MOSSES, LIVERWORTS, AND FERNS 



271 



256. The rootstock of a fern. If the soil is carefully removed 

 from the underground part of one of the common ferns, the 

 horizontal rootstock (rhizome) appears (fig. 208). The lower 

 side of the rhizome gives rise to the roots, and the upper side 

 bears the leaves. At the tip of the rootstock is the bud, by 

 means of wliich growth is continued from year to year. The 

 leaf scars, or the bases of old leaves, 



may usually be seen upon the root- 

 stock. The terminal bud grows 

 forward each year from a fraction 

 of an inch in some ferns to several 

 inches in others, and at the begin- 

 ning of each season it sends up 

 one or more new leaves. 



The rhizome of the fern (fig. 209) 

 presents the first really complex 

 stem structure that we find as we 

 study the groups of plants in the 

 order of their increasing complex- 

 ity. This is a woody stem com- 

 posed of several kinds of stem 

 tissues. Some of these tissues are 

 heavy-walled and give rigidity to 

 the stem. The rhizome is some- 

 times stored full of food in the 

 form of starch. Some of the tissues 

 consist chiefly of rounded, fiber- 

 like bundles which extend length- 

 wise throughout the stem. These are the fibrovascular bundles, 

 which term simply means " fibrous bundles of vessels." 



257. The leaf of a fern. As a fern leaf develops from the 

 bud, it unfolds in a very peculiar fashion (fig. 211) known 

 as circinate vernation. The coiled or rolled (circinate) tip of 

 the leaf is easily seen even in most old fern leaves. Mature 

 fern leaves assume so great a variety of forms that it is impos- 

 sible to give any description that holds good for many kinds, 



FIG. 208. The bracken fern 

 (Pteris aquillna) 



The rootstock (rh) is horizontal 



and grows underground ; upon it 



are the huds (b) and the upright 



leafstalk (at) 



