230 



LYCOPODIALES 



[CH. 



secondary scalariform tracheae. The preservation of the tissues 

 abutting on the edge of the wood is usually very imperfect, and 

 the middle cortex of lacunar parenchyma has practically in every 

 case eluded the action of mineralising agents ; the outer cortex, 

 on the other hand, consists of more resistant elements and is 

 frequently well preserved. As in Lepidodendron and Sigillaria 

 stems, meristematic activity produced a broad band of secondary 

 cortex ; and beyond this were attached to cushion-like pads the 

 numerous appendages, each supplied with a single vascular 

 bundle which arose from the primary xylem and passed out- 

 wards through a medullary ray. There is abundant evidence 

 that the appendages were hollow, a fact in striking accord with 

 the aquatic and semi-aquatic habitat (cf Isoetes root, fig. 133, G). 



Fig. 206. Cyperus papyrus. Piece of rhizome showing rootlet-sears. Nat. size. 

 M.S. 



The piece of dried rhizome of Cyperus papyrus shown in fig. 

 206 is an almost exact counterpart of Stigmaria ficoides ; the 

 wrinkled and shrivelled surface and the circular root-scars 

 containing the remains of a vascular bundle are striking 

 features in common and, it may be added, the two plants, though 

 very different in structure and in systematic position, illustrate 

 anatomical adaptations to a similar environment. 



