134 Gibson . — Contributions towards a Knowledge 
incomplete character, scarcely any details being given either 
in text or plates. Moreover, he has fallen into many and 
serious errors. He has throughout made the crucial mistake 
(which others have made before him) of assuming that a section 
of the stem at any one level may stand for a section at any 
other, and that the structure of a lateral shoot-axis is neces- 
sarily the same as that of a primary erect axis or of the 
creeping rhizome. In the so-called polystelic species he has 
failed to determine accurately the course of the leaf-traces and 
the mode of anastomosis of steles at the ramifications. His 
monograph, in short, cannot be said to adequately fill the gap 
at present existing in our knowledge of this group of the 
Vascular Cryptogams, and does not compare favourably 
with the more special investigations of Treub, Vladescu, and 
others. 
The diagnostic characters of the sub-genera and species 
have, as is well known, been almost exclusively based on 
external morphological features ; and although I am far from 
desirous of minimizing the differences so emphasized, I feel 
convinced that anatomical structure, and especially the number 
and arrangement of the steles, must play some part in deter- 
mining the relationships of the species. I trust that in the 
present and succeeding papers I may be able to offer some 
data on which generalizations of value may be based with 
regard to the phylogeny of the genus and its relations to 
other Vascular Cryptogams, both recent and fossil. 
I have confined myself in the present contribution to giving 
an account of the anatomy and histology of the stem only; 
in a second paper, now in an advanced state of preparation, 
I hope to treat of the leaf, ligule, rhizophore, and root, re- 
serving the cone and sporangia for a future contribution. The 
development of the embryo has already been investigated by 
Pfefifer(l)and Hofmeister(2), whilst Millardet(3)and Belajefif(29) 
have given an account of the development of the microspore 
and its contents. The special development of the vegetative 
organs has received considerable attention at the hands of 
Treub (14), Vladescu (21), Bruchmann (18), and others. Into 
