The Arabic designation for ferns is feledschun, filix, (from which the f has been changed, according to Spanish usage, into h,) and perhaps the term may be connected with the verb faladscha, “it divides,” from the finely cut margin of the frond.[[QQ]]
The conditions of genial mildness in an atmosphere charged with aqueous vapour and of great uniformity in respect to moisture and warmth, are fulfilled on the declivities of the mountains in the valleys of the Andes, and more especially in the southern milder and more humid hemisphere, where arborescent ferns advance not only to New Zealand and Van Diemen’s Land (Tasmania), but even as far as the Straits of Magellan and Campbell Island, and therefore to a southern latitude almost identical in degrees with the parallel in which Berlin is situated north of the equator. From among the family of arborescent ferns there flourishes the vigorous Dicksonia squarrosa, in 46° south lat. in Dusky Bay, New Zealand; D. antarctica of Labillardière in Tasmania; a Thyrsopteris in the Island of Juan Fernandez; an undescribed Dicksonia, whose stem is from 12 to 16 feet high, near Valdivia in Southern Chili; and a Lomaria, somewhat less in height, in the Straits of Magellan. Campbell Island is still nearer to the south pole, in 52½° lat., but even there the leafless stem of the Aspidium venustum rises to a height of more than four feet.
The climatic relations under which Ferns (Filices) in general flourish, are manifested in the numerical laws of their quotients of distribution. In the plains within the tropical regions of large continents this quotient is, according to Robert Brown, and from more recent investigations on the subject, ¹⁄₂₀ of all the phanerogamia, and in mountainous districts of large continents ⅙ to ⅛. This ratio is quite different on the small islands scattered over the ocean; for here the proportion borne by the number of ferns to the sum total of all the phanerogamic plants increases so considerably, that in the South-Sea Islands the quotient rises to ¼, while in the sporadic islands, St. Helena and Ascension, the number of ferns is almost equal to half of the whole phanerogamic vegetation.[[QR]] In receding from the tropics (where on the large continents d’Urville estimates the proportional number at ¹⁄₂₀), the relative frequency of ferns decreases rapidly as we advance into the temperate zone. The quotients are for North America and the British Islands ¹⁄₃₅, for France ¹⁄₅₈, for Germany ¹⁄₅₂, for the dry parts of Southern Italy ¹⁄₇₄, for Greece ¹⁄₈₄. The relative frequency again increases considerably towards the frigid north. Here the family of ferns decreases much slower in the number of its species than does that of phanerogamic plants. The luxuriantly aspiring character of the species, and the number of individuals contained in each, augment the deceptive impression of absolute frequency. According to Wahlemberg’s and Hornemann’s catalogues, the relative numbers of the Filices are for Lapland ¹⁄₂₅, for Iceland ¹⁄₁₈, for Greenland ¹⁄₁₂.
Such are, according to our present knowledge, the natural laws that manifest themselves in the distribution of the graceful form of Ferns. But it would seem as if in the family of Ferns, which have so long been regarded as cryptogamic, we had lately acquired evidence of the existence of another natural law,—the morphological law of propagation. Count Leszczyc-Suminski, who happily combines the power of microscopic investigation with a very remarkable artistic talent, has discovered an organisation capable of effecting fructification in the prothallium of ferns. He distinguishes two sexual apparatuses, of which the female portion is situated in hollow ovate cells in the middle of the sporangium, and the male in the ciliated antheridia, or the organs producing spiral threads, which have already been examined by Nägeli. Fructification is supposed to be effected by means of moveable ciliated spiral threads and not by pollen tubes.[[QS]] According to this view, Ferns would be, as Ehrenberg remarks,[[QT]] products of a microscopic fructification taking place on the prothallium, which here serves as a fertilizing receptacle, while throughout the whole course of their often arborescent development they would be flowerless and fruitless plants, having a bud-formation. The spores lying as sori on the under side of the frond are not seeds but flower-buds.
[99]. p. 229—“The Liliaceæ.”
Africa is the principal seat of this form; there the greatest diversity obtains; there they form masses and determine the natural character of the region. The New Continent exhibits also, it is true, magnificent Alströmeriæ and species of Pancratium, Hæmanthus, and Crinum. We have enriched the first of these genera with nine, and the second with three species; but these American liliaceous plants are more diffused and of less social habits than the European Irideæ.
[100]. p. 229—“The Willow Form.”
Nearly 150 different species of the main representatives of this form, or rather of the Willow itself, are already known. They cover the northern parts of the earth from the equator to Lapland. Their number and their varieties of form increase between the 46th and 70th degrees of latitude, more especially in that part of northern Europe which has been so remarkably indented by the early revolutions of our planet. I am acquainted with ten or twelve species of inter-tropical Willows, and these, like the Willows of the southern hemisphere, are deserving of special attention. As nature appears to delight in all zones in a wondrous multiplication of certain animal forms, as for instance, Anatidæ (Lamellirostres), and Pigeons; so likewise are Willows, Pines, and Oaks, widely diffused; the latter always exhibiting a similarity in their fruit, although various differences exist in the form of the leaves. In Willows belonging to the most widely different climates the similarity of the foliage, of the ramification, and of the whole physiognomical conformation, is almost greater than in Coniferæ. In the more southern part of the temperate zone, north of the equator, the number of the species of Willows decreases considerably; although (according to the “Flora atlantica” of Desfontaines) Tunis has still its own species, resembling Salix caprea; whilst Egypt, according to Forskäl, numbers five species, from the catkins of whose male blossoms is distilled the remedial agent Moie chalaf (aqua salicis), so much used in the East. The Willow which I saw in the Canaries is also, according to Leopold von Buch and Christian Smith, a peculiar species (S. canariensis), although common to those islands and to Madeira. Wallich’s catalogue of the plants of Nepaul and the Himalaya already gives 13 species belonging to the subtropical zone of the East Indies, and which have in part been described by Don, Roxburgh, and Lindley. Japan has its own species, of which one, S. japonica. (Thunb.), is also met with in Nepaul as an Alpine plant.
There was not, as far as I am aware, any species of Willow known as belonging to the tropical zone before my expedition, with the exception of S. tetrasperma. We collected seven new species, three of them on the plateaux of Mexico, at an elevation of 8500 feet above the level of the sea. Still higher, as for instance on the Alpine plains, between 12,000 and 15,000 feet, which we frequently visited, we saw nothing in the Andes of Mexico, Quito, and Peru, to remind us of the many small creeping Alpine Willows of the Pyrenees, the Alps, or of Lapland (S. herbacea, S. lanata, and S. reticulata). In Spitzbergen, whose meteorological relations have so much analogy with those of the snow-crowned summits of Switzerland and Scandinavia, Martius described two Dwarf-Willows, whose small woody stems and branches trail along the ground, and are so concealed in the turf-bogs that it is with difficulty their diminutive leaves can be discovered under the moss. The Willow species which I found in 4° 12′ south lat., at the entrance of the Cinchona or Peruvian Bark forests, near Loxa in Peru, and which has been described by Willdenow as Salix Humboldtiana, is most widely diffused over the western part of South America. A Beach-Willow (S. falcata), which we discovered on the sandy shores of the Pacific, near Truxillo, is, according to Kunth, probably a mere variety of the former. In like manner the beautiful and frequently pyramidal Willow, which we constantly saw on the banks of the Magdalena river, from Mahates to Bojorque, and which, according to the report of the natives, had only spread thus far within a few years, may also be identical with S. Humboldtiana. At the confluence of the Magdalena with the Rio Opon, we found all the islands covered with Willows, many of which had stems 64 feet high, with a diameter of from only 8 to 10 inches.[[QU]] Lindley has made us acquainted with a species of Salix belonging to Senegal, and therefore to the equinoctial region of Africa.[[QV]] Blume also found two species of Willow near the equator in Java, one wild and indigenous in the island (S. tetrasperma), and another cultivated (S. Sieboldiana). I am only acquainted with the two Willows belonging to the south temperate zone, which have been described by Thunberg (S. hirsuta and S. mucronata). They grow interspersed with Protea argentea, which has the same physiognomy as the Willow, and their leaves and young branches constitute the food of the hippopotamus of the Orange River. The family of Willows is entirely wanting in Australia and the neighbouring islands.
[101]. p. 229—“The Myrtle Form.”