72 LYCOPODIALES [CH. 



In some specimens of Pleuromeia the upper portion is 

 clothed with crowded and imbricate sporophylls which reach a 

 length of 2'5 cm., a maximum breadth of 27 cm., and a thickness 

 of 1 mm. Each sporophyll has a thin wing-like border, and 

 on the lower face are several parallel lines. Solms-Laubach 

 describes the sporangium or ovule as attached to the lower 

 surface of the sporophyll and this opinion has been confirmed by 

 Fitting^ who has also brought forward satisfactory evidence in 

 favour of the sporangial nature of the reproductive organs. 

 Fitting found numerous spores in the Bunter Sandstone near 

 Halle ; these are flattened circular bodies 0'5 — 0'7 mm. in dia- 

 meter with a granulated surface and the three converging lines 

 characteristic of spores produced in tetrads. The .comparison 

 made by this author between 'the sporophylls of Pleuromeia, 

 which bore the sporangia on the lower surface instead of on the 

 upper as in other lycopodiaceous plants, and the pollen-sacs of 

 Conifers, is worthy of note in reference to the possible relation- 

 ship between Conifers and Lycopods. 



A comparison of the Isoetes stem represented in fig. 132, A, 

 with the base of a Pleuromeia shows a striking similarity, but, 

 as Fitting points out, the Stigmaria-like arms of the fossil con- 

 tained a vascular cylinder whereas the blunt lobes of Isoetes 

 consist exclusively of cortical tissue, the roots being given off 

 from the grooves between the lobes of the tuberous stem. 



The position of Pleurom,eia must for the present be left an 

 open question ; it is, however, clear that the plant bears a close 

 resemblance in the form of its base to the Stigmarian branches 

 of Lepidodendron and Sigillaria. The vegetative shoot appears 

 to be constructed on a plan similar to that of these two 

 Palaeozoic genera, but the strobilus is of a different type. It 

 would seem probable that Pleuromeia may be closely allied to 

 Isoetes and to the arborescent Lycopods of Palaeozoic floras. 

 It is not improbably a link in a chain of types which includes 

 Sigillaria on the one hand and Isoetes on the other. 



It is not improbable that a specimen from the Lower 

 Bunter of Commern which Blanckenhorn made the type of a 

 new species, Sigillaria oculina (fig. 134, B) is specifically 



1 Fitting (07). 



