COMMENTARY ON THE INTRODUCTION AND APPENDIX. Ixiii 
bility of Mr. Hemsley’s instituting a closer comparison between the Mexican Flora and 
that of some tropical region in the Old World presenting as rich and varied a vege- 
tation, and I indicated the British-Indian Flora as especially suitable, both on this 
account, and because the ‘Flora of British India’ was sufficiently advanced in 
respect of available published and unpublished materials to supply accurate data for 
such a comparison. And further it appeared to me that by availing himself, together 
with these materials, of the geographical data appended to every genus of phanerogamic 
plants contained in the recently-concluded ‘ Genera Plantarum,’ Mr, Hemsley might 
very greatly advance that most instructive branch of phytogeography which originated 
independently and coincidently in the minds of Humboldt and Brown, and to which the 
former gave the name of Arithmetice botanices. 
Messrs. Godman and Salvin cordially responded to my suggestion, and I feel sure. 
that the results embodied in the “ Statistics of the Phanerogamic Flora of the World” 
(Introduction, pp. ix—lxi) will be received with gratitude by all botanists as a very 
valuable supplement to a work that owes its existence to those naturalists’ travels, 
collections, learned labours, and munificence. 
The tables at p. xv and following of the Introduction are particularly valuable, 
and give information previously unattainable. ‘The areas compared are approximately 
within the same latitudes, 9° N. and 83°N., but separated by nearly 180° of longitude, 
the Asiatic in 70° to 95° E., the American 80° to 115° W. Each presents a hot, moist 
tropical, a temperate, and a frigid climate. It is impossible to find, in the Old and 
New Worlds respectively, two areas more similar as to physical features, or in which 
the vegetation of their respective continents is more fully represented; and yet the 
comparison of their Floras shows that, with an almost total diversity of species, genera, 
and of many natural orders, the proportion of monocotyledonous to dicotyledonous 
plants is nearly the same in each; that the number of natural orders is only 12 fewer 
in Mexico; that the number of species in each differs by only 2000 (11,626 in Mexico, 
13,647 in India); that the average number of genera in each order is nearly the same 
in each (11 in Mexico and 13 in India); that the average number of species in each 
genus even more nearly coincides (6:4 in Mexico and 6-0 in India) ; and, more singular 
still, that the percentage of endemic species in each differs by only 2 per cent. 
It is instructive to observe that these marked resemblances in proportions do not 
arise out of a resemblance in the elements from which they are derived; for, turning 
to the natural orders that contribute largest to the Flora of each area, they are very 
differently represented as to number of species in each. Composite, which take the 
first place in the Flora of the globe and of Mexico, are reduced to the sixth place in 
India. Leguminosee, which are second to Composite alone, are second in both Mexico 
and India; but Orchidew, which hold the third place in the world and in Mexico, are 
first in India; Rubiacew, the fourth in the world, are the seventh in Mexico and fifth 
in India; grasses are fifth in the world and in Mexico, but only third in India. 
