Possible Existence of a Lattice-Work Fern Stem. 215 
are no epidermal pockets. However, where the stolon thickens out 
to form the erect stock the epidermal pockets begin to appear; at 
first one only in each transverse section (fig. 43) then rapidly 
increasing in number as the leaves become crowded together. 
Onoclea sensibilis L. also possesses epidermal pockets but they 
are much less conspicuous than in O. germanica, and they barely 
reach so far as the central ground-tissue. They appear in the 
sections as narrow concentric slits and the leaves are inserted so 
far apart that only one pocket is present at a time. 
Fig. 43. 
Fig. 44. 
Fig. 45. 
Fig. 43. Onoclea germanica. Transverse section of a stolon where 
it enlarges to form an erect stock. 
Fig. 44. Cystopterisfragilis. Transverse section of the stem. 
Fig. 45. Aneimia Phyllitidis. Transverse section of thestem. 
One epidermal pocket is just about to appear at X. 
The stem of Cystopteris fragilis Bernh. furnishes almost as 
good an example of the development of epidermal pockets as Onoclea 
germanica itself, although the whole structure is on a smaller scale. 
Not more than three pockets were found in any one transverse section 
(fig. 44), but they are relatively large and run downwards for about 
4 man. reaching clearly into the internal ground-tissue. The 
suggestion that the axis of the plant is merely a series of leaf bases 
inserted one upon the other is even more striking than in Onoclea 
germanica for the vascular lattice-work of the stem is a very loose 
one with relatively large gaps. 
Typical epidermal pockets are also to be found in Aneimia 
phyllitidis Sw. and A. hirta Sw. Not more than three of them 
occur in any one section, and they are more or less crescentic in 
form (fig. 45). Although less conspicuous than those in Onoclea 
germanica they reach well into the central ground-tissue within the 
vascular ring ; indeed, in some cases they were still visible on the 
inner side of the leaf trace even after the latter had joined on to 
the meristeles of the stem. In one specimen of Aneimia phyllitidis 
that I examined the slender first-formed region at the base of the 
■ 4' . 
