OF all the spore-bearing families, the Ferns are the most universally known. They may easily be recognized by the coiling inwards of their young leaves in spring previous to expansion, and by the arrangement of the fruit on their undersides when expanded. The Ferns are exceedingly numerous both in genera and species, and vary from low herbaceous plants of an inch high, to trees with upright trunks forty or fifty feet or more in height, bearing a graceful coronet of leaves at their extremity. The tree ferns come to the utmost perfection in the warm, moist islands of the tropical oceans. Their boreal limit is about the thirty-seventh parallel of north latitude, but, on account of the vast extent of ocean in the southern hemisphere, they reach the fortieth or fiftieth parallel of south latitude, the more copious evaporation, and the consequently moister air and soil, being specially congenial to the fern tribe. For that reason a most luxuriant fern vegetation prevails in Juan Fernandez, Western Chili, and New Zealand. In the latter there are one hundred and twenty species, some of which are subarborescent, while others form tree ferns of considerable altitude. Shade is not absolutely requisite to ferns, for many of them grow luxuriantly when exposed to the sun, provided the soil be damp. The range of the non-arborescent ferns is very extensive. According to Dr. J. D. Hooker, twenty-one species have been found in Fuegia and the Falkland Islands, and one grows in matted tufts in Kerguelen’s Land. In the north the Cytopteris fragilis has been found in the seventieth parallel of latitude at Minto Inlet, and both it and Polystichum Lonchitis have been gathered at Disco, on the west side of Greenland, and Aspidium fragrans on the eastern side. On account of the extremes of heat and cold in North America there are only fifty species in all that enormous extent of country; while in Britain we are indebted to the humidity of our climate for a rich vegetation of thirty-six species, which adorn our woodlands, our valleys and mountains in wild profusion. One-half of our ferns are also native in the Himalaya mountains, where multitudes of British plants are indigenous. The fern floras of Great Britain and New Zealand are the richest in species of their respective latitudes, and have several species in common. The ferns of Tasmania are, with few exceptions, identical with those of New Zealand; and the occurrence of the rather common Australian and New Zealand Gymnogramma rutæfolia in the Pyrenees, and no where else in the whole world, so far as is known, is a remarkable fact in the distribution of plants.[70]