INTRODUCTION. Xxill 
is to be attached to the fact, it is remarkable and noteworthy, as a matter of figures, what 
a close approach there is to uniformity in the proportions in each of these four 
dissimilar and distant areas. Thus :— 
Average number of Genera Average number of Species 
to an Order. to a Genus. 
India. . . . . . . . 18:0 6:0 
Mexico. . .... . 110 «64 
N. America .. . ... 96 6°2 
Australia . . . .. . 87 6°4 
The proportions for the whole world, calculated from the numbers of the ‘ Genera 
Plantarum,’ are 37:50 genera to an order, and 12°65 species to a genus; from which it 
appears that there is, approximately, half of the average number of species of a genus, 
and a third to less than a quarter of the average number of the genera of an order in 
each of these large areas. Taking a portion of the Cape Flora, the average number of 
species to a genus is 6°6*; therefore between six and seven to one is probably the 
highest, or nearly the highest, average in large areas. Turning to other areas, the 
proportion of species is found to be much lower, and in certain insular Floras the 
genera are nearly as numerous as the species. In China the Polypetalous orders f 
yield about three species to a genus; and the proportions are nearly the same in the 
whole vascular plants of New Zealand, as well as in the Sandwich Islands. In Japan, 
the proportions are as 2°6 to 1; and of the probably endemic plants of St. Helena they 
are less than 1°4 to 1. . 
Such are the averages, which, as has been shown (vol. iv. pp. 212-217), are made up 
to a great extent by genera numerous in species and genera of one species each. In 
the Mexican Flora, for example, eighty-five genera contribute 4760 species, or 39 per 
cent. of the total, whilst other 660 genera are represented by only one species each, 
upwards of one third of them being absolutely monotypic. The composition of all 
large Floras, in which there is a high percentage of species to a genus, is similar ; whereas 
in the Chinese and Japanese Floras there are exceedingly few very large genera, and at — 
the same time a smaller proportion of monotypic genera. We have not counted the 
monotypic genera of the Indian Flora, but the proportions are probably very nearly 
the same as in the Mexican Flora. As mentioned elsewhere, Mueller { states that 
there are 550 genera in Australia represented by only one species. With regard to 
large genera in the Indian Flora there are only seven of 100 species and upwards each, 
against ten in Mexico and four § in Australia ; and there is nothing in either India or 
* Harvey and Sonder’s ‘Flora Capensis,’ vol. i, Ranunculacee to Connaracem, as estimated by 
Mr. N. E. Brown, in manuscript, in the Kew library. 
+ Forbes and Hemsley, “ Index Flore Sinensis,” Journ. Linn. Soc., Bot. vol. xxiii. 
+ Lecture on the Flora of Australia, 1883, p. 11. 
§ Six according to Mueller in the place cited, but he unites some genera retained by Bentham and Hooker. 
