XX] RECENT FERNS 307 



dicotyledonous foliage, but the compound leaves of many dicoty- 

 ledons, e.g. Paullinia thalictrifolia (Sapindaceae) and species 

 of Umbelliferae, may easily be mistaken for fronds of ferns. 



The dichotomously lobed lamina of some Schizaeas, e.g. 

 S. dichotoma and S. elegans (fig. 222), bears a close resemblance 

 to the leaves of Baiera or Ginkgo^. The original description by 

 Kunze^ of the South African Cycad Stangeria paradoxa as a 

 Polypodiaceous fern illustrates the difficulty, or indeed impossi- 

 bility, of distinguishing between a sterile simply pinnate fern 

 frond and the foliage of some Cycads. The deeply divided 

 segments of Cycas MichoUtzii^ simulate the dichotomously 

 branched pinnae of Lygodium dichotomum, and the leaves of 

 Aneimia rotundifolia (fig. 223) and other species are almost 

 identical in form with the Jurassic species Otozamites Beani, 

 a member of the Cycadophyta. 



There are certain facts in regard to the geographical dis- 

 tribution of ferns to which attention should be directed. Mr 

 Baker in his paper on fern distribution writes: "With the 

 precision of an hygrometer, an increase in the fern-vegetation 

 marks the wooded humid regions*." If in a collection of fossil 

 plants we find a preponderance of ferns we are tempted to 

 assume the existence of such conditions as are favourable to the 

 luxuriant development of ferns at the present day. On the 

 other hand, we must bear in mind the wonderful plasticity of 

 many recent species and the fact that xerophilous ferns are by 

 no means unknown in present-day floras. 



Ferns are admirably adapted to rapid dispersal over com- 

 paratively wide areas. Bower ^ estimates that in one season 

 a Male Fern may produce about 5,000,000 spores: with 

 this enormous spore-output are coupled a thoroughly efficient 

 mechanism for scattering the germs and an unusual facility 

 for wind-dispersal. When Treub^ visited the devastated and 

 sterilised wreck of the Island of Krakatau in 1886, three years 

 after the volcanic outburst, he found that twelve ferns had 

 already established themselves; the spores had probably been 



1 Seward and Gowan (00). = Hooker (59). 



3 Thiselton-Dyer (05). •* Baker (68) p. 305. 



5 Bower (08) p. 18. « Treub (88) A. ; Ernst (08). 



