98 TRANSACTIONS. NATURAL IIISTOUY SOCIETY OF GLASGOW. 



in diameter, and the leaf-scar measures a quarter of an inch 

 across (No. 2135).* 



In both Sigillaria discophora and Sigillaria Taylori the cone 

 scars are usually more or less distant, but in the former species I 

 have observed on some specimens the cone-scars little distant 

 from each other, or even touching (No. 423), when the plant 

 becomes the Sigillaria (J) (Ulodendron) sub-discophora, Weiss and 

 Sterzel, which, however, is merely a varietal form of Sigillaria 

 discojihora, Konig sp.^ 



The Ulodendroid Slgillarice and Lepidodendrve are frequent in 

 Scotland, and I have been able in Lepidodendroii Velthemianum, 

 Sternb., to trace the formation of the cup-like depressions from 

 its earliest condition to that of their occurrence on aged stems. 

 In the earliest state the young cone is placed on a slightly- 

 elevated blunt boss, on the whole of whose surface the leaf-scars 

 are still present, radiating in spirals from the point to which the 

 cone is attached, which point subsequently forms the umbilicus 

 of the scar.^ Gradually the bark grows up round the base of the 

 sessile cone, and thus a cup-like depression is formed, which con- 

 tinues to increase in size after the cone has been shed. During 

 the period of attachment of the cone the pressure exerted by its 

 base on the bark effaces the leaf-scars, whose existence is 

 eventually only indicated by the little " dot " of their vascular 

 bundle. 



Professor D'Arcy Thomson figured a specimen of Sigillaria 

 Taylori with a cone attached to the stem,^ under the name of 

 Ulodendron minus. Another example showing the cones attached 

 in a young condition, and now in my possession (No. 16), was 

 discovered by Dr. Macfarlane in the Midlothian Oil Shales. 

 This specimen I figured and described in 1885.^ 



The stem of Sigillaria seems very rarely to have been branched, 

 and certainly never to have produced the much-dichotomously 



1 From Nab Eud Fly, near Halifax, Yorkshire. Millstone Grit. 



- Die SigiUaricn dtr preuix. Sieiiik. v. Rothi. Gebifte. II. Die Gruppe 

 der 6ubsiiiillaritn, p. 58, PI. XXVIII., fig. 107. 1893. 



^Kidston, Ann. and Mag. Nat. Hist., Ser. 5, Vol. XVI., p. 163, PI. 

 IV., fig. 2. 1885. 



* Trans. Edin. Geol. Soc, Vol. III., Part iii. 1880. 



^ Kidston, Annals and Mug. Nat. Hist., I.e., PI. V., fig. 9. 



