MEDULLOSEAE 429 



the common objects of the calcareous nodules. Speci- 

 mens have since been found in other localities, and it 

 is interesting that at Shore Littleburgh they occur in 

 the roof-nodules, which usually show a distinct Flora 

 from that of the nodules in the seam below. 1 



The stems are of rather large size, having a mean 

 diameter of 7 or 8 cm., in the specimens at present 

 known. This dimension includes the leaf-bases, which 

 were adherent to the stem for a long distance before 

 becoming free ; in fact, practically the whole external 

 surface was formed by these leaf- bases, which were 

 spirally arranged, the phyllotaxis, where it could be 

 determined, having followed the | arrangement. Fig. 

 163 will give an idea of the external appearance 

 of the fossil stem ; the surface of the large adherent 

 leaf-bases is marked by a longitudinal striation, due to 

 the hypodermal ribs of sclerenchyma, which stand out 

 prominently in the fossil, though during life they must 

 have been nearly or quite concealed from view by 

 overlying tissue. The transverse section, represented 

 somewhat diagrammatically in Fig. 1 64, shows the chief 

 points in the organisation of the stem. This section 

 was cut near the bottom of a piece of stem about a 

 foot long. At this level, three large leaf- bases are 

 shown ; that marked c in the figure is the nearest to 

 its separation from the stem, and actually became free 

 an inch or two higher up. The next leaf to become 

 free is that marked b, while a remains in connection 

 with the stem for a vertical distance of 5 or 6 inches. At 



1 Mr. Arber described in 1903 a specimen in the Binney Collection at 

 Cambridge. This must have been discovered many years before the type- 

 specimens, but had apparently lain unnoticed. See Arber, " On the Roots 

 of Medullosa anglica," Ann. of Bot. vol. xvii. 1903. 



