540 Holden . — Jtirassic Coniferous Woods from Yorkshire . 
Metacedroxylon latiporosum (Figs. 32-24). 
Another closely allied species is shown in Figs. 22-24. The lack 
of wood parenchyma, presence of thick-walled, heavily pitted rays, and 
Araucarian pitting of the tracheides clearly affiliate it with Metacedroxylon . 
In many places the ordinary compressed tracheary pitting becomes accen- 
tuated, until a condition is reached like that shown in Fig. 24. This type 
is similar to that of Xenoxylon latiporosum , and on that account it is 
proposed to call this wood Metacedroxylon latiporosum. In Xenoxylon it 
seems evident that the large pits of the tracheides are formed by the 
extreme compression of a single row of approximated pits. In this speci- 
men, however, the not infrequent substitution of a pair of small opposite 
pits for a single large one indicates another mode of origin. In fact, 
there seems to be no reason why such pits could not have been formed 
in two ways — either by the horizontal enlargement of a single pit, or the 
fusion of a pair of opposite pits. 
Br achy oxy Ion sp. (Figs. 25 and 26). 
Among both the lignites and petrified material, there were numerous 
specimens conforming more or less closely to the Brachyoxylon type. 
Figs. 25 and 26 show the structure of one of the lignites. A noticeable 
peculiarity of this wood is the angle at which the rays cross the tracheides 
(Fig. 25). This feature seems to be constant, since it was found in several 
specimens. It is evident that the rays are smooth and unpitted on horizontal 
and end walls, with one or two piciform pits on each radial wall. The 
tracheary pits are either circular and scattered or flattened and compressed 
(Fig. 26). Not infrequently they occur in sub-opposite pairs, but in no 
instance is there any indication of cellulose bars of Sanio. 
Another variety of Brachyoxylon is shown in Fig. 27. This specimen 
has scattered pits and thin-walled rays, but is unique in the possession 
of large numbers of septate tracheides at the beginning of each annual ring. 
The significance of these cells it is difficult to infer. Whether they repre- 
sent incipient parenchyma, or are related to an injury, it is impossible to say, 
but the latter supposition is rendered improbable by their appearance 
in several successive years, and the lack of any twist in the grain which 
would indicate proximity to a wound. 
Of the other specimens of Brachyoxylon none presented any especial 
features of interest, beyond the fact that in one there were medullary stone 
cells. 
Araucarioxylon sp. (Fig. 28). 
Among the lignites was one clearly defined Araucarioxylon. This is 
shown in Fig. 28. The tracheides have one or two rows of closely com- 
pressed, flattened pits, the rays are low, thin-walled, and highly resinous, 
