ee 
five 
parenchymatous core. “‘Steles,”” including the surround- 
steles’” arranged concentrically around a central 
ing secondary wood, elliptical in outline in’ transverse 
section, and varying from one to three cm. along the long 
axis. Secondary xylem forming a concentric cylinder 
wround each ‘‘stele.’” but, to a moderate degree, endo- 
centrically developed. ‘‘Star rings”” and accessory inter- 
nal bundles absent. Primary wood arranged in small 
uggregates, or scattered bundles surrounded by paren- 
chyma. Secondary wood consists of tracheids and rays. 
Tracheids large, with closely spaced circular bordered pits 
on the radial walls. Rays very abundant and of two 
types: uniseriate and multiseriate, the latter four to six 
cells in width. The rays flare conspicuously in the phloem. 
Locality and horizon: Lower Permian, Moran Formation, Section 
754, Texan Emigration and Land Company Survey, 10 miles west of 
Newcastle, Young County, Texas. 
Collected by: Eleanor L. Olsen. 
Material: Seven silicified stem fragments. 
Type: Seven stem fragments and 7 ground sections in the Paleo- 
botanical Collections of Harvard University, No. 50,001 to 50,007. 
Discussion 
The specimens under consideration clearly conform to 
the definition of the genus Medul/osa in possessing ‘‘poly- 
stelic’” structure, with each stelar component developing, 
independently, its own cylinder of secondary tissues. 
The known members of the genus may be divided into 
three geographic and stratigraphic categories: 1) species 
of the Kuropean (German) Permian: 2) species of the 
Kuropean Carboniferous; and 8) species of the American 
Carboniferous (chiefly mid-Pennsylvanian /). 
Comparison of the stelar patterns and stem structure 
of the Kuropean Permian forms (Plate ILNTT, figs. 8 to 
11) with JZ. Olseniae rules out any close relationship. Phe 
former are all characterized by elongated and peripherally 
