FILICINEM. 
429 
especially striking, from their great numbers and from being frequently flat and leaf- 
like ; the younger leaves are generally entirely covered and concealed by them. 
After these preliminary particulars, we may now turn to a consideration of the 
mode of growth of the separate organs. 
The growing end of the stem sometimes far outruns the point of attachment of 
the youngest leaves, and then appears naked, as in Polypodium vulgare, P. sporodo- 
carptwi, and other creeping Ferns, as well as in Pleris aquilina, where, according to 
Hofmeister, it frequently attains in old plants a length of several inches without 
bearing leaves. Mettenius states that in many Hymenophyllace^ leafless prolon- 
gations of the axis of this kind have been taken for roots. In other cases, on the 
contrary, especially in Ferns with an erect growth, the increase in length of the 
stem is much slower, its apex remaining enclosed in a leaf-bud. The stem generally 
ends in a flat apex ; sometimes, as in Pteris, it is even imbedded in a funnel-shaped 
elevation of the older tissues (Fig. 301, E), The apex of the stem is always occupied 
by a clearly distinguishable apical cell, which is either divided by walls alternately 
inclined, and then resembles, when viewed from above, the transverse section of 
a biconvex lens ; or it is a three-sided 
pyramid, with a convex anterior surface 
and three oblique lateral surfaces, which 
intersect behind. The outlines of the 
segments, which are in the first case in 
two, in the second case in three rows, 
or arranged with more complicated 
divergences, soon disappear in conse- 
quence of numerous cell- divisions and 
of the displacement caused by the 
growth of the masses of tissue and 
leaf-stalks surrounding the apex. The 
. c -n • • Fig. 300.— Apical view of the end of the stem of Pteris aqui- 
apical cell, lOr mStance, 01 Pteris aqUl- ^V/^i,- j^tlieaplcal cell of the stem; the apicalcell of the youngest 
, , , , leaf ; h h hair, which cover the apical region surrounded by a 
Lina, IS wedge-snapea, the segments cushion of tissue, 
on the horizontal stem forming a right 
and a left row ; the edges of the apical cell face upwards and downwards 
(Fig. 300). The same is also the case, according to Hofmeister, in Niphobolus 
chinensis and rupestris, Polypodium aureum and punctulatum, and Platycerium 
alcicorne. In Polypodium vulgare he states that it is sometimes wedge-shaped, 
sometimes pyramidal with three faces ; the last-named form occurs also in Aspidium 
Filix-?nas, &c. As a rule it may for the present be assumed that creeping stems 
with a bilateral development have a wedge-shaped apical cell, upright or ascending 
stems with radiating rosettes of leaves one that is a three-sided pyramid. 
The further relationships of the segments of the apical cell of the stem to the 
origin of the leaves and to the building up of the tissue of the stem itself are 
still but little known in detail. It cannot be doubted that each leaf results from 
a single segment only, and that this segment-cell is devoted from an early period 
to the formation of the leaf, but it appears doubtful whether the segments always 
form leaves, and if not what number of sterile segments intervenes between those 
from which a leaf is developed. 
