The Fems and Their AlHes 



285 



Fig. 168. A large tropical fern (Marratia), with leaves over 30 feet in length. 

 Philippine Islands. 



The ferns. The ferns are noted for the large size of their 

 fohage leaves. In temperate regions these leaves are much 

 branched and in some species attain lengths of from 3 to 6 

 feet. They usually rise from imderground stems, which may 

 be long, slender, and horizontal or short, thick, and upright. 

 The venation of the leaves differs from that of seed plants 

 in being forked ; that is, each vein divides into two smaller 

 ones, and each of these subdivides in the same manner. The 

 root systems of the ferns are all small and scantily branched as 

 compared with those of the seed plants. This is probably 

 the reason why ferns as a rule are confined to moist habitats. 



In the moist tropics there are many species of tree ferns 

 with upright columnar stems bearing a rosette of leaves at 

 the summit. The stems may attain heights of from 10 to 

 50 feet, and they bear leaves 5 to 15 feet in length. 



The equisetums, or horsetails. In swamps, on the banks 

 of streams, and on raUroad embankments one can find slender, 



