104 ELEMENTARY STUDIES IN BOTANY 



than horsetails) also have forest trees among their ancestors 

 of the Coal Age, and the appearance of these conspicuously 

 jointed trees would have been very peculiar to one familiar 

 only with trees of the present day. Many of the ancient 

 representatives of the group had foliage leaves, and in some 

 cases large ones, so that the living Equisetums are rather 

 poor representatives of the group. 



(3) Ferns (Filicales) . These are the most abundant 

 and best known of the Pteridophytes, and hardly need a 

 definition. Compared with Club-mosses, Ferns have large 

 and relatively few leaves, which bear numerous sporangia 

 upon the under surface. Not only are the leaves large, but 

 sometimes they become very large by branching. It is not 

 by its form that a fern leaf can be distinguished from other 

 leaves, but by its forking veins (Fig. 70), and by the fact that 

 it first appears as if rolled up from the tip to the base, and 

 then it expands by unrolling (Fig. 83). The leaves of Ferns 

 were once called " fronds," because they were thought to be 

 different from leaves. It was observed that they came di- 

 rectly from the ground, arising from an underground struc- 

 ture that was thought to be a root (Fig. 83) . Therefore, the 

 leaf-like structure was thought to be a combination of stem 

 and leaf, to which the name " frond " was given. Of course 

 a fern leaf is not a frond, as the underground structure re- 

 ferred to is a stem and not a root, but many still call it a frond. 



The Ferns of ordinary experience are tufts of leaves arising 

 from an underground stem (Fig. 72), which also sends out 

 roots ; but there are many tree Ferns in the tropics, the un- 

 branching trunk (often tall and slender) bearing a crown of 

 large and branching leaves (Fig. 84) ; and there are climbing 

 Ferns in our own eastern mountain region; and numerous 

 perching Ferns occur in the tropics, often covering the trunks 

 and branches of trees (Figs. 85 and 86). 



61. The strobilus. This word means " cone," and its 

 use here refers to the fact that in some Pteridophytes the 



