FERNS 189 
highest, is felt to be the one between Bryophytes and 
Pteridophytes. On account of the vascular system and 
other resistant structures, the remains of ferns have been 
Fic. 181.—Cross-section of the stem (rootstock) of a fern, showing the peculiar 
vascular axis, the large xylem vessels being completely surrounded by the 
phloem. 
preserved in great abundance in the rocks. These records 
show that the ferns are a very ancient group, occurring 
in special abundance during the Coal-measures. 
Another striking fact about this leafy body of the 
ferns is that it never produces sex-organs, but does produce 
spores abundantly. This means that it is the sporophyte 
in the life-history of the fern, and when it is contrasted 
with the sporophyte of Bryophytes the differences are 
remarkable. Among the liverworts and the mosses the 
sporophyte is a leafless structure attached to the gameto- 
phyte and dependent on it, while the gametophyte is the 
leafy body doing chlorophyll work. Among the ferns, 
however, the sporophyte is an elaborate leafy structure 
and entirely independent. Therefore, when one ordinarily 
