VI FLOKA OF TASMANIA. 
companied with a greater tendency to permanence in form : thus Aeotyledons, Monocotyledons, and 
Dicotyledons are an ascending series in complexity and in constancy of form. In Dicotyledons, 
Salices, Urticea, Chenopodiacea, and other Orders with incomplete or absent floral envelopes, vary 
on the whole more than Leguminosce, Lythracece, Myrtacece, or Rosacea, yet members of these pre- 
sent, in all countries, groups of notoriously varying species, as Eucalyptus in Australia, Rosa in Europe, 
and Lotus, Epilobium, and Rubus in both Europe and Australia. Again, even genera are divided : of 
the last named, most or all of the species are variable j of others, as Epacris, Acacia, and the majority 
of such as contain upwards of six or eight species, a larger or smaller proportion only are variable. 
But the prominent fact is, that this element of mutability pervades the whole Vegetable Kingdom ; 
no class nor order nor genus of more than a few species claims absolute exemption, whilst the grand 
total of unstable forms generally assumed to be species probably exceeds that of the stable. 
5. The above remarks are equally applicable to all the higher divisions of plants. Some 
genera and orders are as natural, and as limitable by characters, as are some species ; others 
again, though they contain many very well-marked subordinate plans of construction, yet are so 
connected by intermediate forms with otherwise very different genera or orders, that it is im- 
possible to limit them naturally. And as some of the best marked and limited species consist of 
a series of badly marked and illimitable varieties, so some of the most natural* and limitable orders 
and genera may respectively consist of only nndefinable groups of genera or of species. For instance, 
both Graminece and Composite are, in the present state of our knowledge, absolutely limited Orders, 
and extremely natural ones also j but their genera are to a very eminent degree arbitrarily limited, 
and their species extremely variable. Orchidecs and Leguminosce are also well-limited Orders (though 
small genera and the fact that monotypic genera seldom have their variations recorded in systematic works, but an 
examination of his data and methods compels me to acquiesce in his statement. It has also been remarked (Bory de 
Saint-Vincent, Toy. aux Quatre lies de l'Afrique) that the species of islands are more variable than those of continents, 
an opinion I can scarcely subscribe to, and opposed to Mr. Darwin's facts, inasmuch as insular Floras are characterized 
by peculiar genera, and by having few species in proportion to genera. Bisexual trees and shrubs are generally 
more variable than unisexual, which however is only a corollary from what is stated above regarding plants of simple 
structure of flower. On the whole, I think herbs are more variable than shrubby plants, and annuals than perennials. 
It would be curious to ascertain the relative variableness of social and scattered plants. The individuals of a social 
plant, in each area it is social upon, are generally very constant, hut individuals from different areas often differ much. 
The Pinus sglvestrls, Mughis, and uncinate are cases in point, if considered as varieties of one ; as are the Cedars of 
Atlas, Algeria, and the Himalaya. 
* It should be borne in mind that the term natural, as applied to Orders or other groups, has often a double 
significance ; every natural order is so in the sense of each of its members being more closely related to one or more 
of its own group than to any of another ; but the term is often used to designate an easily limited natural order, that 
is, one whose members are so very closely related to each other by conspicuous peculiarities that its differential cha- 
racters can be expressed, and itself always recognized ; these may be called objective Orders ; Orchidece and Graminece 
are examples. Any naturalist, endowed with fair powers of observation and generalization, recognizes the close affi- 
nity between a pseudobulbous epiphytical, and a terrestrial tuberous-rooted Orchid, or between the Bamboo and 
Wheat, though the differences are exceedingly great in habit and in organs of vegetation and reproduction. Other 
orders are as natural and may be as well hmited, but having no conspicuous characters in common, and presenting 
many subordinate distinct plans of structure, may be regarded as subjective. Such are Ranunculacece and legu- 
minous, of which a botanist must have a special and extensive knowledge before he can readily recognize very many 
of their members. No degree of i able an uninstructed person to recognize the close affinity o f 
Clematis and Ranunculus, or of Acacia and Cytisus, though these are really as closely related as the Orchids and 
e. We do not know why some Orders are subjective and some objective ; but if the theory 
is a true one, we ought through it to reach a solution. 
