384 SECTIONAL TRANSACTIONS.— K. 



plants. Here the ovules were borne in two rows near the midrib of the structure. It 

 is quite possible that the megasporophyll of Caytonia will supply the clue to the 

 morphology of the carpel of Aquilegia and other forms of a similar structure. 



Dr. A. B. Rendle, F.R.S., Dr. T. W. Woodhead, Mr. J. Parkin, 

 Dr. E. J. Salisbury, Dr. D. H. Scott, F.R.S. ; Prof. J. M. McLean 

 Thompson. 



Dr. J. B. Lotsy. — Demonstration (during the above Discussion) of 

 Natural Hybrids between Plants and between Human Races in New 

 Zealand and South Africa. 



Prof. F. 0. Bower, F.R.S. — Evolutionary Changes in the Superficial Sorus. 



In certain ferns the sorus took a superficial position in Palaeozoic time, e.g. 

 Oligocarpia and Ptychocarpus. Living examples are seen in Oleichenia, Alsophila, 

 Woodsia and Matteuccia. Originally the sori were all radial and simple. Transitions 

 followed to the gradate and mixed types, and the origin of a basal indusium accom- 

 panied them ; the result is seen in Woodsia, Diacalpe and Pe.rane.ma. The further 

 step to zygomorphy of the sorus in relation to the leaf-margin was taken by Peranema ; 

 this eventuated in the soral type of Dryopteris. The similarity of this to Lindsaya 

 and Nephrolepis was of homoplastic origin ; they are essentially marginal types of 

 Dicksonioid origin. 



Dryopterid derivatives are seen in Polystichum and Polybotrya. A particular 

 interest attaches to the elongated sori of Didymochlcena, Fadyenia and Mesochlcena, 

 for these give the clue to the origin of the sori of Athyrium, Diplazium and Asplenium, 

 which may be held as Dryopteroid derivatives, their indusia representing the remnants 

 of the basal indusium of the Dryopteroid type. 



Matteuccia and Onoclea are also superficial types, of which the former may be 

 still non-indusiate. By fusion of such naked sori in linear series the ccenosori of the 

 Blechnum type originated, covered in by the leaf-margin. These also show the 

 transition from the gradate to the mixed state, together with the innovation of a- 

 photosynthetic ' flange.' By convolution and interruption of the ccenosorus upon a 

 widening leaf -surf ace, as seen in Blechnum punctulatum var. Krebsii, and in Camptosorus 

 sibirica, the condition is arrived at of Phyllitis scolopendriurn (the Hart's Tongue). 



Asplenium and Phyllitis (Scolopendriurn) have usually been classed together ; 

 but if these comparisons be valid their soral similarities are homoplastic. In particular 

 the protective flaps would not be homogenetic but homoplastic. The indusium of 

 Asplenium would represent part of the Dryopteroid indusium ; it would, in fact, be 

 of true indusial character by descent. But the so-called indusium of the Hart's 

 Tongue would be by descent an isolated portion of the original margin of the leaf- 

 blade, which already in Blechnum has assumed an ' indusoid ' character. 



Prof. T. Johnson. — Irish Fossil Gymnosperms. (Communicated in title 

 only. ) 



While Ireland now possesses only two indigenous conifers — Juniperus and Taxus — 

 it was in the early Tertiary relatively rich. Though a scientific survey of the timbers 

 found in the bogs has never been made, Pinus sylveslris is not uncommon, and 

 P. montana var. Mughus is recorded. The writer has had the opportunity of 

 examining the fossil plants collected by Bailey, Gardner and others in Co. Antrim, 

 and those found in the core of the bore at Washing Bay, Co. Tyrone, in 1916, 

 carried out by the Board of Trade in the search for coal. The paper deals with 

 Oingko, Taxus, Podocarpus, Pinus, Sequoia, Cryptomeria, Cunninghamia, Gupressus, 

 Libocedrus and Ephedra. 



The deposits are regarded as Oligocene, with connection with those of Mull in 

 Scotland, the plants showing affinities with the flora of East Asia, Pacific North 

 America and the Mediterranean region. Cunninghamia, now confined to East Asia, 

 is the most interesting addition. 



