to balance a smaller extent of the more 

 austral latitude ; because the total number of species 

 decreases in the northerly direction, as already shown by 

 the summary on page 364. 



4. Number of Species in proportion to Orders and 

 Genera. — Taking the list of genera and species, as made 

 out for the summary of distribution, and adding Gladiolus 

 thereto, the total flora of Britain wiU be found to exhibit 

 the subjoined numbers : — 



Orders, 98. Genera, 496. Species, 1425. 

 And converting these numbers into proportions, the 

 average number of sj)ecies will run thus : — 



To an order, 14.54. To a genus, 2.87. 

 Regarded in themselves, these are only isolated facts of 

 no import or importance. To give them significance and 

 value, they must be brought into juxtaposition with other 

 similar facts. First, how closely do these averages 

 represent those for portions of Britain ? If the three 

 latitudinal divisions be taken apart from one another, the 

 numbers may be stated thus : — 



