Knowledge of Lyginodendron. 81 
we have an irregular network of tracheids with the large 
meshes occupied by groups of polygonal parenchymatous 
cells. The tangentially- cut medullary rays assume the form 
of oval, circular, or oblong groups of cells, bounded by the 
extremely sinuous and contorted tracheids. The chief dif- 
ference between the tangential section of Lyginodendron 
anomalum and Lyginodendron robustum consists in the 
broader and shorter medullary rays of the former, and the 
more irregular and sinuous course of the tracheids. In a 
section through the centrifugal wood of Lyginodendron ro- 
bustum in the neighbourhood of an outgoing leaf-trace, the 
tracheids are similarly contorted to those in Lyginodendron 
anomalum. In a tranverse section of the former passing 
through a leaf-trace-bundle, as shown in PI. V, Fig. 6 , t and 
t\ and PI. VI, Fig. 15, the broad distal end of the trace is 
followed by long and narrow parenchymatous cells, which 
have accompanied the tracheids from the inner edge of the 
wood. The general appearance of such a section is almost 
identical with that of a transverse section of Lyginodendron 
anomalum. Such a comparison suggests the possibility that 
the shorter and broader medullary rays and the more 
irregular course of the tracheids may not represent the 
normal character of the stem from which the Arran frag- 
ment was obtained, but that these appearances may be the 
result of some disturbing influence in the secondary wood. 
The resemblance between Lyginodendron robustum and 
Lyginodendron anomalum as regards the structure of the 
wood and the form of the medullary rays, which is specially 
striking in the wood of the former species where the normal 
form of the rays is modified by the bending of the tracheids 
to a leaf-trace-bundle, points to the possibility of the two 
forms being closely allied to one another. The Arran frag- 
ment is much too small to allow of precise identification, 
but the structure of the wood renders it extremely probable 
that in Lyginodendron anomalum , Will., we have a small piece 
of a stem which possessed secondary wood of the cyca- 
dean type very similar in structure to that of Lygmodendron 
G 
