Hymenophyllaceae , Schizaeacecie and Gleicheniaceae . 519 
Endodermal pockets, if they occurred alone, need not, 
according to our present knowledge, affect the question of the 
phylogenetic history of the stelar structure, for they may 
penetrate a solid stele as in the case of Lindsay a, described 
by Tansley and Lulham and referred to above. That is 
to say, so far as one knows, they need not be vestigial struc- 
tures, but might perhaps arise for mechanical reasons 1 . Thus 
no certain conclusion can be drawn from the presence of 
endodermal pockets alone. 
The isolated internal endodermis, however, is difficult to 
explain except as a reduced structure. An argument which is 
practically based on the apparent impossibility of attributing 
a function to a given structure in its present condition is natur- 
ally inconclusive, but absence of function is also suggested 
by the apparently hap-hazard occurrence of the structure in 
question (without definite relation to nodes or branching). 
Under these circumstances the following views are brought 
forward, while fully recognizing the tentative nature of some 
of them. 
1. The internal endodermis described above, being isolated 
and apparently functionless, is probably reduced from some 
better developed structure. 
2. Where the internal endodermis is best developed, it may 
be regarded as least reduced. And, as in that case it encloses 
two kinds of elements similar to the cells of the inner and 
outer cortex respectively, there is some probability that these 
two tissues were at one time (in the phylogenetic history) con- 
tinuous with the cortex 2 3 , on the ground that continuity 
1 It is conceivable that certain strains, liable to occur in the leaf-trace (perhaps 
before the sclerification of the cortex), might be capable of tearing the endodermal 
sheath of the vascular system at its ‘axillary’ point, while the elongation of this 
part of the endodermis as a hollow tapering tube dipping into the stele might pre- 
vent rupture between endodermal cells. The fact that leaf-traces, which leave the 
stele nearly at right angles instead of at a more acute angle, do not have well- 
developed endodermal pockets, may have some such significance, though it would 
not, on the other hand, be incompatible with a vestigial nature of the endodermal 
pockets. 
3 Such continuity would prove nothing as to the homology of the tissues 
concerned. 
