Knowledge of Lyginodendron. 67 
we cannot absolutely prove their identity with Lyginodendron V 
On page 742 of the same work we find the following account 
of the large Oldham fossil : — 
£ There remains the large specimen showing structure, 
received from Mr. Nield, and referred to in Memoir IV. p. 386. 
The specimen includes the pith and a portion of the wide 
zone of secondary wood. Sections in the three directions 
have been cut and clearly exhibit the structure so far as it is 
preserved. The diameter of the pith is 3*3 x 2*3 cm. The 
maximum radial thickness of the secondary wood is 5*8 cm., 
but we cannot be certain that its whole thickness is preserved. 
Assuming, however, that we have the whole thickness of the 
wood, the radius of the stem up to the cambium would have 
been over 7 cm., and its diameter over 14 cm. We cannot 
tell what was the diameter of the whole stem, for we know 
nothing of the cortex. No authentic ..specimen of Lygino- 
dendron which we have seen, however, has secondary wood 
of a greater thickness than about 6 mm. ; so, if we judge by 
this dimension, the stem in question must have been nearly 
ten times as large as that of any undoubted Lyginodendron 
in the Williamson Collection. Unfortunately, the only 
structure preserved is that of the secondary wood. Its general 
anatomy is identical with that of certain specimens of Lygino- 
dendron. The tracheids are smaller than is usual in Lygino- 
dendron , but not smaller than in some undoubted stems of 
that plant. The radial section shows the muriform rays 
and the pits on the walls of the tracheids, which, in so far 
as their preservation allows of comparison, agree very well 
with those of our plant. The pith is completely disorganized, 
and no trace of the primary wood can be recognized. There 
is, however, a narrow incomplete zone of internal secondary 
wood, distinct from the rest, at the margin of the pith, which 
recalls the anomalous medullary tissue sometimes found in 
Lyginodendron . Although the parenchyma of the pith has 
perished, the cavity contains clusters of dark brown cells, 
Phil. Trans., Vol. 186 (1895) B, pp. 705, 706. 
F 2 
