GEOGRAPHICAL DISTRIBUTION OF PLANTS. 519 
_ other, while countries situated under parallels very remote one 
_ from the other might have analogous climates. 
The travels of naturalists of our own day in all parts of the 
globe have established, to the satisfaction of botanists, that certain 
characteristics belong to the vegetation of each climate, contrasts 
attending which we shall endeavour to convey to the reader some 
succinct idea. - The researches of travellers, combined with the 
labours of descriptive botanists, enable us to give some precision 
to the principles of Botanical Geography. 
Let us establish, before going further, the approximate number 
of vegetable species which inhabit our globe. The appreciation 
of the statistics of plants is necessarily very varied in this sort of | 
estimate. Linneus, in 1753, was acquainted with 6,000 species. 
Persoon, in 1807, reckoned 26,000. In 1824 Stendel carried the 
number up to 50,000; and in 1844 to 95,000. The most recent 
works contain about 120,000 species. From the species described 
botanists have been able to form some approximate estimate of 
the total number of existing species. By an ingenious calculation 
of the space occupied by an average-sized plant, Alphonse de 
Candolle thinks he may infer that the“number cannot be less 
than from 400,000 to 500,000. 
We have said that in 1844 we knew 95,000 species of plants. 
Of this number 80,000 were phamerogams, or cotyledonous plants, 
15,000 were cryptogams, or acotyledons. Among the cotyledo- 
nous plants 6,500 belonged to the dicotyledons, and 15,000 to the 
monocotyledons. 
Such was the general budget of the terrestrial flora at this date. 
The numerical proportion of species belonging to the phanero- 
gams or cryptogams, varies according to the latitudes of the 
globe. As we advance towards the north, the number of crypto- 
gams increases; the number of phanerogams, on the other 
hand, increases as we approach the equator. In the frozen or 
temperate zones the cryptogamia are humble vegetables which 
scarcely raise themselves above the surface of the soil; but in 
the burning regions of the tropics, the elegant arborescent ferns 
rise to the height of the loftiest Palm-trees. 
. The vegetation of each species corresponds with a determinate 
interval in the scale of the thermometer, and this interval is not 
