TRANSACTIONS OF SECTION K. 569 



crescentic in section, instead of being approximately triangular as figured in 

 Williamson's and Stenzel's plants. A similar crescentic trace occurs, however, 

 in some of Williamson's sections of the specimens described in 1888. The evi- 

 dence of the new specimen is distinctly in favour of the view that the large 

 strand given off from the stele is really a leaf-trace and not itself a branch. 

 The branch which the leaf-trace gives off higher up may thus retain the name 

 of axillary shoot, originally bestowed upon it by Stenzel. 



The origin of the peripheral loops and the continuity of the protoxylem of 

 the leaf -trace with that of the stele can be followed in the serial sections. 



The course of the aphlebia-strands, which are given off by the leaf-traces 

 both before and after their separation from the stele, can also be followed. 



The author inclines to the view that the Z. Grayi type of stele represents an 

 elaborated protostele, rather than a condensation of a more complex vascular 

 system. On the other hand, the relation to the stem of Diplolabis Bbmeri, 

 described by Mr. Gordon, would be a collateral one rather than a direct filiation. 



4. Recent Researches on the Jurassic Plants of Yorkshire. 

 By H. Hamshaw Thomas, M.A. 



Since the formation of the large collections of fossils from the Yorkshire coast 

 by Williamson, Bean, Leckenby, and other enthusiastic collectors, few plant- 

 remains of importance have been obtained from this famous locality. In 1879 

 Professor Nathorst, of Stockholm, had obtained a number of new and interesting 

 forms, and during a visit in 1909 he made further important discoveries, on 

 which the first of his recent papers on Williamsonia was based. It became clear 

 that much further information about the flora of Jurassic times might be 

 obtained by renewed researches in Yorkshire, and the present paper is a brief 

 summary of some of the results obtained by Professor Nathorst, Dr. T. G. Halle, 

 and myself. 



Important additions to our knowledge of the Bennettitales have been made by 

 Professor Nathorst. He distinguished, for the first time, the male sporophylls 

 of Williamsonia, which are united together into a cup-like structure somewhat 

 comparable with a flower. The sporophylls are more or less covered with large 

 sessile synangia from which the remains of the microspores can be extracted in 

 great numbers by treatment with acid in the usual way. Williamsonia appears 

 to have been unlike most of the Bennettites (or Cycadeoidea) in having unisexual 

 ' flowers.' Several species of male ' flowers ' have been distinguished, which differ 

 in the number and the arrangement of the synangia. In »ome forms a con- 

 siderable reduction in the number of synangia seems to have taken place. The 

 female strobilus of Williamsonia bears a close resemblance to the corresponding 

 structure in Bennettites. 



1 have recently discovered near Gristhorpe a new Bennettitalian ' flower ' 

 which appears to be bisexual. The central axis bore the usual ovules and inter- 

 seminal scales, and below this there was a whorl of five or six large free sporo- 

 phylls, arranged in a similar way to the petals of a hypogynous flower. On 

 these sporophylls five or six large reniform sporangia were borne. 



Some facts in the history of seed-bearing plants will probably be furnished 

 by the study of some small fruit-like bodies which I have recently found and 

 have named Caytonia. They appear to contain the remains of eight to ten seeds, 

 each 1 to 2 mm. long, and similar isolated seeds have been obtained. A certain 

 amount of their structure has been preserved, and parts of the integuments, 

 nucellus, and micropylar tubes can be made out. 



Some additional information has been obtained about the mesozoic ferns. 

 Dr. Halle has found that the sporangia of some specimens of Cladophlebis denti- 

 culata were pear-shaped and had an apical cap of thickened cells. He suggests 

 the affinity of these with Seftenbergia. I believe that the sporangia of Todites, 

 which are arranged much as in the modern Todea, possessed a similar apical cap 

 of cells, and were in this respect different from the recent forms. 



The sporangia and spores of Goniopteris hymenophylloides have been dis- 

 covered and show resemblances to those of some of the modern Cyathseaceae. 

 Fertile specimens of Cladophlebis lobifolia have been obtained which are some- 

 what similar to recent Dicksonias in the form of the sori and spores. The 



