448 On the Laws observed in the Distribution 
aud the poles. Such are the labiated plants, the amentacesx, 
the cruciferse, and the umbelliferee. Part of these data Jong since 
struck botanical travellers, and all those who have looked into 
herbals. It was known that the crucifere and umbellifere dis- 
appeared almost entirely in the plains of the torrid zone, and 
that none of the malvaceew were found beyond the polar circle. 
it is the same with the geography of the plants as with meteoro- 
logy. The results of those sciences are so simple that in all ages 
general ideas have been formed of them: but it is only after la- 
berious researches, and after having collected a great number of 
accurate observations, that numerical results were attained, and 
an acquaintance with the partial modifications undergone by the 
law of the distribution of forms. A table which we have drawn 
up exhibits this law with respect to sixteen families of plants 
distributed over the equatorial, temperate, and glacial zones. We 
there see with satisfaction mixed with surprise, how in organic 
nature, the forms present constant relations under the same zso- 
thermal parallels, 7. e. on curves traced by points of the globe 
which receive an equal quantity of heat. The grasses form in 
England 1-]2th, in France 1-13th, in North America 1-10th, 
of all the phanerogamous plants. The glumacee form in Ger- 
many 1-/th; in France 1-8th; in North America 1-8th; in 
New Holland, accor ding to the pecsanehes of Mr. Brown, 1- Sth ; 
of the known " phanerogamous plants. The composite plants in- 
crease a little in the northern part of the new continent ; for, 
according to the new Flora of Pursch, there is between the pa- 
rallels of Georgia and Boston 1-6th; whereas in Germany we 
find 1-Sth; and in France 1-7th, of the total number of the species 
with visible fructification. In the whole temperate zone, the 
glumacee and the composite plants form together, nearly one- 
fourth of the phanerogamous plants ; the glumacee, the com- 
posite, the crucifere and the leguminose, together nearly one- 
third. It results from these researches that the forms of or- 
ganized beings are in a mutual dependence, and that the unity 
of nature is such that the forms are limited, the one after the 
other, according to constant laws easy of determination. When 
we know upon any point of the globe the number of species pre- 
sented by one of the great families of the glumacee, the com- 
posite, the cruciferous, or the leguminous plants, we may estimate 
with considerable probability both the total number of the pha- 
nerogamous plants, and the number of species which compose 
the other vegetable families. It is thus that, by knowing under 
the temperate zone the number of the cyperacee or composite 
plants, we may guess at that of the gramineous or leguminous 
lants. 
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