68 PTERIDOSPEEMEAE [CH. 



The roots of Lyginopteris arise on all sides of the radially sym- 

 metrical stem in the pericycle region ; they are copiously branched 

 as is shown by the abundance of roots of various sizes in close 

 association. No roots have been discovered exceeding 1 cm. in 

 diameter nor have any been recorded with secondary periderm- 

 tissue. The absence of root-hairs and the more or less lacunar 

 structure of the cortex are indicative of swampy ground. It 

 is seldom that the palaeobotanist has an opportunity of investi- 

 gating the growing-points of Palaeozoic plants, and for this reason 

 some well-preserved apices of Lyginopteris roots, attributed to 

 that genus on the ground of constant association with fragments 

 of stems in the calcareous nodules of Dulesgate, are of special 

 interest. One of these specimens was figured by Dr Stopes and 

 Mr Watson 1 in their account of plant-bearing nodules, and a de- 

 scription of that and other examples has since been published by 

 Prof. Weiss 2 . A longitudinal section of a root-tip, -21 mm. in 

 diameter at its broadest part, shows a root-cap which suggests 

 an origin from a single cell, but an examination of the plerome- 

 cylinder in a slightly tangential section does not afford conclusive 

 evidence of the occurrence of a single initial cell. Weiss on the 

 whole inclines to the view that Lyginopteris possessed a single 

 apical cell like the roots of Leptosporangiate Ferns, though he 

 prefers to leave the decision open. Attention is drawn to the 

 fact that the plate of tracheidal tissue in emerging lateral rootlets 

 is vertical as in Phanerogams and not horizontal as in recent 

 Pteridophyta. 



The vascular tissue of a Lyginopteris root (fig. 410) consists 

 of from three to eight alternate strands of centripetal xylem 

 and phloem, and with the metaxylem is associated a small amount 

 of conjunctive parenchyma which does not form a central pith. 

 The pericycle, one to several layers broad, is succeeded by an 

 endodermis which occasionally shows the characteristic thickenings 

 on the radial walls. A broad cortex of thin-walled lacunar tissue 

 with numerous secretory cells is bounded externally by a super- 

 ficial cylinder of two or more layers of comparatively large and 

 thin cells, the outermost of which are radially elongated. This 



1 Slopes and Watson (08) PI. xvn. fig. 1. 



2 Weiss, F. E. (13). 



