68 On the Structure and Affinities of KJ^llAurfim^ 
fibre witli which I am acquainted. The fibres are unusually large, 
having constantly a diameter of from ^Jq- to 4^0- of an inch. The 
reticulations cover the surface of the fibre, each areola being from 
T^Vo to 2-oVo- of an inch in diameter. 
Fig. 4 represents part of a tangential section exhibiting the 
surfaces of two fibres parallel to the exterior of the plant. The 
fibres are separated by one of the large medullary rays, with its 
multiphed vertical rows of cells, and which constitute one of the 
striking features of this remarkable species. This section demon- 
strates what I have already affirmed, viz. that the reticulations 
cover equally the entire circumference of the interior of the tube, 
and are not confined, like the areola of coniferous fibres, to its 
lateral surfaces. These two figures represent reticulated fibres as 
seen in several distinct plants found in the Coal-measures. Whether 
these prove to be difierent species of one genus, or whether they 
will require more than one genus for their reception, remains to be 
seen. But certainly none of them can be regarded as Dadoxylons, 
since they belong to an altogether difierent type of structure. In 
the general arrangement of their tissues, whether of pith, wood, or 
bark, they correspond very closely with the true conifera, but we 
have no evidence that they were conifers. 
Since these plants with reticulated fibres can no longer be 
recognized as Dadoxylons, they must either be assigned to some 
other existing genus, or have a new one instituted for their re- 
ception. The only existing genera which approach them are 
Palaeoxylon and Pissadendron — the first of which was founded by 
Witham, and the last by Brongniart, for the reception of some 
of Witham's plants. All these are described by Brongniart as pos- 
sessing true coniferous fibres, which, if correct, would exclude the 
specimens under consideration. It is possible that some of the 
former may belong to reticulated types — especially Palaeoxylon — 
but, since they are not so defined by the founder of the genera, 
they must for the present be left amongst the conifers, though they 
may be doubtful ones. 
It appears necessary, therefore, to estabhsh a new genus for all 
the plants whose woody cylinders consist of reticulated fibres; 
and the name of Dictyoxylon appears an appropriate one for it. 
I should propose for the present to include in this genus all the 
reticulated types — whether their medullary rays consist of one or 
of several vertical series of cells. At some future time their further 
separation into two or more genera may be requisite. 
I have already called attention to the fact that the hexagonal 
and almost circular discs of the fibres of Dadoxylon (Fig. 1) 
exhibit a plane surface, the central dot common in recent conifers 
being absent. The absence of this dot led the late Kobert Brown, 
some years ago, to reject my conclusion, that the fibres in question 
