FILICINEM 
435 
parent root. The cortex of the parent root is simply broken through, no root-sheath 
being formed. 
The Trichomes of Ferns assume a great variety of forms. True root-hairs, 
simple unarticulated tubes, arise, not only on the roots themselves, but also on 
underground stems and on the bases of leaf-stalks (as in 
Pteris aquilina and Hymenophyllaceae). On aerial creeping 
stems and on the leaf-stalks the numerous usually brownish 
or dark-brown flat multicellular hairs, the PalecE or Ramenta^ 
occur, soon becoming dry, often entirely enclosing the buds, 
and attaining a length of from i to 6 cm. (as in Poly- 
podium, Cibolium, Sec). Long strong bristles are sometimes 
found on the lamina (in Acrostichum criniiuni), and very often 
fine, delicate, articulated hairs. They are formed from single 
superficial cells at the growing-point. 
The Sporangia of Ferns are small rounded capsules, which 
are borne on long stalks in the Polypodiaceae and Cyatheacese, fig. sos.-under-side 
of a lacinia of a leaf of 
but which are sessile in other Ferns. The wall of the sporan- Aspidimn Fiux-ynts, 
witli eig'ht indusia i 
gium, when mature, consists of but a single layer of cells. A (X2). 
ring of cells belonging to the wall of the capsule and running 
across it transversely or obliquely or lengthwise is generally developed in a peculiar 
manner, and is then termed the Annulus. By its contraction when dried up the 
capsule bursts at right angles to the plane of the annulus. Sometimes, instead 
of the annulus, a terminal or lateral group of the cells of the wall of the capsule 
is developed in a similar manner. 
The sporangia are generally combined into groups, each group being termed a 
Sorus; the sorus contains either a small definite number or a large indefinite 
number of sporangia, and among them also very commonly some slender articu- 
lated hairs, the Paraphyses. The whole sorus is very generally covered by an 
excrescence of the epidermis, the true Indusium^ : in other cases the indusium 
consists of an outgrowth of the tissue of the leaf itself, and is then composed of 
several layers, and even has stomata ; or the covering of the sorus is simply the 
result of the margin of the leaf being recurved or rolled over it : in these cases the 
indusium is said to be false. In Lygodium each separate sporangium is covered by a 
pocket-shaped growth of the tissue of the leaf like a bract. Sori are not usually 
formed upon all the leaves of the mature plant; sometimes groups of fertile and 
sterile leaves alternate in regular succession, as in Struthiopteris gerjiianica. In some 
cases the sori are uniformly distributed over the whole of the lamina, in others they 
are connected with definite portions of it. The fertile leaves may be in other 
respects like the sterile ones, or they may be strikingly diff'erent from them ; and 
this difference is not unfrequently occasioned by the partial or entire failure of deve- 
lopment of the mesophyll between and near the fertile veins ; the fertile leaf, or the 
fertile part of the leaf, then appears like a spike or panicle furnished with sporangia 
(f. g. Osniunda, Aneimia). The sporangia generally arise from the epidermis of the 
^ [On the development of the indusium, see Prantl, Die Hymenophyllaceen, 1875, and die 
Schizgeaceen, i88i ; Burck, Over de ontwikkelingsgeschidenis van het indusium der Varens, 
Haarlem [874.] 
F f 2 
