III. On williamsoniella , a new type of bennettitalean flower

Abstract

It is now generally recognised that the Benettitales occupied a dominant position in the vegetation during part of the Mesozoic period, and the elucidation of their reproductive structures is therefore of special importance. An additional stimulus has been given to the study of their remains by the suggestion, on the part of some botanists, that in the morphological features of these plants we may find a solution of the problem of the origin of the Angiosperms. The Estuarine beds of North East Yorkshire which had provided some of the earlier specimens had remained for a long time unexplored until the chance discovery of the beautiful Williamsonia spectabilis flower by Prof. Nathorst. Subsequently to Nathorst’s discovery I commenced a systematic examination of the Jurassic plant-beds of, Yorkshire, and Dr. Halle paid a visit to the coast in 1910 which resulted in the discovery of many important specimens. The previously described specimens belonging to the genus Williamsonia were found in the Lower Estuarine beds near Whitby, Runswick and Marske, while other well preserved examples were derived from the Middle Estuarine beds at Cloughton Wyke. The examples now to be described were obtained from the famous Gristhorpe plant-bed, which had not previously—so far as I know—yielded any examples of fertile structures clearly referable to the Bennettitales. The Gristhorpe bed is a layer of bluish-grey shaly clay, 1-3 feet thick, and containing very beautifully preserved plant remains. It is exposed on the shore at the northern end of Gristhorpe Bay, which lies between Scarborough and Filey; it runs up into the cliff (Bed Cliff) towards the north, but is here covered by Boulder Clay and unworkable. About four or five hundred yards farther it descends again and is found on the shore at the extreme southern (or south-eastern) end of Cayton Bay, but soon runs out to sea once more. It would appear that most of the fine specimens collected in former days by Williamson, Bean and other workers from this locality were obtained on the Gristhorpe Bay side, and this may perhaps account for the non-discovery of such recently discovered genera as Williamsoniella, Eretmophyllum and Caytonia We must also remember that coast-erosion is proceeding at a rapid rate in Yorkshire, and that the parts of the bed now exposed may well contain new plants, for in a distance of a few yards the assemblage of forms may change completely. It is unnecessary to describe the strata in which the plant-bed occurs, but it has been shown by Williamson that they belong to the Middle Estuarine Series of the Middle Jurassic.