THE FERNS 539 
“ll 1 4 
Att Vit Pe le 
Ae 
DY ) 
Fic. 366.—Fern Stems (Aspidium spp.). A, underground stem (rhizome) 
of A. 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. coriaceum) slightly enlarged to show the cylindrical fibrovascular 
system formed of two main strands, the upper (0) 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, leaving the upper strand (0) 
in the middle unbroken, as also the finer strands (6, b, b, b) which enter 
leaves and roots, and the larger strands (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 system comprising the vascular bundles,-and a fundamental 
system consisting mainly of parenchyma 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 native 
ferns, remains mostly underground as a more or less horizontal 
rhizome. A considerable amount of starch stored over the winter 
in 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 
