S76 Baron Humboldt on the Ld%v$ which ate observed 
perate zone, there are not so many as under the tropics : thek 
absolute number still diminishes as we advance toward the pole 
-but since the cold region^ for example Hapknd, produces spe- 
cies of Ferns which resist the cold better than the gTeat massi 
of phaenogamous plants, the Ferns, by the number of spe-^ 
cies, predominate more over the other plants in Lapland than ir> 
France or Germany. The numerical proportions presented in 
the table which I have published in my Prolegomma de Bistri-^ 
hutione GeograpJiica Plantarum^ and which appears again here' 
perfected by the great labours of Mr Robert Brown, differ en- 
tirely from the proportions given by an absolute comparison of 
the species which grow in the different zones. The variation 
>vhieh we observe in proceeding from the equator to the poles is 
not consequently the same in the result of the two methods. In 
this, two of the fractions used by Mr Browii. and myself are va« 
liable, since, in changing the latitude, or rather the , isothermal 
zone, the total number of phasnogamous plants is not seen to 
vary in the same proportion as the number of species which 
constitute the same family. 
When from species or individvals of the same form which > 
are reproduced according to constant laws, we pass to divisions 
of the naiu7‘al method, we may turn our attention to genera, to 
families, or to sections still more general. There are some ge- 
nera and some families which belong exclusively to certain zones,, 
to a particular association of climacteric conditions ; but there is a 
great number of genera and of families which have representatives 
in all zones, and at all heights. The first researches which have 
been made regarding the geographical distribution of forms, 
those of M. Treviranus, published in his ingenious work on 
Biology, (vol. ii. p. 47. 63. 83. 1^9.), have for their object the 
dispersion of genera over the globe. That method is less pro- 
per for presenting general results than this, which compares the 
number of species of each family, or the large groups of the 
same family, with the total mass of phaenogamous plants. Iri 
the frigid zone, the variety of generic forms does not diminish 
in the same degree as the variety of species : we find more ge- 
nera, with a smaller number of species, (Decandolle, TMoric 
Element, p. 190. ; Humboldt, Nova Gen. vol. i. p. xvii. & 1.)^ 
It is nearly the same on the summit of the lofty mountains^ 
