Affinis C. externa, Good., qua? perigyniis eostato-nervosis, glaucis, squamis masculis rnutieis, foliis, bracteisque patentibus vel recurvis, ssepe involutis, differt. Boott.
12. Caeex trifida, Cav., vicl. Fl. Antarct. Pt. 1. p. 89.
Hab. Cape Tres Montes, C. Darwin, Esq. ; Falkland Islands, abundant, I)' Urville, Capt. Sutivan, j. n. h.
A very noble species, abundant in the Falkland Islands, growing with, and emulating in size, young Tussock grass. Mr. Darwin alone has gathered it on the American continent, and he only at Cape Tres Montes. Its confined range is very singular, for it can scarcely have been overlooked in Fuegia or the Strait of Magalhaens, had it existed there ; and it is also probably the only plant common to New Zealand and the Falkland Islands, not found abundantly in Tierra del Fuego.
Carex trifida affords a remarkable instance of apparent caprice in its choice of habitat ; for though common in the Falklands, along with the Bacti/Us caspitosa (Tussock grass), and though there these grow in company, and under precisely the same conditions, yet the Tussock grass in America only appears in the southern extreme of Fuegia, where it is unaccompanied by Carex trifida ; whilst the latter is confined to a latitude eight hundred miles north of Cape Horn. There is nothing whatever in the climate or soil of any part of western South Chili, or Fuegia, that can be pronounced unfavoiuable to the growth of this Carex, whose absence there naturaUy leads to the question, how is its presence in Cape Tres Montes and the Falkland Islands to be accounted for ? did it originate in each of these two isolated localities ? was the seed transported over the intervening land, by an agent whose operations were limited to the eastern, and western extremes only of Antarctic America? or, have the individuals that once tenanted the intervening land, been destroyed ? Any one of these hypotheses is at first sight plausible, and the first, perhaps, the most so, New Zealand being a third, and far more remote, habitat for this same species, which may thus be supposed to have had three separate origins. Such a question should not be discussed with reference to a single species, but as one which concerns all organized nature, whose phenomena are amenable to general laws. Hypotheses, adopted to account for exceptional cases, if not viewed in reference to the general rule from which these exceptions deviate, are generally fallacious ; and however much so, they still are apt to be magnified into laws. If we knew only such plants as are sporadic (the term given to species which inhabit unconnected and remote localities) we might, perhaps, be justified in assuming it as an axiom, that individuals of a species have sprung, at isolated localities, from as many similar parents : the cases which appear to demand this solution are, however, exceptions in Botanical Geography.
The study of the distribution of any one species or genus, or of the Flora of any one country, does not afford scope enough for investigating satisfactorily such a subject as the origin of the individuals of plants. If species, genera, and small natural orders were sporadic, recurring wherever climate and soil presented similar conditions, several points of origin for the same species might be assumed. But it is not so: species, genera, and orders are distributed within geographical limits, according to their extent : the great mass of individual plants in the one case, and of forms in the other, appear to have sprung from single centres, in the former case from a common parent, and to have radiated from one point to greater or less distances around it, in proportion to the facilities for migration and absence of checks to diffusion. The explanation of exceptions to this prevailing rule must then be sought in some natural cause, capable of counteracting the general law, and not what, if adopted for the case of one species, must be conceded with respect to all, and consequently force us to conclude that two classes of agents are required to effect one object, namely, the dispersion of vegetables.
7. TJNCINIA, Pers.
1. Uncinia tenttis, Poepp., Sgnops. Plant. Am. Austr. vol. iii. n. 240. Kunze, Synops. der Reidgr. t. 21. Kunth, En. Plant, vol.ii. p. 525.
