lo Watson, On the Ulodoidi-oid Scar. 



decay away, and it is easy to see how the vascular CN'h'nder 

 of the branch might be torn out, leaving- a hole in the 

 centre. 



U'hen fossilised, this lax^er of periderm would be con- 

 verted into coal, forming a film over the area of the scar, 

 and the hole in the centre would be alone left uncovered. 



The 3rd specimen, also figured by Mr. Kidston, shews 

 the place where a Ulodendroid scar should be covered 

 with moderately well preserved leaf-bases. These leaf- 

 bases are arranged in the same series as those on the 

 ordinary surface of the stem in the lower part of the scar, 

 but it must be very distinctly noticed that in the upper 

 part they do not at all fit into the ordinary stem series. 

 It should also be noticed that this scar is raised above 

 the general surface of the stem. 



I explain the appearance shewn on this scar as being 

 due to a small bit of the leaf-scar-bearing cortex of the 

 branch being left attached to the lower part of the edge 

 of the scar, and being folded over and crushed down on 

 to the area of the scar. This explanation it seems to me 

 is adequate to explain the fact that the leaf-scars on the 

 scar surface are in the same series as the stem leaf-bases 

 at the lower part of the scar, but do not fit at the top. 



Summary. 



It is pointed out that there is a good deal of evidence 

 tending to discredit the ordinary theory of the method of 

 formation and significance of the Ulodendroid scar, in 

 that it is produced by the pressure of the base of a sessile 

 cone. 



It is suggested that the Ulodendroid scar merely 

 represents the place of insertion of an ordinary branch, 

 which was probably provided with some sort of branch- 

 shedding mechanism. 



A specimen is brought forward which is interpreted. 



