fli / 
7 Mk 
Ce ’ y, * ‘ 
” oi i ts Ppa 
a12 ag tructural and Ph iysiological Botany. 
of parenchyma which also contains starch, and of base. tubes ; 
and sieve-tubes (Fig. 438 I1.). 
The leaves of Ferns are commonly known as s fronds. 
They originate, like those of higher plants, as small cellular 
elevations beneath the 
‘punctum - vegetationis ;’ 
but increase in length, like 
branches, at their apex, 
below which the lamina is 
then formed. The leaves 
are rolled up, when young, 
in a circinate manner ; after 
maturity, they are ioe 
off periodically. They are 
| roduc nly at the apex 
-Fic. 438 I1I.—Transverse section through P od ed O y tne Pp 
the stem of a tropical Fern ; a @ layers of of the stem. Their form 
lignified nearly solid parenchymatous ‘ 
cells, surrounding the vascular bundle c ; varl1es greatly, from lanceo- 
x5 the points of attachmentof fiveleaves Tate and entire in the harts- 
tongue, Scolopendrium, to 
doubly or trebly pinnate in the Aspzdiums. Except in the 
Hymenophyllacez they are almost always composed of 
several layers of cells, which very commonly separate into 
two clearly distinguishable laminz, the upper one consisting 
of cylindrical cells placed vertically to the surface, and fit- 
ting more or less closely to one another, the lower of a looser 
tissue formed of cells of a more spherical form. Both sides 
of the leaf are covered by an epidermis provided with nume- 
rous stomata. The stem and the rachis of the leaves are 
clothed, in most species, with brown dry lanceolate or hair- 
like epidermal structures of a thin membranous texture, the 
palee. 
The sforangia are arranged in masses at definite spots, 
usually on the under side of the leaf, and are outgrowths of 
its epidermis (Fig. 439). The separate sor¢ [or collections 
of sporangia] vary in form and arrangement, and afford dis- 
tinguishing characteristics for the genera. They are round- 
