XXIX] HBTERANGIUM 77 



its outer boundary at f in fig. 41 1, A. Beyond the pericycle 

 is the broad parenchymatous cortex with leaf-traces, It, and 

 some sclerenchymatous patches, s. The vascular strand a is 

 passing into the base of a leaf-stalk. In the stem shown in fig. 

 411, B, 1-4 cm. X 7 mm., a decurrent petiole is seen at the upper 

 end with its single vascular strand, a, and two sclerous nests; 

 a similar though detached leaf-base occurs at the opposite end of 

 the long diameter. Other leaf-traces are seen at b and c. From 

 the left-hand side of the stele a curved strand of tracheids is 

 passing out to supply a root, r. 



ii. Root. 



Adventitious roots of endogenous origin are occasionally met 

 with in Heterangium stems, but we have less information as to 

 their anatomy than in the case of Lyginopteris. In a specimen of 

 Heterangium Lomaxi figured by Williamson and Scott^ three roots 

 are seen in a vertical series growing outwards through the cortex 

 of a stem. The roots agree generally with those of Lyginopteris 

 but the outermost cortical layers possess no special features. 



iii. Leaf. 



The large compound fronds long known as Sphenopteris elegans 

 were recognised by Kidston as the leaves of Heterangium by the 

 closely arranged transverse striae or narrow ribs on the rachis 

 and pinnae which are the expression on the carbonised impressions 

 of the horizontal plates of sclerous tissue in the petrified stems 

 and petioles of Heterangium. The dichotomously branched fronds 

 are included by Stur in his genus Diplotmema and that author 

 figures several typical examples in his ' Culm Flora '^. Fig. 413, A, 

 shows a forked axis with the bases of more slender branches and 

 the characteristic transverse bands and in fig. 413, B part of a pinna 

 is reproduced. In general appearance, except in the bifurcating 

 pinnae, the fronds resemble those of Davallia tenuifolia with 

 which Brongniart compared the Palaeozoic species. There is 

 Uttle doubt that Sphenopteris dissecta and some other species 

 were also borne on Heterangium stems. The rachis and petioles 



1 Williamson and Scott (95) PI. xxvn. fig. 28. 



2 Stur (77) p. 236, Pis. xm. xiv. 



