50 Baron HumbolOt on the Lazve which are observed 
blished, which results from the necessity of food, and the habi- 
tudes of life.; but the causes which have limited the forms^ are 
hidden under the impenetrable veil which conceals from our 
sight all that extends from the origin of things to the first de- 
velopment of organic hfe. 
On examining in detail all that we already know regarding 
the proportion of monocotyledonous to dicotyledonous plants, 
we find that the denominator becomes gradually smaller (and 
this with a very great degree of regularity), in proceeding from 
the equator toward the 62d degree of N. Lat. It increases 
probably anew in regions still more northern, on the coast of 
Greenland,. where the Gramineae have become very rare {CongOy 
p. 4.). The proportion varies from to ^ in the different parts 
of the tropics. In upwards of 3880 phaenogamous plants of 
Equinoctial America, found by M. Bonpland and myself in 
flower and in fruit, there were 654 monocotyledones, and 3226 
dicotyledones: hence the great division of monocotyledones would 
be I of the phaenogamous plants. According to Mr Brown, the 
proportion is generally in the Old Continent (in India, Equi- 
noctial Africa, and New Holland,) 
In the temperate zone, we find (according to my Proleg. p. xii. 
and the partial results published by M. Decandolle, Diet, des 
Sciences Nat vol. xviii. p. 594,-597.) that the monocotyledones 
are to the dicotyledones. 
In Barbary, 
-. 1 : 4,8 
In France, - - - 
= 1 . 4,7 
Egypt, 
o 
li 
Germany, 
- 1 : 4,0 
Caucasus and Crimea, 
11 
05 
o 
Switzerland, 
1 : 4,3 
Kingdom of Naples, 
1! 
The British Isles, 
= 1 : 3,6 
The State of Venice, 
11 
o 
North America, 
1! 
In the frigid zone, the proportion is, 
In Lapland, - - 1 : 2,8 
Iceland, - - = 1 : 2,8 
We see, that, from the tropics to the pole, the relative increase 
of the monocotyledones is very regular. As the monocotyledones 
affect moisture, they are more numerous in the British Isles, 
and more rare in Egypt and on the dry mountains of Caucasus. 
I have already observed, that in the Alps of Switzerland, up to 
the region of the Rhododendra, the monocotyledones are to the 
