Mr. R. B. Hinds on Geographic Botany, 



25 



18*8. Proceeding in the same manner to estimate the number 

 of species in each genus, they will be found to average upwards 

 of ten to each, or 10*6. As the value of the group or assemblage 

 depends on the amount of its component parts, so we must re- 

 gard the value of a natural family or genus as governed by the 

 number of its constituents ; 18*8 is then the average value of a 

 family, and 10*6 of a genus. 



A discrepancy of opinion is not unlikely to arise respecting 

 what should be considered as the division of the globe to which 

 a natural family belongs. Each of the latter is formed by the 

 aggregation of two classes of constituents, of different value and 

 number, these being inversely to each other. The genera, as 

 originating in characters of greater value, may on the one hand 

 be considered to determine this, and on the other the great nu- 

 merical proportion of species may be regarded as conclusive. 

 Many of the families which possess the greatest proportion in 

 one division are represented by a superior number of genera in 

 some other, where the amount of species is smaller; to which 

 then of the two does the group essentially belong ? In reply we 

 must confess that frequently it is extremely difficult to decide, 

 and in some cases altogether impossible, since the characters ap- 

 proximate so closely in value. An analysis of Byttneriacea will 

 more clearly explain this : if the number of species alone are re- 

 garded, the mass of the family is African, and afterwards South 

 American ; but if guided by the genera it is essentially Asiatic, 

 whilst Australia follows with very few species. 



Magnoliacece is another instance ; and in this case we can 

 hardly venture to say which of the two, Asia or North America, 

 claims it most forcibly. 



The native country of a family or genus is evidently an inap- 

 propriate expression ; it assumes that some of its members have 

 migrated from their original place of growth, a circumstance 



