of Coal-Measure Plants. 



283 



There are five primary mesarch bundles in which, as usual, 

 the centripedal xylem is more developed than the centrifugal. 



Figure I. Lyginodendron Oldhamium (Binney). Transverse section of the stem 

 x h\. Photo, by Tarns, Cambridge. 



The broad ring of secondary wood has a diameter of 2'5 — 3 mm., 

 with about 30 elements in the ray. The tissue of the medullary 

 rays has largely perished. External to the secondary wood, traces 

 of a cambium, and of phloem, may here and there be found. 

 The pericycle and inner cortex are badly preserved. 



There are five cortical leaf-traces, .three of which have divided, 

 or begun to divide. Another, to which reference will be made in 

 the next slide, is seen passing through the external margin of the 

 wood. It still retains much of its secondary wood. Some tan- 

 gential elongation of the parenchyma of the pericycle has taken 

 place, for where the trace has divided, the two parts are separated. 

 The pericycle is remarkable as containing unusually large groups 

 of sclerotic nests. 



The outer cortex has the usual dictyoxyloid structure, but 

 much of the thin-walled tissue has disappeared, and secondary 

 crystallisation taken place. The sclerenchymatous strands con- 



21—2 



