V. INEQUALITIES OF DISTRIBUTION. 427 



no. 48, — iu the vegetal census, no. 56, — or even in the 

 series of average frequency, where it stands much helow 

 the medium. But such specialties belong rather to the 

 next and following sections of these remarks. 



5. Inequalities of Area and Census. 



1. Floral Diversities. — No two countries present the 

 same floras or the same vegetation. Alwaj'S there are 

 species in the one or other of them which are not found 

 in both. And if the floras of two small adjacent tracts 

 do happen to be nearly identical in regard to the species 

 which compose them, the vegetation of the two tracts will 

 certainly differ through inequalities of frequency among 

 the same species. The vegetal diversity may be deemed 

 a rule absolutely without exception, although more or 

 less wide according to special circumstances. And the 

 floral diversity is so usual that it also may be held a rule 

 almost equally true, and applicable to all except very 

 small and closely adjacent tracts. 



Floral diversity may be positive or negative. The 

 presence of certain species in one tract, which are not 

 found also in the other tract, is a positive character in its 

 flora. The absence of certain species from one tract, 

 which are found in the other tract, is a negative character 

 of its flora. The diversity between any two floras may 

 thus be positive in both ; or it may be negative on one 

 side and positive on the other side ; but it cannot be 

 negative in both. For instance, A and B have 1000 

 species common to both alike ; B having also 20 addi- 

 tional species not found in A. Here, the diversity be- 

 tween the two floras is negative in that of A, positive in 

 that of B. But if A could acquire any number of added 



