MaiicJiestcr Memoirs, Vol. Hi. (1908), No. A. 



IV. "On the Ulodendroid Scar." 



By D. M. S. Watson, B.Sc. 



Kescarcli Student in the Geological Department of the J Ictoria University 

 of Manchester. 



( KeeeiTcd and Read Novc///l>er i3th, igoy. ) 



Certain stems of the genera Sigillaria, Lcpidodcttdroii 

 and Bothrodctidrou are found to bear two opposite rows 

 of large depressed scars. Such stems are said to be in 

 the Ulodendroid condition, and were formerly included in 

 the " genus " Ulodctidroti. 



These curious Ulodendroid scars were known ver}' 

 early in the study of Pala;obotany, and many explana- 

 tions of their meaning and mode of formation have been 

 put forward. 



The explanation which has secured general accept- 

 ance is that they bore sessile cones which were not 

 attached to the whole area of the scar, but onh' to the 

 central or sub-central umbilicus, and which by their 

 pressure, obliterated the leaf bases over the whole area of 

 the scar. 



The large size of the scars is explained by the 

 supporters of this theory as due to growth subsequent to 

 formation, and to the shedding of the cones. 



Other views which have been put forward, but which 

 have not secured any wide acceptance, are : — 



I. That due to Stur, who supposed the scars to have 

 been produced by the pressure of the bases of bulbils. 



This view is a modification of the ordinary view, and 

 is explained b\- the fact that Stur knew that certain 



January yi/i, igoS. 



