ILLUSTRATIONS (28). FERNS. 339 



Between the tropics, where, on the declivities of the Cor- 

 dilleras, climates are superimposed in strata, the true region 

 of arborescent ferns lies between about 3200 and 5350 feet 

 above the level of the sea. In South America and in the 

 Mexican highlands they seldom descend lower towards the 

 plains than 1280 feet. The mean temperature of this happy 

 region is between 64.6 and 70. 8 Fahr. It reaches the 

 lowest stratum of clouds (which floats the nearest to the 

 surface of the sea and the plain), and it therefore enjoys 

 uninterruptedly a high degree of humidity, together with a 

 great equality in its thermal relations.* The inhabitants, who 

 are of Spanish descent, call this region " Tierra templada de 

 los helechos." 



The Arabic designation for ferns is fdedschun, filix, (from 

 which the f has been changed, according to Spanish usage, 

 into A,) and perhaps the term may be connected with the verb 

 faladscha, "it divides," from the finely cut margin of the frond, f 



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 

 Die men'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 Labillardiere in Tasmania: a Thyr- 

 sopteris 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 52 J 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 (FUices^ in gene- 

 ral flourish, are manifested in the numerical laws of their 



* Kobert Brown, In Expedition to Congo, Append, p. 423. 

 f Abu Zacaria Ebn el A warn, Libra de Agr cultura, traducido por 

 J. A. Baiiqueri, t. ii. Madr. 1802, p. 736. 



z 2 



