208 



STUDIES IN FOSSIL BOTANY 



marked longitudinal seriation of ' the soars affords, in 

 typical cases, the most obvious distinction from the 

 sculpturing of Lepidodendron. The scars are not always 

 seated on distinct leaf-cushions, or if such cushions are 

 present, they are not much larger than the scars them- 

 selves (Fig. 86). The individual leaf-scar has, as a rule, 

 an approximately hexagonal outline, with the angles 

 more or less rounded (see Figs. 86-89). The form 



Fig. 87. — Sigillaria mamillaris (Rhytidolepis type). Surface of stem, showing vertical 

 ribs with leaf-scars"(/.j.) and scars of the cones (c.s.). Nat. size. After Zeiller. 



of the scar varies much, not only in different species, 

 but on different parts of the same stem ; as the stem 

 increased in diameter with age, the scars not only 

 became more widely separated, but were also them- 

 selves stretched out in the horizontal direction. 



The prints on the scar are essentially similar to those 

 of Lepidodendron, and are here also three in number, 

 forming a transverse row, usually a little above the 

 centre of the scar (see Fig. 88). The middle print, 



