XXIX] LYGINOPTERIS 69 



superficial tissue forms a striking feature by which a Lyginopteris 

 root may often be recognised at a glance. The root represented 

 in fig. 410, approximately 2 mm. in diameter, has a heptarch 

 stele divided into seven xylem-groups by crushed bands of 

 parenchyma and a protoxylem strand occupies the apex of each 

 projecting angle (fig. 410, px). The superficial cylinder of clear 

 cells is seen at a. A very small root is seen at r in fig. 410. 



a 



r 



FIG. 410. Lyginopteris oldhamia, young root, x 30. (Kidston Coll. 403.) 



Fig. 415, C, represents part of an older root in which the pent- 

 arch primary xylem is enclosed by broad wedge-like groups of 

 secondary xylem and phloem separated by conspicuous medullary 

 rays opposite the protoxylem strands (px). Crushed primary 

 phloem arcs, p, are often clearly recognisable beyond the cambium. 

 The secondary thickening, as Williamson and Scott state, 'takes 

 place exactly in the manner typical of roots of Dicotyledons, 

 so that this fossil might very well be used for purposes of demon- 

 stration as illustrating the secondary growth of a root with 

 diagrammatic clearness' 1 . The young roots of Lyginopteris 

 resemble in many respects those of Marattiaceous Ferns, though 

 the presence of a single apical cell, if such occurs, is a distinguishing 



1 Williamson and Scott (95) p. 739. 



