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4. Die Geographie der Farne.
This work, from the hand of a most eminent pte [ unclear: ] ndologist, is obviously of special interest to New Zealand biologists. It is divided into a general introduction and two parts, the first (pp. 9–136) being ecological, and the second (pp. 139–333) floristic. There is also a bibliography, which does not aim at completeness, of 182 titles arranged according to the various fern floras and their divisions, together with those dealing with general plant-geography, general works on ferns, and studies on special ferns and groups. The illustrations show both individual plants and fern-associations. Fig. 124, entitled Leptopteris superba, taken by Cockayne, is really Polystichum vestitum, and the locality is not Stewart Island, but forest at base of Big Ben, Canterbury.
In the introduction it is pointed out that the general impression that ferns, through ease of distribution by their spores, are more readily spread than flowering-plants, and have a wider distribution, is not the case. Thirty years' study of fern material from all over the globe has convinced the author that, in general, the distribution of ferns goes parallel with that of phanerogams Where endemism is strong for the latter, so too is it with the accompanying ferns.
The ecological section is brimful of interest for New Zealand botanists, and requires close attention; a brief summary would be of no value. Many New Zealand species and genera are mentioned, while the ferns of other regions frequently exhibit parallel structure. Ferns, as a whole, are considered mesothermous hygrophytes and xerophytes.
Part II, dealing with fern floras, concerns students of bio-geography in general Certain fundamental principles and matters are first explained—e.g., endemism, which may be recent or ancient, as in the case of the New Zealand Loxsoma, with its sole relatives two species of Loxsomopsis of Central and South America; numerical relation of ferns to seed-plants in the different floral regions, and amongst other details it is shown that out of the 149 genera of ferns only thirty-three do not occur in the tropical forest-region, and of these Doodia, Loxsoma, Leptopteris, and Todea are confined to the South Temperate Zone; the fern-areas, which are, on the whole, more extensive than those of phanerogams, but yet a similar local endemism occurs in both classes; the cosmopolitan ferns, of which there are twelve well-defined (though it may be polymorphic) species, which occur with a few trifling exceptions over the whole globe*; pantropic ferns; the northern circumpolar extension of ferns, the author being of opinion that a backward current of species is moving northwards from a Tertiary haven of refuge for the forest-ferns in South China, the basal Himalayas, and Mexico; the arctic-alpine element, together with relics from the glacial period, but these are much fewer than are the flowering-plants of that character; and, finally, discontinuous areas of distribution, of which the following examples concern New Zealand: Blechnum Fraseri (New Zealand and Philippines), B. Patersoni, Gleichenia dicarpa, and other ferns of the Australasian flora, which, in common with the phanerogams, Spinifex, Melaleuca, and Casuarina, extend to the mountains or the strand of Malaya, and Todea barbara of New Zealand, Australia, and South Africa.
The distribution of certain genera is considered in detail: that of Ophioglossum, Botrychium, and Gleichenia alone concerns New Zealand. The forms of Ophioglossum are ill equipped for wide distribution, since they spread rather by a feeble vegetative increase than by their scanty spores. Their universal but quite local occurrence—for they are frequently isolated by wide tracts—together with their small amount of variation, is, according to the author, the greatest puzzle in the geography of ferns. In the far south of Australia and New Zealand, and in Argentina, South Chile, and Patagonia, the little northern species Botrychium lunaria occurs—an arctic footstep in the subantarctic! Between Ophioglossum and Botrychium a fundamental distinction exists, the former being tropical-cosmopolitan,
[Footnote] * The following are absent in [ unclear: ] New Zealand Adiantum capillus vener [ unclear: ] is, Pteris [ unclear: ] c etica Dryopter [ unclear: ] is [ unclear: ] s. Os [ unclear: ] munla regalis.
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but also mesothermous, and the latter horeal, but endowed with a strong power of expansion. Gleichenia is abundant in Tertiary rocks of Europe in its subgenera Mertensia and Euqleichenia, but the ice age drove it far to the south. The retreat of a Tertiary genus into the far oceanic south, with its insular climate, and into the tropical mountains, is most remarkable.
The author divides the earth, so far as ferns are concerned, into twelve floral regions, of which the Australia - New Zealand is one. The latter includes the rain-forest region of eastern Australia, Tasmania, and New Zealand. Central Australia is of no moment for ferns, and northern Australia comes into the Malayan region The boundary between the two fern floras extends from King Sound along the north coast to the east coast, and thence through Queensland to the tropic of Capricorn, beyond which, southwards, the Malayan element gradually fades away.
As for New Zealand, to quote the author's words, “The fern-world is not only one of the most luxuriant and largest, but floristically one of the most interesting. It is a little world of ferns in itself, where almost all the genera of tropical and temperate ferns are to be found.” A brief review of the species and genera is given, and their most important growth-forms; the presence of an endemic species of the tropical genus Lygodium is considered very remarkable. The author concludes: “It would be profitable to stay longer with this magnificent flora, which, though it is not the expression of a maximum hygrothermous forest climate, is easily the ideal fern climate of the present day, and plainly shows the optimum average conditions for the well-being of ferns.”
The interesting question of the circumpolar extension of the Australian-New Zealand fern flora is discussed. The special group which may, in a certain sense, be called “antarctic” is not at all of a boreal-arctic character, but rather of a temperate to a subtropical character. Neither are the species analogous with either arctic phanerogams or even antarctic with the highly characteristic cushion form of these latter. First come six species of Blechnum, two of Polystichum, two of Polypodium, Hymenophyllum ferrugineum, Asplenium obtusatum., and Schizaea fistulosa Also Todaea comes here, with its distribution in Australia, New Zealand, and South Africa. All the above are common to Australia - New Zealand, South America with Juan Fernandez, and in part South Africa. Hypolepis rugulosa may be also included (New Zealand, Reunion, Tristan d'Acunha, St. Helena, Juan Fernandez). The genus Dicksonia in closely related species extends from the Australasian floral region to oceanic Malaya, Juan Fernandez, and St. Helena. Then there is Schizaea, the most scattered, however, of all these genera.
The distribution of the above species may be explained on the supposition of a Tertiary or yet older region lying in the far south, whence they, in common with so many flowering-plants of the same area, extended radially. That the region in question was both ancient and warm is proved by the frondose structure and stems of the larger and the delicacy of the smaller ferns, Schizaca of Juncus form excepted. This element is a relic of a more extensive southern flora which dates from the Tertiary, or earlier, and which now remains on its small New Zealand-Australian area, thanks to the cinnatic conditions persisting that it requires. Further, in discussing the origin of the antarctic element of the south Chilian flora the author brings more facts in favour of an antarctic Tertiary centre of distribution, which is supported, moreover, by the additional fact of the presence of several Tertiary fossil ferns from Seymour Island which are related to, if not identical in some cases with, South American species.
L. C.