O GENERAL REMARKS ON THE 



According to the numbers already stated the Dicotyledones 

 of Terra Australis are to be 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 extensive orders 

 of Monocotyledones, especially Gramiuese and Cyperaceae, 

 are considerably nnder-rated ; an addition of 500 species 

 to Monocotyledones 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 catalogues or Floras which appeared 

 most to be depended on, and have likewise had recourse to 

 unpublished materials of great importance in ascertaining 

 this point. The general results of this examination are, 

 that from the equator to 30° of latitude, in the northern 

 hemisphere at least, the species of Dicotyledonous plants 

 are to Monocotyledones as about 5 to 1 ; in some cases con- 

 siderably exceeding, and in a very few falling somewhat 

 short of this proportion ; and that in the higher latitudes a 

 538] gradual diminution of Dicotyledones takes place, until in 

 about 60° N. lat. and 55° S. lat. they scarcely equal half 

 their intratropical proportion. 



In conformity with these results the Dicotyledones should 

 be to the Monocotyledones of Terra Australis as nearly 9 

 to 2 ; whereas the actual proportion as deduced from our 

 materials is hardly 7 to 2 : but it appears, on arranging 

 these materials geographically, that the relative proportions 

 of the different regions of Terra Australis itself, are equally 

 at variance with these results. About half the species of 

 Australian plants at present known have been collected in 

 a parallel included between 33° and 35° S. lat. ; for this 

 reason, and for one which wdll hereafter appear, I shall call 

 this the principal parallel. At the eastern extremity of 

 this parallel, within the limits of the colony of Port Jack- 

 son, where our materials are the most perfect, the propor- 



