THE PTEEIDOPHYTES 



277 



(Fig. 228). 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 which growth is contin- 

 ued from year to year. By carefully studying the leaf scars 

 or the bases of old leaves upon the rootstock, it is usually 



FIG. 230. Diagram of a cross section of the underground stem of a fern 



The outer part of the stem is made up of hard tissue and in the interior are also 



bundles of hard tissue (s) known as sclerenchyma ; numerous woody bundles (/.&) 



are also surrounded by the large amount of pith 



possible to determine the age of the latter, that is, the age of 

 this particular fern plant. The terminal bud grows forward 

 each year from a fraction of an inch in some ferns to several 

 inches in others, and at the beginning of each season it sends 

 up one or a few new leaves. 



The rhizome of the fern presents the first really complex 

 stem structure that we find as we study the groups of plants 



