Possible Existence of a Lattice-Work Fern Stem. 213 
still remain undisturbed. For this, in my opinion, lies chiefly in 
the phylogenetic significance attached to the idea that has led to 
the derivation of the various types of vascular system from a 
primitive protostele, and renders it necessary that an attempt 
should he made in each particular case to reconstruct in detail the 
series of phylogenetic modifications that have produced the type in 
question. With this object in view the nature and origin of all 
internal endodermes, ground tissues, etc., becomes a matter of 
considerable importance, and they therefore deserve the most 
careful investigation. It also becomes necessary to draw a clear 
distinction between s'uch of these internal tissues as have been 
from their first appearance always in direct continuity with the 
corresponding tissues on the outside of the protostele, and those 
which were altogether central in origin, and have either remained 
entirely distinct from the corresponding external tissues, or only 
became continuous with them at a later period in their history. 
It is evident that the aforesaid changes in the structure of the 
vascular system described above are due chiefly, if not entirely, to 
the influence of the leaf-traces, and that they advance in measure 
as the importance and size of the leaf-trace increases relative to 
that of the stem. It follows naturally that a change in the relative 
importance of the vascular supply of the leaf and that of the stem 
should correspond to a similar change in the relative importance 
and predominance of the leaf and stem as a whole. It is also 
reasonable to suppose that the increasing importance of the leaf as 
a whole, if carried beyond a certain degree, might express itself 
upon the structure of the solid axis of the stem in a manner 
similar u to that in which the increasing importance of the leaf- 
trace expressed itself upon the originally solid vascular cylinder of 
the stem. These considerations appear to me to throw an interest¬ 
ing light upon the somewhat peculiar type of stem structure 
possessed by a few ferns of which Onoclea germanica W. may be 
taken as a good example. 
If a series of transverse sections passing through several con¬ 
secutive nodes and internodes in a well-grown erect stock of Onoclea 
germanica be made, attention will at once be drawn to the fact that 
the continuity of the plates of tissue that form the sections is inter¬ 
rupted by a number of holes or lacunae (figs. 41 and 42). These 
lacunae are lined by the epidermis of the stem, and if followed 
upwards through the series of sections they will be found to com¬ 
municate with the exterior just above the point of insertion of the 
