<?/ Ulodendron to Lepidodendron, dsc. 247 



with Knorria acicularis that I have no hesitation in referring 

 that fossil to this species. 



The explanation of how Knorria is formed will be learnt 

 from an examination of the internal structure of Lepidoden- 

 dron. As far as the present example of Knorria acicularis is 

 concerned, the more delicate tissue surrounding the central 

 vascular bundle appears to have decayed, and the bundle thus 

 freed has probably floated out of the cortical cylinder, which 

 subsequently became filled with sediment. Pressure now 

 acting on the cortical cylinder has forced the mud which filled 

 its interior up the small channels through which the foliar 

 vascular bundles passed to the leaves ; the bark next appears 

 to have decayed, leaving the impression of its outer sur- 

 face on the surrounding matrix. The preservation of the 

 casts of the vascular-bundle channels has been assisted by 

 the decayed bark remaining around them in the form of a 

 fine powder, and so helping to prevent their obliteration by 

 subsequent pressure or infiltration. In this manner were 

 formed the little acicular points (the casts of the channels 

 through which the foliar vascular bundles passed) which 

 characterize Knorria acicularis^ Goppert. Some specimens 

 of Knorria imhricata appear to be formed by a partial decay 

 of the outer surface of the bark before fossilization took 

 place. 



It is impossible to correlate the various named species of 

 Knorria with the plants to which they really belong, as any 

 species of Lepidodendron might produce one or more 

 species of Knorria, according to the conditions which attended 

 its mineralization *. Lepidopliloios and the Clathrarian 

 Sigillarice might also form Knorria-[\kQ fossils. 



The type of Flemingites pedroanus, Carruthers, is in the 

 collection of the British Museum. I have failed to see any 

 character in which it diifers from Lepidodendron Veltheimi- 

 anum. 



The figure given by Mr. T. Allan of a vegetable impression 

 found in the quarry of Craigleith is a good example of Lepi- 

 dodendron Veltheimianum showing the Ulodendroid scars f. 

 This example was subsequently named Ulodendron Allani 

 by Buckland and Lepidodendron ornatissimum by Brong- 

 niart. Lindley and Hutton mention Allan's figure as syno- 



* There is in my coUectiou a core, wliicli lifts out of an impression of 

 typical Lepidodendron VeU.heimianum, and is identical with the figure of 

 Lepidodendron tetragonnm as given by Geinitz in his * Darstelluno- der 

 Flora des Hainichen-Ehersdorfer und des Flohaer Kohlenbassins,' pi. iii. 

 fig. 2. My example came from the Calciferous-Sandstone series, Water 

 cf Leith, between Slateford and Colinton, Midlothian. 



t Trans. Roy. Soc. Edinb. vol. ix. pi. xiv. 



