FERNS 



185 



plant oj considemble size and consisting of root, stem, and leaves 

 with spores, and the other being very small and developing sexual 

 organs from Jhe seeds of ivhich tJie first type again grows. 



4. Distribution and Classification. — This large order of plants 

 is represented in nearly all parts of the earth, but in the tropics, 

 and there especially on islands and coast tracts, they grow with 



Fig. 1G9. — A group of tropical Ferns. 



greatest luxuriance (tig. 169). The arrangement and structure 

 of the fruit-clusters on the fronds are the characteristics by 

 which the Ferns are classified. They are roundish, uncovered 

 and scattered on the under surface of the fronds: in the genera 

 Poly podium (compare the epiphytical P. quercifolitim, fig. 170) 

 and Gleichenia; — seated on the margin of the fronds and covered: 

 in Pteris, Adiantum, and the creeping Lygodium; — cup-shaped 



