449 
Scott.—The Structure of Mesoxylon rnultirame . 
a single strand all through. The tissue in the middle of the stele is pith, 
and that at its sides wood. There are slight irregularities in the distribution 
of the tracheides, but no sign of stem-wood interrupting the continuity of the 
tissues of the axillary stele. The next section below shows a pith-bay and 
median strand, just as in other cases where a stele has entered. 
It thus appears that the division of the axillary stele inwards is an in¬ 
constant character of little importance ; only its connexions with the stem- 
wood are essential. Very little is shown in this specimen of the axillary 
shoots when free from the stem. An example in the first section of the 
transverse series (2760) has a flattened stele with little secondary wood, and 
appears to be similar to the shoots so well represented in the type. 
One or two points may be mentioned in which this specimen supple¬ 
ments the results obtained from the investigation of the type, as regards 
wood and bast . The pitting on the radial walls of the cells of the rays is 
fairly shown in places. The number of pits in the ‘ field 5 (i. e. in the area 
where a ray-cell crosses a single tracheide) is from three to six ; these pits 
are elliptical, often oblique, and appear to be simple (PI. XIV, Fig. 25, m.r.). 
A point of interest is the presence of pits on the tangential walls of 
some of the tracheides, especially as the occurrence of tangential pits in 
Palaeozoic woods has recently been denied (Jeffrey, 1917 , p. 49). They are 
clearly shown in PL XIV, Fig. 24, from a tangential section through the outer 
part of the wood. Sometimes they form a single row, sometimes two or 
more ; in the latter case they are sometimes very oblique. They are only to 
be found on a few tracheides, as is shown in transverse sections where the 
pitting can be distinguished with sufficient clearness to show its distribution. 
Tangential pits in Pitys antiqna were described and figured in 1902 
(Scott, 1902 , p. 352, PI. VI, Fig. 20), but do not seem to have been often 
met with as yet in wood of Palaeozoic age. 
Another feature shown in the specimen under consideration is the 
presence of wood-parenchyma, which appears at several places. The strand 
shown in Fig. 25 lies at a distance of about 3 mm. from the pith. It con¬ 
sists of a long vertical row, in part double, of cells with transverse walls. 
Their length here ranges from about too to 200 /x, with a width of 36-48 /x. 
Where the diameter appears about twice as great (84 /x) it is possible that 
longitudinal walls may have broken down. Many of the cells have dark, 
perhaps resinous contents. Similar rows of cells occur at other places 
farther out in the wood. Sometimes the individual cells reach a length of 
about 430 /x. The cell-walls are rather thinner than those of the tracheides, 
and appear to be without pits. In some places there is a direct relation to 
the medullary rays; in one case a vertical strand extends from one ray to 
another, and appears to cross a third ray on the way. It may be asked 
whether the parenchyma may not be traumatic ; there is apparent evidence 
of injury in the outer tissues of the stem, for at one place a layer of periderm 
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