780 
Notes . 
cylinder; but that the latter becomes at first a concentric fibro -vascular 
tube ( Biindelrohr of De Bary), with gaps for the branches alone, or 
with gaps for both leaves and branches. 
The tubular nature of the central cylinder in the polystelic type 
may become subsequently disguised by the overlapping of the gaps 
and by the appearance of medullary strands, derived in all the cases 
investigated by the writer from the inner wall of the stelar tube. It 
seems better to describe these conditions as adelosiphonic instead of 
polystelic, since the latter term implies a misconception. 
In the Osmundaceae the writer believes he has found evidence of 
the derivation of the medullated monostelic and astelic types from the 
siphonostelic condition with internal phloem by the degeneration of 
the latter. 
Osmunda cinnamomea shows all stages between the polystelic and 
astelic conditions; O. regalis still retains occasionally a brown 
sclerenchymatous pith, while in 0. claytoniana this phenomenon is 
quite absent. Similar examples of degeneracy are found among 
the Polypodiaceae. Potoni£ further believes that the so-called 
medullated monostelic central cylinder of the Gymnosperms is derived 
by degeneracy of the internal phloem from such types as Medullosa. 
The writer considers that there is good evidence for regarding the 
so-called medullated monostelic type of central cylinder as derived by 
specialization, accompanied by degeneracy, from the so-called poly- 
stelic type of Van Tieghem, and thus returns to the conception of the 
morphology of fibro-vascular strands set forth in De Bary’s ‘ Compara- 
tive Anatomy/ 
The study of the development of the fibro-vascular skeleton of the 
higher plants seems to lead to the conclusion that this is hardly less 
important phylogenetically than the osseous skeleton has proved to be 
in the case of vertebrated animals. Where the tubular central cylinder 
exists there are two main types, the phyllosiphonic, where foliar gaps 
are constantly present, and the cladosiphonic, where foliar gaps are 
equally constantly absent. The central cylinder of the Filicales, 
Gymnosperms, and Angiosperms belongs to the former type, and that 
of the Lycopodiales and Equisetales to the latter. These distinctions 
appear to be of special importance, on account of the absence of 
constant and far-reaching criteria of taxonomy among the vascular 
plants. They moreover agree closely with evidence drawn from other 
available sources. 
