account; for at the southern extremity of Van Diemen's Island, where the necessary conditions exist, the relative proportion of Cryptogamous plants is not materially different from that of the south of Europe.
In that which I have called the principal parallel of New Holland, however, Cryptogamous plants appear to be much less numerous than in the corresponding latitudes of the northern hemisphere; and within the tropic they probably do not form more than one twelfth of the whole number of species.
In several of the islands of the Gulf of Carpentaria, having a Flora of Phænogamous plants exceeding 200 species, I did not observe a single species of Moss.
From the three primary classes of plants already treated of I proceed at once to those groups called Natural Orders or Families; for the intermediate divisions are too much at variance with the natural series to be made the subject of such general remarks as have been already offered on the primary classes, and which are equally admissible with respect to the natural families.
A methodical, and at the same time a natural, arrangement of these families is, in the existing state of our knowledge, perhaps impracticable. It would probably facilitate its future attainment, if at present, entirely neglecting it, attention were turned to the combination of these orders into Classes equally natural, and which, on a thorough investigation, might equally admit of being defined. The existence of certain natural classes is already acknowledged, and I have, in treating of the Australian natural families, ventured to propose a few that are perhaps less obvious, still more, however, might have been suggested had this been the place for pursuing the subject.
540] The natural orders in the Genera Plantarum of Jussieu are exactly 100; subsequent observations of Jussieu himself and of other botanists have considerably increased their numbers, so that in the lately published Théorie Elémentaire de la Botanique of Decandolle they amount to 145.
The plants of Terra Australis are referable to 120
