﻿Explanation of Plat.: LIIl 



Fig. i. Cross-section of a stem of Lyginoptcris oldhamia, about ^/ 2 times 

 the natural size. At the margin of the large central pith area, 

 which contains numerous sclerotic nests, are the primary wood 

 strands (.r), eight in number; external to these is the broad 

 zone of secondary wood (with cambium and secondary phloem), 

 interrupted by the passage of the leaf traces ; ph, a primary phloem 

 group ; pd, periderm, limiting the pericycle which contains other 

 sclerotic groups; It i-lt 5, leaf traces (numbered in the order of 

 their phyllotaxy) becoming twined while ascending in the peri- 

 cycle; the periderm is followed by the inner cortex and the outer 

 cortex, the latter with its radial plates, the longitudinal anasto- 

 moses of which are not seen in the cross-section. From the 

 Lower Coal Measures at Oldham. After Williamson and Scott. 



Fig. 2. Fragment, in natural size, from a portion of the frond of Sphenop- 

 tcris Hoeninghausii, the leaf of Lyginoptcris. From the Pottsville 

 near Quinnimont, West Virginia. 



