242 STUDIES IN FOSSIL BOTANY 



microscopic structure of coal-plants, is to avoid con- 

 fusing these intruders with integral parts of the organs 

 which they invade. We may form some idea of the 

 conditions under which the Stigmariae grew, from the 

 analogy of weeds growing on a leaf-mould heap, and 

 sending their roots in all directions through the decay- 

 ing vegetable mass beneath them ; only, in the case 

 of the Stigmaria, the weeds are represented by gigantic 

 trees. Special care is necessary in the frequent cases 

 where the rootlets led a kind of cannibal existence, 

 burrowing into roots and rootlets of their own kind. 

 Such cases have deceived even practised observers ; thus 

 Goppert described an intruding rootlet, found in the 

 pith of a Stigmarian axis, as part of the structure of 

 the latter, and this elementary blunder misled several 

 of his successors, until Williamson set the matter 

 right. 



2. Anatomical Structure. — We have now to consider 

 the internal structure of Stigmaria and its appendages ; 

 our description will be based in the first place on the 

 common type S.ficoides, which is by far the best known. 



The main axis of Stigmaria consisted of a well- 

 developed vascular cylinder, surrounded by cortex and 

 periderm (see Fig. 98). The centre of the stele was 

 occupied by a fair-sized pith, the tissue of which is 

 rarely found preserved, except in the outer part, 

 next the wood. Possibly the pith may have been 

 fistular during life. The wood forms a broad zone, 

 divided up into bundles by the principal medullary 

 rays (Fig. 98, x). These bundles constantly anasto- 

 mose laterally with each other, forming a network, in 



