THE FERNS 



539 



Fig. 366. — Fern Steins {Aspidium spp.). A, underground stem (rhizome) 

 of .4. Filix-mas with rind removed to show the net-work of fibrovascular 

 bundles. B, one mesh of this net-work enlarged to show the branches 

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

 {A. corioceum) slightly enlarged to show the cylindrical fibrovascular 

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

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

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

 splitting the lower strand (u, u) in halves, leaving the upper strand (o) 

 in the middle unbroken, as also the finer strands (6, 6, h, h) which enter 

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

 branches of the stem. (Sachs, Mettenius.) 



of simpler structure it was sufficient to distinguish merely different 

 tissues, in the higher plants the differentiation has progressed so 

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

 mentary system consisting of the epidermis and its outgrowths, a 

 vascular systetn comprising the vascular bundles, and a fundamental 

 system consisting mainly of parenchyma and includiBg 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 native 

 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 vegetative; other leaves bear numerous minute sporangia 

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

 like out-growth (Figs. 170, 3-5). A peculiar part of the sporangium 

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



