SIGILLARIA 



229 



Coal-measure nodules. In S. mamillaris (see Fig. 87) 

 the structure is almost identical with that of the Favu- 

 larian 5. elegans ; in 5. scutettata the crenulations of the 

 primary wood are comparatively slight (Fig. 94). On 

 the whole the wood structure in both is the same as 



Fig. 94. — Sigillaria scutellata. — Transverse section of a portion of the wood, showing 

 primary xylemSbelow and secondary xylem above. The protoxylem-groups lie at 

 the outer border of the primary xylem. X about 50. From a photograph lent 

 by Mr. E. A. Newell Arber, F.G.S. S. Coll. 2300. 



that above described. Arber and Thomas find that in 

 5. scutellata the periderm was formed on the inner side 

 of a meristematic zone which was active periodically. 

 The ribs consist largely of the phelloderm, but were 

 probably already present in the primary condition of 

 the stem. The authors were able to demonstrate the 

 presence of a ligule and ligular pit on the leaf-base. 



