340 VIEWS, &C. PHYSIOGNOMY OF PLANTS. 



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, ^L 

 of all the phanerogamia, and in mountainous districts of large 

 continents -g- to -|-. 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 phanero- 

 gamic plants increases so considerably, that in the South-Sea 

 Islands the quotient rises to \, while in the sporadic islands, 

 St. Helena and Ascension, the number of ferns is almost equal 

 to half of the whole phanerogamic vegetation.* In receding 

 from the tropics (where on the large continents d'Urville esti- 

 mates the proportional number at -^), the relative frequency 

 of ferns decreases rapidly as we advance into the temperate 

 zone. The quotients are for North America and the British 

 Islands y^, for France -^, for Germany y'y, for the dry parts 

 of Southern Italy yz , for Greece -g^-. 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 im- 

 pression of absolute frequency. According to \Vahlemberg's 

 and Hornemann's catalogues, the relative numbers of the 

 Filices are for Lapland -^y, for Iceland -^ T , for Greenland y^-. 

 Such are, according to our present knowledge, the natural 

 laws that manifest themselves in the distribution of the grace- 

 ful 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 dis- 

 covered an organisation capable of effecting fructification in 

 the prothallium of ferns. He distinguishes two sexual appa- 

 ratuses, 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 Nageli. Fructification 



* See a valuable Treatise by d'Urville, Distribution geographique 

 desfougeres sur la surface clu Globe, in the Annates des Sciences nat.j 

 t. vi. 1825, pp. 51, 66, 73. 



