290 FOUNDATIONS OF BOTANY 



FERNS 



354. Structure, Form, and Habits of Ferns. The struc- 

 ture of ferns is much more complex than that of any of 

 the groups of cryptogamous plants discussed in the earlier 

 portions of the present chapter. They are possessed of 

 well-defined nbro-vascular bundles, they form a variety of 

 parenchymatous cells, the leaves have a distinct epidermis 

 and are provided with stomata. 



Great differences in size, form, and habit of growth are 

 found among the various genera of ferns. The tree ferns 

 of South America and of many of the islands of the Pacific 

 Ocean sometimes rise to a height of forty feet, while the 

 most minute species of temperate and colder climates are not 

 as large as the largest mosses. Some species climb freely, 

 but most kinds are non-climbing plants of moderate size, 

 with well-developed rootstocks, which are often, as in the 

 case of the bracken-fern, or brake, 1 and in Osmunda, very 

 large in proportion to the parts of the plant visible above 

 ground. 



355. Economic Value of Ferns. Ferns of living species 

 have little economic value, but are of great interest, even 

 to non-botanical people, from the beauty of their foliage. 



During that vast portion of early time known to geolo- 

 gists as the Carboniferous Age, the earth's surface in many 

 parts must have been clothed with a growth of ferns more 

 dense than is now anywhere found. These ferns, with 

 other flowerless herbs and tree-like plants, produced the 

 vegetable matter out of which all the principal coal beds 

 of the earth have been formed. 



1 Pteris aquilina. 



