AND THEIR BEARING ON STELAR THEORIES FOR THE FERNS. 
721 
obvious that a deep pocket is associated with the nearest leaf-trace (text-fig. l). 
On this view endodermal cells within the stele may be regarded as new creations, 
which in some cases form foliar pockets, in others remain isolated 1 structures. But 
in all instances they provide an increased endodermal area for the stele, and may 
enhance the physiological control. 
The ancestry of the Schizasaceas is unknown, and accordingly phyletic degenera- 
tion of foliar pockets for the stock is matter of mere speculation. 
That medullation and pocketing are distinct phenomena in Schizaect dichotoma 
as in Schizasa malaccana is evidenced by the sporeling structure described by 
Boodle (3). He has traced the transition from solid protostely to medullation by 
acropetal increase of wood-parenchyma. The departure of the first leaf-traces is 
protostelic and, though pocketing is initiated, medullation is independent of it. An 
isolated endodermal spindle has also been observed in the sporeling pith. When to 
these facts is added the structural evidence already recorded from sporelings of 
Schizasa jpusilla (13), Schizasa rujpestris (ll), and Anemia phyllitidis (3), (ll), and 
from adult plants of Schizasa digitata, and Schizasa jistulosa (3), belief in the 
intrastelar origin of pith in these organisms is strengthened. 
But on the theory of the cortical origin of pith the medulla of these plants “ must 
be regarded as a derivative of the cortex which has become more or less completely 
sequestered within the stele” (37). This view, as expounded by Jeffrey (30), (33), 
finds support in histological similarity between cortex and pith. On purely histo- 
logical grounds exception may be taken to it, for the pith and cortex in both Schizasa 
digitata and Schizasa dichotoma are dissimilar. The sclerotic pith-cells of these 
species have dense mucilagenous contents, and their highly lamellated walls have 
numerous fine pits (fig. 15). Their chief duty is apparently water-storage. The 
cortical cells are mainly sclerosed : where the walls are thick, the pits are wide ; where 
the walls are thin, pitting is obscure. The contents of these cells are not apparently 
mucilagenous, and starch-storage is an evident function (fig. 14). A reasonable view 
of such facts may be that structural similarity between cortex and pith indicates 
for them like functions, while histological differences indicate functional differences. 
Thus, on histological grounds alone a cortical origin for pith cannot be deduced. 
The main prop of the theory of cortical origin of pith is, however, cortical 
intrusion. No ontogenetic evidence of actual intrusion has been advanced for the 
Schizasaceas, and a phyletic flow of cortex into the stele can only be inferred. But 
that pocketing is a result of change of procambial destination rather than a phase of 
cortical intrusion appears to be the natural interpretation of the structural facts. 
This view may be further supported from the adult stele of Schizasa dichotoma. 
Text-fig. 2 shows the general distribution of stelar tissues in longitudinal section in 
part of one of the stems examined. Certain xylic gaps have been omitted. Leaf- 
traces and endodermal pockets are reduced to one plane. As in text-fig. 1, pockets 
of diverse depth and form are shown, in some cases decurrent from the axils of 
