SECTIONAL TRANSACTIONS— K. 429 



dorsiventral species. The rhizophores of the latter type have been the 

 subject of much discussion and it has been concluded on general morpho- 

 logical grounds that they are organs sui generis ; experimental evidence 

 has tended to show that they, and particularly the angle-meristems from 

 which they arise, are indifferent structures capable either of forming roots 

 or of being converted into leafy shoots. The organisation of the stock of 

 Isoetes has also been repeatedly discussed. The rhizophoric region consists 

 of the basal part of the stock which possesses two or three stelar lobes with 

 a line of meristem running along the lower edges of these. 



These anomalous rooting systems are of particular interest for com- 

 parison with those of the fossil Lycopodiales. 



Prof. J. Walton. — The morphology of the rhizophoric parts of the extinct 



Lycopods (2.55). 



Fairly close comparisons based on external features may be made between 

 the root-bearing stocks of Stigmaria, Pleuromeia, Nathorstiana and Isoetes. 

 There are structural peculiarities at the base of the aerial stem of Lepido- 

 phloios wunschianus Carr. and Lepidodendron saalfeldense Solms which 

 suggest further comparisons with Isoetes. In Selaginella spinulosa the basal 

 knot may be compared with the rhizophoric parts of Stigmaria and Isoetes, 

 but no corresponding structure is found elsewhere in the living Lycopods. 

 There is nothing comparable to the rhizophore of Selaginella (excluding 

 S. spinulosa) in the fossil Lycopods. 



Prof. T. M. Harris. — Naiadita, a strange fossil Bryophyte (3.15). 



Naiadita lanceolata is a very common fossil in the English Rhaetic and has 

 been recognised as a zone fossil for ninety years. It consists of a slender 

 parenchymatous axis bearing unicellular rhizoids and lanceolate leaves, 

 arranged in a | spiral. The leaves have a well-marked apical cell but no 

 midrib. The axis usually terminates in a conical gemma cup ; the gemmae 

 are multicellular and germinate directly (i.e. without a protonema stage). 

 The antheridia are still undiscovered. The archegonia are borne laterally 

 and are at first sessile and naked but afterwards a perianth of about four 

 leaves grows round them and the whole is carried up by a pedicel. The 

 sporophyte consists of a spherical capsule and a small hemispherical foot 

 embedded in the pedicel : there is no seta. The capsule is cleistocarpic ; 

 its wall is composed of a single layer of evenly and thickened square cells. 

 The capsule has no columella nor elaters but only spore tetrads. There 

 is some evidence that Naiadita was a submerged water-plant. 



All organs of Naiadita are typically bryophytic, but its further classification 

 is only possible if some considerable general assumptions about Bryophyte 

 morphology are made. On Wettstein's view of gametophyte reduction, for 

 example, Naiadita could be regarded as one of the Sphaerocarpales and 

 closely related to Riella. 



Miss A. Bennett. — The ecology of the limestone pavements at Hutton Roof 

 and Tarleton (3.35). 



The vegetation of the limestone areas depends largely upon the con- 

 figuration of the ground and falls into three main groups : (i) Pavements; 

 (2) Escarpments; (3) Screes. The associations developed are regulated by 

 exposure to weather conditions and the angle of slope, which together 

 control accumulation of soil and pY\ value. Grazing by animals causes 



