As some of the Bambusaceæ (arborescent grasses) advance into the temperate zone, so within the tropics they do not suffer from the temperate climate of the mountains. They certainly grow more luxuriantly as social plants from the sea coast to the height of about 2560 English feet; for example, in the province de las Esmeraldas, west of the Volcano of Pichincha, where Guadua angustifolia (Bambusa Guadua in our Plantes équinoxiales, T. i. Tab. xx.) produces in its interior much of the siliceous Tabaschir (Sanscrit tvakkschira, ox-milk). In the pass of Quindiu we saw the Guadua growing at an elevation which we found by barometric measurement to be 5400 (5755 English) feet above the level of the Pacific. Nastus borbonicus is called by Bory de St. Vincent a true Alpine plant; he states that it does not descend lower on the declivity of the Volcano in the Island of Bourbon than 3600 (3837 English) feet. This recurrence or repetition as it were at great elevations of the forms characteristic of the hot plains, recalls the mountain group of palms before pointed out by me (Kunthia Montana, Ceroxylon andicola, and Oreodoxa frigida), and a grove or thicket of Musaceæ sixteen English feet high (Heliconia, perhaps Maranta), which I found growing isolated at an elevation of 6600 (7034 English) feet, on the Silla de Caraccas. (Rélation hist. T. i. p. 605-606.) As, with the exception of a few isolated herbaceous dicotyledones, grasses form the highest zone of phænogamous vegetation round the snowy summits of lofty mountains, so also, in advancing in a horizontal direction towards either pole of the Earth, the phænogamous vegetation terminates with grasses.
To my young friend Joseph Hooker, who, but just returned with Sir James Ross from the frozen antarctic regions, is now exploring the Thibetian portion of the Himalaya, the geography of plants is indebted not only for a great mass of important materials, but also for excellent general deductions. He calls attention to the circumstance that phænogamous flowering plants (grasses) approach 17½° nearer to the Northern than to the Southern pole. In the Falkland Islands near the thick masses of Tussack grass (Dactylis cæspitosa, Forster, according to Kunth a Festuca), and in Tierra del Fuego or Fuegia, under the shade of the birch-leaved Fagus antarctica, there grows the same Trisetum subspicatum which extends over the whole range of the Peruvian Cordilleras, and over the Rocky Mountains to Melville Island, Greenland, and Iceland, and which is also found in the Swiss and Tyrolese Alps, in the Altai mountains, in Kamtschatka, and in Campbell Island, south of New Zealand; therefore, from 54° South to 74½° North latitude, or through 128½° of latitude. “Few grasses,” says Joseph Hooker, in his Flora Antarctica, p. 97, “have so wide a range as Trisetum subspicatum, (Beauv.) nor am I acquainted with any other Arctic species which is equally an inhabitant of the opposite polar regions.” The South Shetland Islands, which are divided by Bransfield Strait from D’Urville’s Terre de Louis Philippe and the Volcano of Haddington Peak, situated in 64° 12´ South latitude and 7046 English feet high, have been very recently visited by a Botanist from the United States of North America, Dr. Eights. He found there (probably in 62° or 62¼°, S. latitude) a small grass, Aira antarctica (Hooker, Icon. Plant. Vol. ii. Tab. 150) which is “the most antarctic flowering plant hitherto discovered.”
In Deception Island, of the same group, S. lat. 62° 50´, lichens only are found, and not a single species of grass; and so also farther to the south-east, in Cockburn Island (lat. 64° 12´), near Palmer’s Land, there were only found Lecanoras, Lecideas, and five Mosses, among which was our German Bryum argenteum: “this seems to be the ultima Thule of antarctic vegetation.” Farther to the south, land-cryptogamic, as well as phænogamic, vegetation is entirely wanting. In the great bay formed by Victoria Land, on a small island which lies opposite to Mount Herschel (S. lat. 71° 49´), and in Franklin Island, 92 geographical miles North of the great volcano Mount Erebus, 12400 English feet high (latitude 76° 7´ South), Hooker found not a single trace of vegetable life. It is quite different in respect to the extension even of the forms of higher vegetable organisation in the high northern latitudes. Phænogamous plants there approach 18½° nearer to the pole than in the southern hemisphere: Walden Island (N. lat. 80½°) has still ten species. The antarctic phænogamous vegetation is also poorer in species at corresponding distances from the pole (Iceland has five times as many flowering plants as the southern group of Auckland and Campbell Islands), but this less varied antarctic vegetation is from climatic reasons more luxuriant and succulent. (Compare Hooker, Flora antarctica, p. vii., 74, and 215, with Sir James Ross, Voyage in the Southern and Antarctic Regions, 1839-1843, Vol. ii. p. 335-342.)
[28] p. 28.—“Ferns.”
If, with a naturalist deeply versed in the knowledge of the Agamæ, Dr. Klotzsch, we estimate the whole number of cryptogamic species hitherto described at 19000, this gives to Fungi 8000 (of which the Agarici constitute 1-8th); Lichens, according to J. von Flotow of Hirschberg, and Hampe of Blankenburg, at least 1400; Algæ 2580; Mosses and Liver-worts, according to Carl Müller of Halle, and Dr. Gottsche of Hamburgh, 3800; and Ferns 3250. We are indebted for this last important result to the thorough investigation of all that is known concerning this group of plants by Professor Kunze of Leipsic. It is remarkable that of the entire number of described Filices the family of Polypodiaceæ, alone, comprises 2165 species; while other forms, even Lycopodiaceæ and Hymenophyllaceæ, only count 350 and 200. There are, therefore, almost as many described ferns as described grasses.
It is remarkable that in the ancient classic writers, Theophrastus, Dioscorides, and Pliny, no notice occurs of the beautiful form of arborescent ferns; while from information derived from the companions of Alexander, Aristobulus, Megasthenes, and Nearchus, mention is made of Bamboos “quæ fissis internodiis lembi vice vectitabant navigantes;” of the Indian trees “quarum folia non minora clypeo sunt;” of the fig-tree of which the branches take root round the parent stem; and of Palms “tantæ proceritatis, ut sagittis superjici nequeant.” (Humboldt, de Distributione geogr. Plantarum, p. 178 and 213.) I find the first description of tree-ferns in Oviedo’s Historia de las Indias, 1535, fol. xc. This experienced traveller, who had been placed by Ferdinand the Catholic as director of the gold-washings in Hayti, says: “Among the many ferns there are some which I reckon among trees, for they are as thick and as tall as pines (Helechos que yo cuento por arboles, tan gruesos como grandes pinos y muy altos). They grow chiefly in the mountains and where there is much water.” The height is exaggerated. In the dense forests round Caripe even our Cyathea speciosa only attains a height of 30 to 35 (32 to 37 English) feet; and an excellent observer, Ernst Dieffenbach, in the northernmost of the three islands of New Zealand saw no stems of Cyathea dealbata of more than 40 (42½ English) feet in height. In the Cyathea speciosa and the Meniscium of the Chaymas missions we observed, in the midst of the shadiest primeval forest, in very luxuriantly growing individuals, the scaly stems covered with a shining carbonaceous powder. It seemed like a singular decomposition of the fibrous parts of the old frond stalks. (Humboldt, Rel. hist. T. i. p. 437.)
Between the tropics, where, on the declivities of the Cordilleras, climates are placed successively in stages one above another, the proper zone of the tree-ferns is between three and five thousand feet (about 3200 and 5330 English) above the level of the sea. In South America and in the Mexican highlands they seldom descend lower towards the plains than 1200 (about 1280 Eng.) feet. The mean temperature of this happy zone falls between 17° and 14°.5 Reaumur (70°.2 and 64°.6 Fahr.) This region enters the lowest stratum of clouds, or that which floats next above the sea and the plains; and hence, besides great equality of temperature, it also enjoys uninterruptedly a high degree of humidity. (Robert Brown, in Appendix to Expedition to Congo, p. 423.) The inhabitants, who are of Spanish descent, call this zone “tierra templada de los helechos.” The Arabic word for fern is feledschun, f being changed into h in helechos according to Spanish custom: perhaps the Arabic feledschun is connected with “faladscha,” “it divides;” in allusion to the finely divided margins of fern leaves or fronds. (Abu Zacaria Ebn el Awam, Libro de Agricultura, traducido por J. A. Banqueri, T. ii. Madr. 1802, p. 736.)
The conditions of mild temperature and an atmosphere nearly saturated with vapour, together with great equability of climate in respect to both temperature and moisture, are fulfilled on the declivities of the mountains, in the valleys of the Andes, and above all in the mild and humid atmosphere of the southern hemisphere, where arborescent ferns extend not only to New Zealand and Van Diemen Island (Tasmania), but even to the Straits of Magellan and to Campbell Islands, or to a latitude almost corresponding to that of Berlin in the northern hemisphere. Of tree-ferns, Dicksonia squarrosa grows vigorously in 46° South latitude, in Dusky Bay (New Zealand); D. antarctica of Labillardière in Tasmania; a Thyrsopteris in Juan Fernandez; an undescribed Dicksonia with stems from 12 to 15 (nearly 13 to 16 English) feet in the south of Chili, not far from Valdivia; and a Lomaria of rather less height in the Straits of Magellan. Campbell Island is still nearer to the south pole, in 52½° lat., and even there the stem of the Aspidium venustum rises to 4 feet (4 feet 3 inches, English) before the fronds branch off.
The climatic relations under which Ferns in general flourish, are manifested in the numerical laws of their quotients of distribution taken in the manner alluded to in an earlier part of the present volume. In the low plains of the great continents within the tropics, the quotient for ferns is, according to Robert Brown, and according to late researches, 1-20th of all the species of phænogamous plants growing in the same region; in the mountainous parts of the great continents in the same latitudes it is from 1-8th to 1-6th. But a very different ratio is found in the small islands dispersed over the wide ocean. The proportion of ferns to the whole number of Phanerogamæ increases there in such a manner that in the groups of islands between the tropics in the Pacific the ferns equal a fourth,—and in the solitary far detached islands in the Atlantic Ocean, St. Helena, and Ascension,—almost equal the half of the entire phænogamous vegetation. (See an excellent memoir of D’Urville entitled Distribution géographique des Fougères sur la surface du Globe, in the Annales des Sciences Nat. T. vi. 1825, p. 51, 66, and 73). From the tropics (where in the great continents D’Urville estimates the ratio generally at 1:20) we see the relative frequency of ferns decrease rapidly in the temperate zone. The quotients are: for North America and for the British Islands 1⁄33, for France 1⁄58, for Germany 1⁄52, for the dry parts of the south of Italy 1⁄74, and for Greece 1⁄84. Towards the colder regions of the north we see the relative frequency increase again rapidly; that is to say, the number of species of ferns decreases much more slowly than does the number of species of phænogamous plants. At the same time, the luxuriance, abundance, and mass of individuals in each species augments the illusive impression of absolute numbers. According to Wahlenberg’s and Hornemann’s Catalogues the relative numbers of Filices are, for Lapland 1⁄25, for Iceland 1⁄18, and for Greenland 1⁄12.
Such, according to the present state of our knowledge, are the natural laws manifested in the distribution of the pleasing form of Ferns. But it would seem as if in the family of Ferns, which has so long been regarded as a cryptogamic family, we had quite recently arrived on the traces of another natural law, a morphological one of propagation. Count Leszczyc-Suminski, who happily unites the gift of microscopic examination with distinguished artistic talent, has discovered in the prothallium of ferns an organisation by which fructification is effected. He distinguishes a bisexual arrangement in the ovule-like cell on the middle of the theca, and in the ciliated antheridia or spiral threads before examined by Nägeli. The fertilisation is supposed to take place not by pollen tubes but by the moveable ciliated spiral threads. (Suminski zur Entwickelungs-geschichte der Farrnkräuter, 1848, S. 10-14.) According to this view, Ferns, as Ehrenberg expresses it (Monatl. Berichte der Akad. zu Berlin, Januar 1848, S. 20), would be produced by a microscopic fertilisation taking place on the prothallium as a receptacle; and throughout the whole remainder of their often arborescent development they would be flowerless and fruitless plants, forming buds or bulbs; the spores or sori on the under side of the frond not being seeds but flower buds.