288 VIEWS, &C. PHYSIOGNOMY OF PLANTS. 



tiles even to a greater extent), increase more than mammalia in 

 advancing towards the torrid zone. We might be disposed 

 to believe, from Cuvier's investigations, that this ratio was 

 different in the earlier age of our planet, and that the number 

 of mammalia that perished by convulsions of nature was much 

 greater than that of birds. Latreille has shown the different 

 groups of insects that increase in advancing towards the pole, 

 or towards the equator, and Illiger has indicated the native 

 places of 3800 birds, according to the quarters of the globe; 

 — a far less instructive method than if they had been given 

 according to zones. We may easily comprehend how, on a 

 given area, the individuals of one class of plants or animals 

 may limit each other's numbers, and how, after the long- 

 continued contests and fluctuations engendered by the re- 

 quirements of nourishment and mode of life, a condition of 

 equilibrium may have been at length established; but the 

 causes which have determined their typical varieties, and 

 have circumscribed the sj^here of the distribution of the 

 forms themselves, no less than the number of individuals of 

 each form, are shrouded in that impenetrable obscurity which 

 still conceals from our view all that relates to the beginning 

 of things and the first appearance of organic life. 



If, therefore, as I have already observed at the beginning of 

 this illustration, we attempt to give an approximative estimate 

 of the numerical limit (" le nombre limite" of the French ma- 

 thematicians), helow which we cannot place the sum of all the 

 phanerogamia on the surface of the earth ; we shall find that 

 the surest method will be by comparing the known ratios of the 

 families of plants with the number of the species contained 

 in our herbariums, or cultivated in large botanical gardens. 

 As I have just remarked, the herbariums of the Jardin des 

 Plantes at Paris were, in 1820, already estimated at 56,000 

 species. I will not hazard a conjecture as to the number that 

 may be contained in the herbariums of England, but the great 

 Paris herbarium, which Benjamin Delessert with the noblest 

 disinterestedness has given up to free and general use, was 

 estimated, at the time of his death, to contain 86,000 species, 

 a number almost equal to that which Lindley, even in 1835,* 

 regarded as the probable number of all the species existing 

 " on the whole earth." Few herbariums are numbered with 

 * Introduction to Botany, 2nd ed. p. 504. 



