HETERANGIUM 



4°3 



formed by the decurrent bases of the spirally arranged 

 leaf-stalks (Fig. 154). The general character of the 

 foliage is known ; the leaves, like those of Lygino- 

 dendron oldhamium, were highly compound, and are 

 referable to the Sphenopteris type (cf. Fig. 1 60). There 

 is, in fact, good evidence for the identification of Heter- 



FlG. i^.—Hcterangium Grievii. Restoration of a portion of the stem, showing trans- 

 verse and longitudinal section, and part of the external surface, .r, primary wood of 

 stele ; -r 2 , secondary wood ; pc, phloem and pericycle (left blank) ; c, cortex, with 

 horizontal sclerotic bands ; liy, hypoderma of stem and petiole; l.t, leaf-traces, one 

 of which is entering the petiole ; r, adventitious root. The bases of several petioles 

 are shown. Enlarged. After Williamson, Phil. Trans. 



angium Grievii with a definite species of Sphenopteris, 

 but before entering into this question it will be necessary 

 to describe the organisation of the specimens with 

 structure preserved. 



1. The Stem (H. Grievii). — The stem of Heteran- 

 gium, like that of Lyginodendron, had a single vascular 



27 



