to another, in the same proportions as the Humber of species of a given 
family. 
B13 from Species or individuals of the same form, ae re-produce 
themselves in conformity fo certain fixed laws, we pass to those divisions 
of the natural system, which are abstractions of different degree of impor- 
ce, we may eithar confine ourselves to pee or order ctions of a 
sull higher degree. There are certain genera and fi adhe Which belong 
exclusively to certain zones, and a particu Mee CsAbBation of the conditions 
of climate; but there is also a a great number of genera and families, of 
‘which we find representatives tinder all zones anid at all elevations. The 
earliest researches upon the geographical distribution of forms ‘were those 
M. \Treviranus, published in his ingenious work on Biology, (vol. ii. pp. 
. AT, 63, 83, 129,) and the object of these was the stations of : genera upon the 
- globe. ut it is more difficult to obtain general results from such a method 
than from that which compares the number ots species of each family, or 
' the gteat groups of a particular family, to the whole mass of phaxnogamous 
Bs plants. In the frozen zone, the variety of genuine forms does not diminish 
eo oun anything | like the degree of decrement of species ; a greater number of 
4 spetonet ts a Mas number of species, is always to be found in such coun- 
t also is with the summits of high monntains, which are 
eBlottisad BY a ent number of genera su pplied. by the more abundant veg- 
Siation of the 
3 
A 
ment, ‘the elevation of each ant in more than 4, O00 Miuaee above the evel of 
- the sea in equinoctial America, it will be easy, when the account of the 
"species is completed, (it is si complet ed.) to separate those which crow at 
_ or above an elevation of 6,000 feet from such as are inhabitants of a lower * 
ae, —“Tegion. ‘This operation ht affect most sensibly those fan nilies ee abound 
. a alpine species; as, for instance, Graminee and Composite. At 6,00 
; ‘feet hi ‘Gameaek ‘the mean temperature of the air, on the back of the equa- 
t Andes, is 62° 6! which is equal to ‘that of July’ at Paris. “Although, 
poe tite tible- land of the Cordilleras, we find the’ sare annual tempera- 
tite’ as inthigh latitudes, yet it is not right’ to ina ot too much such 
alogies between the te i climates of equatorial mountains and low 
Stations in the circumpolar zone. ‘These iigiest ‘ere not so great as is 
; they are much influenced by the’ partial’ distribution of heat in 
* galiepent! seasons of the year. The bsnl des Not regularly change in 
‘rising from the plains into the mountains, in the same mariner as it does in 
“ “opriaching the pole’; as happens with: ‘Monocotsledones i in general, ferns, 
site. 
tn si rave ioe diver, remark, that the developtient ofthe vegetation of 
_ different families aesoniae neither upon geographical or isothermal latitude , 
lone ; but that, on the'<ontrary, the quotients are not in Amer on the 
a ze 
= . z : : ‘ 5 8] é zs [ 300 ] . 
+7 13 very i Fadeahie to study the vegetation of the tropics and of the 
* 
