332 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1918. 



narrow ribs without leaf scars are developed. The forms are some- 

 times set apart under the name Polleriana, and when transverse fur- 

 rows appeal-, the forms are grouped under the name Tasselata. 



The various stages of preservation yield characteristic surface 

 features thought to indicate distinct genera by the older students 

 but useful now as descriptive terms. Thus when partially decorti- 

 cated, the inwardly enlarging strands of aerochyma result in vertical 

 rows of pairs of large mammilae, and such stems have been called 

 Syringodeudron. Petrified material of Sigillaria is rarely found. The 



o 

 o 



o 

 o 

 o 

 o 



o 

 o 



o 

 o 

 o 

 o 

 olo 



kUM 



o 

 o 

 o 

 o 

 o 

 o 

 o 



Fig. 13.— Types of Sigillaria stem ornamentation (diagrammatic). 



A. Leiodermana\_ , 



t. ™ .l >Subsigil anae. 



B. Clathrana > b 



C Tasselata 



D. Ithytidolepis| 



E. Polleria.ia 



F. Favularia 



Eusigillariao. 



pith was very large and the vascular cylinder thin and sometimes 

 broken up into separate bundles. Tracheids were reticulate or 

 scalariform, increasing in size centripetally. Secondary wood con- 

 sists of radically arranged scalariform and pitted tracheids, cen- 

 trifugal in development with narrow medullary rays. Cortex was 

 thick with an inner soft zone and an outer mechanical zone as in 

 Lepidodendraceae. The leaf traces had an inner centripetal pri- 

 mary strand surrounded by a centrifugal secondary zone. The 

 leaves are much like those of Lepidodendron with a central con- 

 centric vascular strand surrounded by a considerable development 

 of transfusion tissue. In some instances the strand is double. The 



