226 



Dr. D. H. Scott. 



outwards. In M. anglica, where they are so much more numerous, they are 

 quite irregular in form. 



The distinction is not absolute, for in parts of the raehis attributed to 

 M. anglica one may find much the same arrangement as in M. pusilla. 

 Comparing leaf-base with leaf-base, however, there appears to be a real 

 difference between the two plants. The hypoderma of M. pusilla is of the 

 type of Eenault's Myelopteris Landriotii, var. « (Eenault, '75, Plate 5, fig. 41), 

 while that of M. anglica is more like his var. /3 (loc. cit., Plate 4, fig. 29). Of 

 course, the agreement is far from exact, for Eenault's petioles no doubt 

 belonged to quite different species of Medullosa from ours. 



In the leaf-base of M. pusilla there are very few gum-canals visible in the 

 hypoderma, and they are not very numerous altogether (fig. 4). In M. anglica 

 they are very common in the hypoderma, and fairly so elsewhere. This 

 distinction, however, is of very doubtful value, for in a section of a detached 

 petiole or leaf-base probably referable to M. pusilla, gum-canals are numerous 

 in the parenchyma outside the sclerotic strands, most of the strands having 

 canals corresponding to them. This tissue is hardly preserved at all in the 

 type-specimen, so the small number of hypodermal canals observed may be 

 deceptive. Their distribution appears to have been a little different from 

 that in M. anglica, but in that species also the external parenchyma is seldom 

 well preserved, so comparison is difficult. 



Summary and Conclusions. 



If we draw up a diagnosis of M. pusilla on the lines of that given for M. anglica 

 (Scott, '99, p. Ill), we find few distinctions between them, apart from size. 



Medullosa pusilla. — (Scott, ' Studies in Fossil Botany,' second edition, p. 441, 

 1909.) 



Stem clothed by the relatively large decurrent leaf-bases. 



Vascular system of stem consisting of three uniform steles. Star-rings 

 absent. Interior of each stele wholly occupied by primary wood. 



Secondary wood of moderate thickness, most developed on the inner sides 

 of the steles. Tracheides (apart from the protoxylem) with multiseriate 

 bordered pits. 



Leaf-traces probably concentric on leaving the steles, but with little or no 

 secondary wood, branching and becoming collateral as they pass into the 

 leaf-bases. 



Leaf-oases, with a narrow hypoderma, consisting of a single, or locally douhle 

 series of strands, and resembling that of Myelopteris Landriotii, var. « Eenault. 



Gum-canals numerous in the cortex, scattered in the leaf-bases. Stem 

 small, about 2 cm. in diameter, including the leaf-bases. 



