THE FERNS 



539 



Fig. 366. — Fern Stems {Aspidiuni sjjp.). A, underground stem {rhizome) 

 of A. Filix-mas with rind removed to sho\y the net-worli of fibrovascular 

 bundles. B, one mesh of this nct-worlv enlarged to show the branches 

 which enter a leaf to form its framework. C, cross-section of a rhizome 

 (■4. corioceu}n) slightly enlarged to show the cylindrical fibrovascular 

 system formed of two main strands, the upper (o) smaller than the 

 lower (n), and the finer branches of these which enter the leaves. D, the 

 fibrovascular cylinder of the same, removed and laid out flat after 

 splitting the lower strand (u, u) in halves, lea-\'ing the upper strand (o) 

 in the middle unbroken, as also the finer strands {b, b, b, b) which enter 

 leaves and roots, and the larger strands (x, j, .r, x, x) which enter 

 branches of the stem. (Sachs, IMettenius.) 



of simpler .structure it was sufficient to distinguish merely diiTerent 

 tissues, in the higher plants the differentiation has progressed so 

 far that iisaue systems must be recognized. Thus we have a tegu- 

 mentanj system, consisting of the epidermis and its outgrowths, a 

 vascular system compri.sing the vascular bundles, and a fundamental 

 systern consisting mainly of parenchj'ma and including meristem, 

 the green cells accessible to light, and the pith-like internal parts 

 in which food is stored. 



The stem of an Aspidium (Fig. 170) as of nearly all our nati-^^e 

 ferns, remains mostly underground as a more or less horizontal 

 rhizome. A considerable amount of starch stored over the winter 

 m the fundamental tissues of this perennial organ, accounts for the 

 rapid unfolding of the leaves in spring. Some of the leaves are 

 entirely vegetati\T; other leaves bear numerous minute sporangia 

 in clusters upon the back, each cluster being covered bj' a shield- 

 like out-growth (Figs. 170, S-5). A peculiar part of the sporangium 

 is a ring of thickened cells running along the back (6c) , which when 



