[ 300 ] 82 
* 
plicated conditions of climate, but also upon geological causes, cig nature 
whi 
of which is wholly unknown, but which are connected with the original 
is of our planet. In the equinocta zone of Africa palms are not very — 
“numerous, if compared with the creater number in South America. 
Differences such as these, far trom t bipatio us from a search after the laws 
of nature, should, on the contrary, ae us to contemplate those laws in 
t ost complicate orms. Lines of equal heat do not follow the paral- 
lel of the equator ; they have saver and coneave su s, which are dis- 
cor ech examined, it will be found that the lines of mazima of grouping 
Sac is, lines drawn through those points were the fractions are reduced to 
the smallest denominator) ‘will be isothermal lines. If we divide the globe 
into ints of longitude, and compare the iraerical proportions of those 
lines under similar isothermal latitudes, the e a ce of different aha 
of grouping will at once be evident. From such systems can be distin- 
-peggk even in the present imperfect state of 6 our ee those of the 
new world, of Western Africa, of India, and of New Hol land. As we 
that; dalirithatanding the regular increase of heat from the equator to the’ 
poles, the maximum of heat is not always identical in different countries, 
in different degrees of longitude ; so there exists places where certain fam- 
ilies attain a greater degree of development than elsewhere ; as is the case 
with Composite in the temperate region of North America, and especially 
at the southern extremity of Africa.” 
Now follow tables of the different numerical proportions of certain exten- 
ty families and se er of plants, as far as they have been ascertained. 
I give them in Humboldt’s words, with a few interpolations, which are dis- 
tinguished by being included within crotchets [ } 
* ACOTYLEDONES. 
4 for the mountains. In the Fak zone cry ae 90 are gen- 
are 58 crypt. t to 67 phenog., o see equi ial: in Sw sea according to the 
computation of, Wahlenberg, they are something less than 4 to 1; and it 
is probable that this is a near approximation to the true pro portions. 
Sweden, the cryptogamic flora of that country apd been more accurate- 
ly inv estigated than that of any other part of the 
“In separating cryptogamous plants into ince renal we Sharve that 
ferns are more numerous, the derominatot of the fraction being smaller in 
the frozen than in the temperate zone. L.ichens and mosses also pee ie» 
towards the frozen zone. The geo graphical distribution of ferns d 
apes! e combination of local cireumstances of shade, humidity, ad bane : 
warmth. ‘The maximum (that is to say, the place where the denom- — 
_imator sof the fraction of the group becomes the smallest pooeitle) is found ; 
i, 
w « 
