43° 



STUDIES IN FOSSIL BOTANY 



higher levels, two new leaf-bases make their appearance, 

 the first (be) between b and c, and the next (ab) between 

 a and b. Thus the order of insertion of the leaves 

 from below upwards was c, b, a, be, ab, an arrangement 

 which implies a f phyllotaxis. The habit of the stem, 



Ssmfc, 



if \ 



1 



Fig. 163. — Mcdullosa auglica. External view of stem, showing two large leaf-bases, 

 with a furrow between them. The surface is ribbed, owing to the presence of 

 hypodermal strands of sclerenchyma. \ nat. size. S. Coll. (G. T. G.) 



clothed with its large adherent leaf- stalks, may well 

 have resembled that of some of the Tree-ferns. 



Coming now to the internal structure of the stem, 

 we find that its organisation resembles that of the 

 majority of the Ferns, in being of the so-called polystelie 

 type. 1 The number of the steles in M. anglica is 



1 I have adhered to the now familiar terms "polystely" and "polystelie," 

 but they are used in a purely descriptive sense without any implication 

 that each of the several steles is to be regarded as homologous with the 

 single stele of a typical monostelic stem. 



