FERNS, AND THEIR ALLIES. 1 3 



equal to half of the whole phanerogamic vegetation. 

 In receding from the tropics (where, on the large con- 

 tinents, D'Urville estimates the proportional number 

 at ^Jq) the relative frequency of ferns decreases 

 rapidly as we advance into the temperate zone. The 

 quotients are for North America and the British 

 Islands J-, for France -^g, for Germany 5V, for the 

 dry parts of Southern Italy ^\, for Greece -^f. The 

 relative frequency again increases considerably to- 

 wards the frigid north. Here the family of ferns 

 decreases much more slowly 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 Wahlenberg and Hornemann's cata- 

 logues, the relative numbers of the ferns are for 

 Lapland o^-, fo^ Iceland ^g, for Greenland ^^o." ^ 



Great favourites as are the ferns, especially for 

 decorative purposes, they are, as a whole, singularly 

 deficient in useful properties, only furnishing a kind 

 of famine food, either to man or the lower animals, 

 and not attractive for any special odour, or furnishing 

 to the arts, medicine, or commerce, any product of 

 importance. 



Tree Ferns. 



Ferns are theoretically plants without stems, with 

 a terminal vegetation, the crown continually pro- 

 ducing new fronds from its centre, whilst those at the 

 circumference fade and decay. By this continual 



' Humboldt, " Views of Nature," p. 340. 



