XXXVII] DIELLIA 27 



small stems the column of pith is small : but the Lindsaya-condhion was 

 not seen in any adult stem, though doubtless it occurs in the sporeling. The 

 leaf-trace comes off as two equal straps: but these do not preserve their 

 identity far, and sometimes they unite within the cortex of the stem. As 

 they pursue their course upwards they become moulded in varying degree 

 into a vascular tract of the type well known in the petioles oi AspleJihim and 

 Scolopendrium (Fig. 596). But the outline is not uniform : sometimes the 

 junction is effected by the abaxial margins, sometimes by the middle region 

 of each tract. The latter is reminiscent of Aspleniuin or Scolopeiidrinin 

 (Vol. I, Fig. 157), the former of that of Plagiogyria sernicordata (Studies I, 

 Text-fig. 2). It may involve the peripheral vascular tissues only, while the 

 xylem-tracts remain free: or the fusion may be complete. The absence of 



Fig. 596. Petiolar meristele of Diellia fakata, resulting 

 from fusion of two separate vascular straps of the leaf- 

 trace. The adaxial side is here directed upwards. The 

 xylem-tracts {xy) are here separate, though they sometimes 

 fuse. ////= phloem, / = pericycle enlarged. 



precision in these fusions suggests that they follow upon a compacting of 

 the blade from a more divided state. If that be so, then such fusions may be 

 regarded as homoplastic iri leaves subject to integration of the blade, rather 

 than as giving any trustworthy basis for phyletic comparison. The pinna- 

 traces are marginal in origin. 



The fertile pinna of D. fakata shows a coarse reticulation of the veins 

 (Fig- 597)- The sori are distinctly intra-marginal, with the upper indusial lip 

 assimilated to the surface of the blade, the lower membranous, with adherent 

 margin. Sometimes the single sorus may be distal and solitary on a vein : 

 but there are frequent signs of lateral fusion to form coenosori, with vascular 

 commissures: the structure might accord equally with upgrade fusion or with 

 downgrade disintegration of a coenosorus, but the former is the more probable 

 interpretation (Fig. 597, B, C). The sporangium has' a long stalk, composed 

 in its basal part of only one row of cells. The annulus shows slight traces of 

 obliquity, and has about 20 indurated cells, and a lateral stomium. The 

 number of spores in each sporangium appears to be 48 to 64: they are oval 

 with a prickly reticulate wall. 



