482 



General Botany 



Fig. 297. The sensitive fern {Onoclea sensibilis), showing foliage 

 leaf and sporophylls. 



foot above the soil. In the tropics woody, erect stems give rise 

 to the tree ferns, which attain an extreme height of 60 feet. 



The roots of most ferns are comparatively small and less 

 branched than the roots of seed plants. In the herbaceous ferns 

 they arise irregularly from the sides and under surface of the 

 rhizome. In the tree ferns the root systems are more complex, 

 but they do not attain the size and spread of the root systems of 

 the seed plants. A restricted water-absorbing system is one of 

 the reasons why ferns are uncommon in dry habitats. 



Ferns multiply vegetatively by their branching rootstocks. 

 Some, like the walking fern, develop new plants at the tips of 

 the leaves when in contact with the substratum. In some trop- 



