6f vegelalle Forms. 447 
barometrica! heights, ‘* because,”’ as he says, ** he has a great 
contempt for every result taken from barometrical measurement.” 
His Geography of the Plants in the South of France was followed 
by the Jentamen Historie geographice Vegetabilium of the 
learned Professer Strohmayer, published in 1800 at Gottingen 
in the form of a dissertation ; but thisTentamen exhibits rather 
the plan of a future work, and the catalogue of authors to be 
consulted, than information respecting the altitudes which spon- 
taneous plants reach in different climates. The case is the same 
with the very philosophical views announced by M. Treviranus 
in his Essai de Kiologie; we therein find general considerations, 
but no measurements of heights, and no thermometrical indica-~ 
tions, which are the solid bases of the geography of plants. This 
study has not risen to the rank of a scjence, until men of science 
have perfected both the measures of heights by baroimetrical 
observations, and the determination of mean temperatures ; or, 
what is more important fer the development of vegetation, the 
determination of the differences between the temperature of 
summer and winter and between that of day and night. Few 
branches of study have in our day made more rapid progress ; and 
a long time has not intervened between the first efforts and the 
present period, when by the united observations of a great num- 
ber of travellers, we have sueceeded in fixing the limits of ve- 
getables in Lapland, the Pyrenees, tlie Alps, Caucasus, and the 
Cordilleras of America. 
The vegetables which cover the vast surface of the globe pre- 
sent, when we study by natural classes or families, striking dif- 
ferences in the distribution of their forms: it is to the laws of this 
distribution that I have recently turned my attention. On li- 
miting them to the countries in which the number of the species 
is exactly known*, and by dividing this number by that of the 
Glumacece +, the leguminous plants, the labiated, and the com- 
pound, we find numerical relations which form very regular 
series. We see certain forms become more common from the 
¢quator towards the pole, like the ferns, the glumacez, the eri- 
cinee, and the rhododendrons. Other forms on the contrary in- 
erease from the poles towards the equator, and may be consi- 
dered in our hemisphere as southern forms: such are the ru- 
biacee, the malvacew, the euphorbia, the leguminous and the 
composite plants. Finally, others attain their maximum even 
ia the temperate zone, and diminish also towards the equator 
'* Lapland, France, England, &c. according to Messrs. Wahlenberg, 
Buch, Ramond, Decandolle, and Smith. 
+ The Glumacer contuiu the three families of Graminca, Cyperacee, and 
Juncacee. 
and 
