APPENDIX, 
537 
Primary Classes .] 
tribes of plants they are necessarily arranged according to the natural 
method. 
Of this method the primary classes are Dicotyledones, Monocoty- 
ledones, and AcotylEdones. 
These three divisions may be admitted as truly natural, and their 
names, though liable to some exceptions, appear to me the least objection- 
able of any hitherto proposed. 
Of the Australian plants at present known, upwards of 2900 are Dico- 
tyledonous ; 860 Monocotyledonous ; and 400 Acotyledonous, Ferns being 
considered as such. 
It is well known that Dicotyledonous plants greatly exceed Monoco- 
tyledonous in number ; I am not however aware that the relative propor- 
tions of these two primary divisions have any where been given, or that 
it has been enquired how far they depend on climate. Into this subject I 
can enter only very generally in the present essay. According to the 
numbers already stated the Dicotyledones of Terra Australis are to the 
Monocotyledones as rather more than 3 to 1, or somewhat less than 
7 to 2. 
In Persoon’s Synopsis, to which, as the latest general work, I again 
refer, these two classes are to each other nearly as 11 to 2. But, from the 
nature of this compilation, it may be assumed that certain difficult and ex- 
tensive orders of Monocotyledones, especially Gramineae and Cyperaceae, 
are considerably under-rated ; an addition of 500 species to Monocotyle- 
dones would make the relative numbers of the two classes as 9 to 2, which 
I am inclined to think an approximation to the true proportion. 
With a view to determine how far the relative proportions of these 
two classes are influenced by climate, I have examined all the local cata- 
logues or Floras which appeared most to be depended on, and have like- 
wise had recourse to unpublished materials of great importance in ascer- 
taining this point. The general results of this examination are, that from 
the equator to 30° of latitude, in the northern hemisphere at least, the spe- 
cies of Dicotyledonous plants are to Monocotyledones as about 5 to 1; in 
some cases considerably exceeding, and in a very few falling somewhat 
short of this proportion ; and that in the higher latitudes a gradual dimi- 
3 Z 
VOL. II. 
