244 ELEMENTS OF BOTANY. 
FERNS. 
303. Structure, Form, and Habits of Ferns. —The structure 
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 
fibro-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 
* Fic. 208. — Prothallia of a Fern (Aspidium Filiz-mas). 
A, lower side of prothallium; ar, archegonia; an, antheridia; rh, root-hairs ; 
B, prothallium producing a young fern plant; b, the first leaf; w, the root, 
(Magnified about 8 diameters.) 
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 
