1908-9. ] THE STELE OF OSMUNDA CINNAMOMEA. 531 
to botanical science in demonstrating the existence of the Osmundaceous 
type at such an early period. But it is extremely doubtful if their paleo- 
botanical studies have as yet indicated in any way the course of evolution 
of the siphonostele from the protostele in the Osmundacee. Indeed, a 
very obvious conclusion to be drawn from their account would seem to be 
that even the Permian and Mesozoic siphonostelic members of this family, - 
so far as they are known, possessed essentially the same specialized fea- 
tures that are characteristic of modern forms. 
The facts in hand are believed to substantiate the hypothesis that 
the ancestral Osmundacee possessed a typical filicinean amphiphloic 
siphonostele. As an adaptation to the conditions of the habitat, the 
outer cortex became thickly sclerified, and as a co-relation, the central 
pith. As a further adaptation, there may have been a thickening pith- 
wards of the wall of the cylinder of xylem, made necessary by the needs 
of fronds that had suffered insufficient reduction or none at all. This 
might have involved the formation of pockets in the wall and the narrowing 
of leaf-gaps, with eventually the loss of the connections between internal 
and external phloems, and endodermis. The next step in reduction was 
the loss of internal phloem and then of internal endodermis. It is possible 
to conceive that in some cases, either before or after this stage, the medul- 
lary rays and even the parenchyma pockets may have been completely 
obliterated. The whole gamut of reductions may have been run through 
in any geological age in any genus. ‘The living genera are the offshoots 
of more or less reduced ancestors. Their seedlings do not repeat every 
phylogenetic stage, and exposed as they are to much the same environ- 
ment as the adult, exhibit the same type of adaptation. 
SUMMARY. 
1. The cortical cells at the base of the seedlings of Osmunda cin- 
namomea examined were occupied by a fungus: 
2. Individual plants vary considerably among themselves in regard 
to the details of their development. But in no instance is the transition 
from the protostele to the siphonostele effected by a simple expansion as 
has been claimed to be characteristic of the Osmundacee. ‘There are 
bays or gaps in the xylem (often anticipated below the nodes by paren- 
chyma pockets) in the neighbourhood of the nodes, and eventually the 
edges of the xylem close around the upper end of one of these gaps, the 
parenchyma thus enclosed constituting a “‘stelar’”’ pith. ‘The internal 
endodermis and ‘‘extrastelar’”’ pith arise as an eccentrically situated 
pocket at the inner entrance to a leaf-gap. They do connect with the 
