Page:The Botany of the Antarctic Voyage.djvu/129

Campbell's Islands.] upper regions forming small tufts of the ordinary mode of growth in ferns. Besides these variations in size and luxuriance, depending wholly upon climate, I find that the pinna? and pinnules are more or less remote, with longer or shorter apices, and the segments of the latter are either decidedly rounded and blunt, or all acuminated and pungent ; in general, however, the lower segments are obtuse and the upper acute. As a species it is abundantly distinct from A. proliferum, Br., in the presence of the large palese. In New Zealand it is probably even a more sportive plant than iu the islands now under consideration, for I am inclined to refer to it Mr. Colenso's A. TFaikareme, A. sylvaticiim, and A. pulcherrimum.

The islands of New Zealand have long been known to produce a very large proportion of Ferns compared to their phaenogamic plants ; a circumstance which must strike the most casual observer. Being an attractive branch of Botany, it might be supposed that the excess of this Natural Order was rather apparent than real, and only due to its species being more generally collected and transmitted to England : but this is not wholly the case, the exertions of recent collectors having increased this proportion, to what is probably the maximum; for being more widely distributed than the higher orders, the hitherto partially explored middle island may be expected to produce new forms of flowering plants, accompanied with a large number of Ferns it is true, but those of species already detected elsewhere. The species of widely spread natural orders, being very frequently themselves distributed over large areas, it follows that the relative amount which such bear to the remainder of the vegetable kingdom, in a country so large as New Zealand, cannot be ascertained from an examination of the productions of one half of its area only. Mr. Brown has stated (Expedition to Congo, App. p. 462) the conditions which appear most requisite for the abundant production of Ferns, and these are to a great extent amply fulfilled in the position and climate of New Zealand ; for not only the number of species is great, but the mode of growth of many is indicative of a lower latitude than they inhabit, no less than six assuming the arborescent form, one of which attains the 47 th degree of south latitude : besides this, other species, whose stipites spring from the root at once, become caulescent, having their fronds disposed on the apex of the caudex, as those of the true tree-ferns are, giving a totally different, as well as far more beautiful habit to the plant. Of this there are a few examples in New Zealand, as the Aspidium pennigeriim and several species of Lomaria, and a more striking one in the Asp. venustum, which presents this unexpected appearance in the high latitude (for these regions) of the 53rd degree, and is wholly due to the shade, moisture, and equable climate of the sea-level in Lord Auckland's group and Campbell's Island ; for on ascending the hills, or even leaving the woods, this fern assumes the ordinary appearance of other Aspidia.

Although the most abundant production of Ferns is found under the physical features of shade, moisture, and a certain amount of heat, these are not on the one hand always present where the Ferns do preponderate to a great degree, nor on the other do the latter always appear where these conditions are the most evident.

The small island of St. Helena has its Flora composed of nearly equal portions of Pluenogamic plants, Ferns, and other Cryptogamiae, the Ferns forming about a third part of the whole, and nearly equalling the flowering plants ; this is only to be expected from St. Helena fulfilling the above conditions in a most eminent degree. The little island of Ascension, on the other hand, about 500 miles distant, is proverbially called a cinder, with hardly water sufficient to supply a garrison composed of a mere handful of men, and absolutely but one small drip, rather than spring, in the whole island, supplied by the percolation of condensed sea-vapours on the narrow top of a hill, 2818 feet high; no shade exists any where, and the soil is porous volcanic scoria?, that scorches the feet after being heated by a tropical sun ; under all these circumstances it produces likewise as many Ferns as native flowering plants. It is true that they are confined to the top of Green Mountain, whose slopes in many places are completely covered by them, but they enjoy no shade, the only native woody plant not attaining two feet in height ; and what is more remarkable, out of nine species of Ferns existing under these circumstances, only two are common to Ascension Island and St. Helena ; several are peculiar to their isolated position, and one is a species of Mara/da, a genus I believe to be in general particularly impatient of exposure. I kuow no parallel instance to this amongst the Atlantic islands ; a far larger proportion of the ferns, both of St. Helena and of Tristan d'Acunha, is common to both these spots, and to other parts of the globe, than are those of Ascension ;