ANNOTATIONS AND ADDITIONS. 357 



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 -f j} for France -fjj'foT 

 Germany J^, for the dry parts of the south of Italy j\, and for 

 Greece j\. Towards the colder regions of the north we see the re- 

 lative frequency increase again rapidly ; that is to say, the number 

 of species of ferns decreases much more slowly than does the num- 

 ber of species of phamogamous plants. At the same time, the lux- 

 uriance, abundance, and mass of individuals in each species augments 

 the illusive impression of absolute numbers. According to Wahlen- 

 berg's and Hornemann's Catalogues, the relative numbers of Filices 

 are, for Lapland ^ T) for Iceland -j'g-, and for Greenland y 1 ^. 



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 organization by which fruc- 

 tification is effected. He distinguishes a bisexual arrangement in the 

 ovule-like cell on the middle of the theca, and in the ciliated anthe- 

 ridia or spiral threads before examined by Nageli. The fertilization 

 is supposed to take place not by pollen tubes but by the movable 

 ciliated spiral threads. (Suminski zur Entwickelungs-geschichte der 

 Farrnkrauter, 1848, s. 10-14.) According to this view, Ferns, as 

 Ehrenberg expresses it (Monatl. Berichte der Akad. zu Berlin, Ja- 

 nuar 1848, s. 20), would be produced by a microscopic fertilization 

 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. 



( a9 ) p. 244. "Liliacese." 



The principal seat of this form is Africa, where it is both most 

 varied and most abundant, and where these beautifully flowering 



